media-workshop

media-workshop@linuxtv.org

113 discussions

Re: [media-workshop] [ANNOUNCE] media workshop in November
by Hans de Goede 19 Sep '12

19 Sep '12

Hi All, Mauro Carvalho Chehab wrote: > As there will be several developers speaking about the media subsystem at > both LinuxCon and ELCE, we decided to take just one day (September, 8th) > for the media workshop (while we expect that we'll likely have some other > discussions during the week). I will be attending parts of the day. November 8 overlaps with the KVM forum, and I'm giving a talk there, as well as likely be involved in various KVM discussions, etc. So count on me, but don't count on me too much :) Regards, Hans

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attending multimedia workshop
by Jean-Paul Saman 19 Sep '12

19 Sep '12

Since I am in Barcelona for the LinuxCon/ELC Europe event it is my intention to also attend the multimedia workshop on behalf of the VideoLAN project and of my own interests. Kind regards, Jean-Paul Saman.

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[Workshop-2011] [ANNOUNCE] workshop mailing list got renamed to media-workshop@linuxtv.org
by Mauro Carvalho Chehab 19 Sep '12

19 Sep '12

Dear developers, In order to avoid the need of creating a new mailing list for each new media Workshop, it seems a way better to just re-use the existing mailing list for it. We did it, actually for the KS/2012 Workshop. Yet, it looks weird to use a list called "Workshop-2011" for it ;) So, I've renamed this mailing list to "media-workshop(a)linuxtv.org". All the past emails are preserved at the archives, under: http://www.linuxtv.org/pipermail/media-workshop/ Regards, Mauro

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[Workshop-2011] Media summit at the Kernel Summit - was: Fwd: Re: [Ksummit-2012-discuss] Organising Mini Summits within the Kernel Summit
by Mauro Carvalho Chehab 13 Sep '12

13 Sep '12

As we did in 2012, we're planning to do a media summit again at KS/2012. The KS/2012 will happen in San Diego, CA, US, between Aug 26-28, just before the LinuxCon North America. In order to do it, I'd like to know who is interested on participate, and to get proposals about what subjects will be discussed there, in order to start planning the agenda. Thanks! Mauro -------- Mensagem original -------- Assunto: Re: [Ksummit-2012-discuss] Organising Mini Summits within the Kernel Summit Data: Fri, 13 Jul 2012 13:37:08 -0400 De: Theodore Ts'o <tytso(a)mit.edu> Para: James Bottomley <James.Bottomley(a)HansenPartnership.com> CC: ksummit-2012-discuss(a)lists.linux-foundation.org, linux-kernel <linux-kernel(a)vger.kernel.org> On Wed, Jul 11, 2012 at 09:09:15AM +0100, James Bottomley wrote: > Hi All, > > We have set aside the second day of the kernel summit (Tuesday 28 > August) as mini-summit day. So far we have only the PCI mini summit on > this day, so if you can think of other topics, please send them to the > kernel summit discuss list: > > ksummit-2012-discuss(a)lists.linux-foundation.org > > Looking at the available rooms, we think we can run about four or five > mini summits. > > As an added incentive, mini summit organisers get to pick who they > invite and all the people they pick will get an automatic invitation to > the third day of the kernel summit (but not the core first day) and the > evening events. OK, so far I believe I've heard concrete suggestions from identified (or fairly well identified :-) stuckees willing to organize mini-summits for: * ARM * Media * PCI * memcg I may have missed some, so if people could send a message to the discuss list with [MINI-SUMMIT] in the subbject line and the name of the proposed mini-summit, that would be really helpful. Please indicate whether you are volunteering to help organize the proposed mini-summit, or identify someone you think can be volunteered. :-) Things that we will be asking the mini-summit chars to determine, in addition to who should be given invites for Tuesday and Wednesday is an estimate of how much time you need, and a list of sub-topics (and who might lead the sub-topic discussion). We will be asking you to create a fairly well-defined schedule, with 30 and 60 minute slots, so that we can publish a schedule and so that people who might need to hop between mini-summits, have a chance to do so. So please start thinking about how long each of your sub-topics will need to be, and who might be needed for a particular sub-topic's discussion to be successful. There may be a number of developers, with fingers in multiple subsystem, where scheduling may become a bit of a challenge. Thanks!! - Ted _______________________________________________ Ksummit-2012-discuss mailing list Ksummit-2012-discuss(a)lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/ksummit-2012-discuss

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[Workshop-2011] Notes from the KS/2012 Media Workshop - part 1
by Mauro Carvalho Chehab 10 Sep '12

10 Sep '12

I finished reviewing the etherpad notes for the first two themes. Wwell, it was actually 3, so I decided to break in 3 at our notes: - V4L2 Ambiguities - V4L2 compliance - V4L2 and ALSA I should be sending it also to LWN for them to publish it and make visible for other Kernel developers that couldn't came. I probably won't have time to finish the review for the rest of the media workshop before next week, as I'm leaving San Diego today. So, feel free to help me with that ;) In particular, I feel that we discussed much more on the other topics than the notes might be showing. So, we need to take a look on every presentation and try to remember and document what decisions were taken there, likely enclosing the most important points from the slides into our final notes. I'd appreciate if someone could help on that, as I probably won't be able do do it before Wed. Regards, Mauro --- 1. V4L2 Ambiguities The first topic is with regards to V4L2 API ambiguities that need to be addressed, in order to avoid inconsistent behavior between drivers. 1.1. Split off controls Split off the control part from videodev2.h. Controls are almost 30% of videodev2.h (and growing). Maintaining controls would be easier if they are moved to e.g. linux/v4l2-controls.h which is included by videodev2.h Results: OK, split them from videodev2.h to v4l2-controls.h 1.2. Driver-specific controls Should driver-specific controls have a unique CID, or can the CIDs overlap ? Currently there are three types of controls: standard controls, controls that are specific to a chipset (e.g. cx2341x, mfc51) and driver-specific controls. The controls of the first two types have well defined and unique IDs. For driver-specific controls however there are no clear rules. It all depends on one question: should driver-specific controls have a unique control ID as well, or can they overlap with other drivers? If the answer is that they should be unique as well, then all driver-specific controls will have to be defined in a single header so you can be certain that there is no overlap. Results: New controls should not overlap. Having all driver-specific controls in a single header file would probably be overkill. We can instead reserve a range of CIDs for each driver, and define the range base CID only in a common header file. Driver-specific CIDs themselves would be defined in driver-specific headers. 1.3. STREAMON/STREAMOFF What should VIDIOC_STREAMON/OFF do if the stream is already started/stopped? I believe they should do nothing and just return 0. The main reason for that is it can be useful if an application can just call VIDIOC_STREAMOFF without having to check whether streaming is in progress. Results: STREAMON/STREAMOFF should return success (0) if the stream is already started/stopped, to avoid potentially breaking existing applications. 1.4. Unsupported formats in TRY_FMT/S_FMT What should a driver return in TRY_FMT/S_FMT if the requested format is not supported (possible behaviors include returning the currently selected format or a default format). The spec says this: "Drivers should not return an error code unless the input is ambiguous", but it does not explain what constitutes an ambiguous input. In my opinion TRY/S_FMT should never return an error other than EINVAL (if the buffer type is unsupported) or EBUSY (for S_FMT if streaming is in progress). Should we make a recommendation whether the currently selected format or a default format should be returned? One proposal is to just return a default format if the requested pixelformat is unsupported. Returning the currently selected format leads to inconsistent results. Results: TRY_FMT/S_FMT should never return an error when the requested format is not supported. Drivers should always return a valid format, preferably a format that is as widely supported by applications as possible. Both TRY_FMT and S_FMT should have the same behaviour. Drivers should not return different formats when getting the same input parameters. The format returned should be a driver default format if possible (stateless behaviour) but can be stateful if needed. The API spec should let clear that format retuns may be different when different video inputs (or outputs) are selected. 1.5. Empty VIDIOC_QUERYCAP bus_info VIDIOC_QUERYCAP allows bus_info to be empty. Since the purpose of bus_info is to distinguish multiple identical devices this makes no sense. I propose to make the spec more strict and require that bus_info is always filled in with a unique string. Results: bus_info should never be empty. The spec should specify the syntax of the field contents for common busses, like PCI e USB. 1.6. Deprecate V4L2_BUF_TYPE_PRIVATE None of the kernel drivers use it, and I cannot see any good use-case for this. If some new type of buffer is needed, then that should be added instead of allowing someone to abuse this buffer type. Results: Not used upstream, should be deprecated. 1.7. Buftype checks against node type A driver that has both a video node and a vbi node using the same struct v4l2_ioctl_ops for both nodes will have to check in e.g. vidioc_g_fmt_vid_cap or vidioc_g_fmt_vbi_cap whether it is called from the correct node (video or vbi) and return an error if it isn't. Should such checks be added to the V4L2 core? And if so, should we add some additional VFL types? Currently we have GRABBER (video nodes), VBI, RADIO and SUBDEV. But if we want to do proper core checks, then we would also need OUTPUT, VBI_OUT and M2M. We could also refuse ioctls based on the VFL_TYPE: e.g. VIDIOC_ENCODER_CMD makes no sense for radio/vbi nodes. Easy to implement with the lookup table. Results: It should first be needed to check whether this could break applications, before enforcing it at the core. 1.8. Remove experimental tag from old drivers Remove the experimental tag from the following old drivers: VIDEO_TLV320AIC23B USB_STKWEBCAM VIDEO_CX18 VIDEO_CX18_ALSA VIDEO_ZORAN_AVS6EYES DVB_USB_AF9005 MEDIA_TUNER_TEA5761 Removing this tag from these drivers might be too soon, though: VIDEO_NOON010PC30 VIDEO_OMAP3 Results: Remove the tag from the first set of old drivers. It is too soon for VIDEO_OMAP3. With regards to VIDEO_NOON010PC30, it was marked as experimental only because it used VIDEO_V4L2_SUBDEV_API, which in turn depends on EXPERIMENTAL. Otherwise it's pretty standard and simple sensor driver. Hence the experimental tag could probably just be removed. 1.9. Remove ioctl's experimental tag Remove the experimental tag from the V4L2 API elements: Video Output Overlay (OSD) Interface (from the section “Video Output Overlay Interface”). V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY. V4L2_CAP_VIDEO_OUTPUT_OVERLAY. VIDIOC_ENUM_FRAMESIZES and VIDIOC_ENUM_FRAMEINTERVALS ioctls. VIDIOC_G_ENC_INDEX ioctl. VIDIOC_ENCODER_CMD and VIDIOC_TRY_ENCODER_CMD ioctls. VIDIOC_DECODER_CMD and VIDIOC_TRY_DECODER_CMD ioctls. Results: Remove experimental tag from listed ioctls. 1.10. Wrong timings API use for input What should VIDIOC_G_STD/DV_PRESET/DV_TIMINGS return if the current input or output does not support that particular timing approach? EINVAL? ENODATA? This is relevant for the case where a driver has multiple inputs/outputs where some are SDTV (and support the STD API) and others are HDTV (and support the DV_TIMINGS API). I propose ENODATA. Results: EINVAL is not a good error code, ENODATA is a better possibility. Let's stick with the latest one. 1.11. New defines for DV timing API Add these new defines: #define V4L2_IN_CAP_TIMINGS V4L2_IN_CAP_CUSTOM_TIMINGS #define V4L2_OUT_CAP_TIMINGS V4L2_OUT_CAP_CUSTOM_TIMINGS Since DV_TIMINGS is now used for any HDTV timings and no longer just for custom, non-standard timings, the word "CUSTOM" is no longer appropriate. Results: Rename them to V4L2_IN_CAP_TIMINGS and V4L2_OUT_CAP_TIMINGS Turn V4L2_(IN|OUT)_CAP_CUSTOM_TIMINGS into aliases for V4L2_(IN|OUT)_CAP_TIMINGS Deprecate V4L2_(IN|OUT)_CAP_CUSTOM_TIMINGS. 1.12. Sequence and timestamp for output What should video output drivers do with the sequence and timestamp fields when they return a v4l2_buffer from VIDIOC_DQBUF? I think the spec is clear with respect to the timestamp: "The driver stores the time at which the first data byte was actually sent out in the timestamp field." For sequence the spec just says: "Set by the driver, counting the frames in the sequence." So I think that output drivers should indeed set both sequence and timestamp. Results: For capture and output, the behaviour is OK, the documentation should be clarified. For mem2mem, we need to specify the behaviour. Timestamp are not actually needed, but it is needed a way to match buffers on both sides, as the codec can reorder them, and timestamps, together with sequence numbers are used for it. An RFC should be sent to the list. 1.13. Const arg for write-only ioctls Make the argument of write-only ioctls const in v4l2-ioctls.h. This makes it obvious to drivers that they shouldn't change the contents of the input struct since it won't make it back to userspace. It also simplifies v4l2-ioctl.c since it can rely on the fact that after the ioctl call the contents of the struct hasn't changed. Right now the struct contents is logged (if debugging is on) before the ioctl call for write-only ioctls. Results: Yes. 1.14. How to set the timestamp? What is the right/best way to set the timestamp? The spec says gettimeofday, but is it my understanding that ktime_get_ts is much more efficient. Some drivers are already using ktime_get_ts. Options: all drivers must comply to the spec and use gettimeofday we change the spec and all drivers must use the more efficient ktime_get_ts we add a buffer flag V4L2_BUF_FLAG_MONOTONIC to tell userspace that a monotonic clock like ktime_get_ts is used and all drivers that use ktime_get_ts should set that flag. If we go for c, then we should add a recommendation to use one or the other as the preferred timestamp for new drivers. Results: ktime_get_ts() should be used. Change the spec, and require all drivers to be fixed. A new driver capability flag is needed to tell applications that the driver uses the monotonic clock. 1.15. Device specified clock Some devices provide their own timestamp in device clock units. How should that be passed on to userspace? Proposal: extend the struct v4l2_timecode in v4l2_buffer, either by just adding a new type, or by creating an anonymous union. Currently there are no drivers that use v4l2_timecode. It is questionable for v4l2_timecode to be in v4l2_buffer at all since such information will typically be carried over VBI. Results: Reuse v4l2_timecode to pass the device clock timestamp to userspace (making it an anonymous union is an option, as it would allow different kind of timestamps later) and add a capability flag to inform applications. 1.16. V4L2_CAP_VIDEO_CAPTURE If a driver supports only formats with more than one plane, should V4L2_CAP_VIDEO_CAPTURE still be defined? And if a driver also supports single-plane formats in addition to >1 plane formats, should V4L2_CAP_VIDEO_CAPTURE be compulsary? The consensus seems to be 'No' and 'No'. The CAPs refer to whether the single and/or multiplanar API is implemented, not whether single and/or multiplanar formats are available. Results: Flags should reflect what it is visible/usable by the userspace API; reviewing v4l-utils with that regards may be needed, due to emulation code that could be there. 1.17. V4L2_CROPCAP VIDIOC_CROPCAP: the spec says that CROPCAP must be implemented by all capture and output devices (Section "Image Cropping, Inserting and Scaling"). In reality only a subset of the drivers support cropcap. Should cropcap really be compulsory? Or only for drivers that can scale? And in that case, should we make a default implementation for those drivers that do not support it? (E.g.: call g_fmt and use the width/height as the default and bounds rectangles, and set the pixel aspect to 1/1) Results: the ioctls should not be mandatory if the driver doesn't support crop or scale. 1.18. Pixel aspect ratio Pixel aspect: currently this is only available through VIDIOC_CROPCAP. It never really belonged to VIDIOC_CROPCAP IMHO. It's just not a property of cropping/composing. It really belongs to the input/output timings (STD or DV_TIMINGS). That's where the pixel aspect ratio is determined. While it is possible to add it to the dv_timings struct, I see no way of cleanly adding it to struct v4l2_standard (mostly because VIDIOC_ENUMSTD is now handled inside the V4L2 core and doesn't call the drivers anymore). An alternative is to add it to struct v4l2_input/output, but I don't know if it is possible to defined a pixelaspect for inputs that are not the current input. What I am thinking of is just to add a new ioctl for this VIDIOC_G_PIXELASPECT. Results: TBD on the mailing list. 1.19. Tuner ownership How to handle tuner ownership if both a video and radio node share the same tuner? Obvious rules: Calling S_FREQ, S_TUNER, S_MODULATOR or S_HW_FREQ_SEEK will make the filehandle the owner if possible. EBUSY is returned if someone else owns the tuner and you would need to switch the tuner mode. Ditto for ioctls that expect a valid tuner configuration like QUERYSTD. This is likely to be driver dependent, though. Just opening a device node should not switch ownership But it is not clear what to do when any of these ioctls are called: G_FREQUENCY: could just return the last set frequency for radio or TV: requires that that is remembered when switching ownership. This is what happens today, so G_FREQUENCY does not have to switch ownership. G_TUNER: the rxsubchans, signal and afc fields all require ownership of the tuner. So in principle you would want to switch ownership when G_TUNER is called. On the other hand, that would mean that calling v4l2-ctl --all -d /dev/radio0 would change tuner ownership to radio for /dev/video0. That's rather unexpected.It is possible to just set rxsubchans, signal and afc to 0 if the device node doesn't own the tuner. I'm inclined to do that. Should closing a device node switch ownership? E.g. if nobody has a radio device open, should the tuner switch back to TV mode automatically? I don't think it should. How about hybrid tuners? Results: TBD on the mailing list (or later this week). 2. V4L2 Compliance An automated tool to test whether a driver complies with the spec was written, in order to allow being sure that drivers will match the V4L2 spec. Known missing tests at V4L2 compliance: Cropping: VIDIOC_CROPCAP, VIDIOC_G/S_CROP, VIDIOC_G/S_SELECTION Framebuffer: VIDIOC_S_FBUF, OVERLAY Encoder/Decoder: VIDIOC_(TRY_)ENCODER_CMD, VIDIOC_(TRY_)DECODER_CMD, VIDIOC_G_ENC_INDEX Streaming: VIDIOC_QBUF, DQBUF, QUERYBUF, PREPARE_BUFS, VIDIOC_STREAMON/OFF Subdev API, MC API (but these are possibly out-of-scope anyway) Extra tests – It requires: G/S_PRIORITY Normal and extended controls Control events videobuf2 (or an own video buffers implementation that is spec-compliant, videobuf1 isn"t) Results: Passing v4l2-compliance tests will be compulsory for new drivers under drivers/media. The enforcement of the extra tests are ok. However, the usage of videobuf2 can't be mandatory yet for all drivers, as VB2 currently lacks support for videobuf-dvb. So, hybrid drivers may use VB1 instead, while this is not fixed on VB2. Lots of work is required to make existing drivers compliant; as almost all fails, but merging newer drivers without passing with the tests would mean further re-work, with should really be avoided. In order for it to work, it would also require that new tests should be added whenever a new API appears. The V4L2 streaming profile needs to be implemented to support complex MC drivers in v4l2-compliance. 3. ALSA+V4L2 There are some pending issues related to the needs at ALSA by V4L2 drivers. 3.1. Compressed audio (ivtv, pvrusb2) Currently, two audio drivers (ivtv and pvrusb2) currently provides pure audio mpeg TS streams, either at video or radio node, in order for the cards to work with FM radio. This is an API violation that should be fixed. Also, newer radio USB sticks might also have compressed radio support. So, it is needed a way to move the existing devices and enforce newer ones to use ALSA api for audio-only output. During the discussions, Takashi Iwai (ALSA maintainer) said that the compressed audio format support for ALSA, including sound drivers, will be supported in 3.7. Patches to add support in driver were added on Aug, 20: http://git.kernel.org/?p=linux/kernel/git/broonie/sound.git;a=commit;h=c514… Yet, the userspace ALSA library currently doesn't support yet, as it currently on a separate library. tinycompress: http://git.alsa-project.org/?p=tinycompress.git;a=summary Vinod Koul (vinod.koul(a)linux.intel.com) is working with the userspace library. It seems that there's no technical reason why not adding it at alsalib, so it was proposed that this should be merged at alsalib, in order to allow the drivers conversions. The headers for the kernel API are inside the git://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git tree, at: include/sounds/compress_params.h include/sounds/compress_offload.h 3.2. timestamps Userspace needs to sync audio and video. V4L2 has timestamps already. Currently, alsalib provides the PCM_STATUS: current position, system time. There is no device timestamp at kernelspace, however; the time shift is calculated by knowing the sampling time. In opposite to pure audio devices, on audio and video devices, when capture starts, the audio can start later than video, or together with it, depending on the driver. Such time difference between audio and video could be calculated in order to adjust the initial drift, to be used as the initial timestamp for the start of the audio. However, audio/video delay may not remain constant. For example, when changing inputs, the audio can cut off while the input change is in progress, so there need to be a way to resync the audio timestamp. Also, small time drifts may happen during audio/video stream lifetime. So, it should be possible to have a way for the driver to periodically tag the audio stream with the time reference. In the case of compressed audio, the API has a timestamp already. So, no changes there should be needed. 3.3. Usage of media API by ALSA There's a requirement of using the media API also by ALSA, as this is needed on some embedded devices. As there will be some discussions about that theme at LPC, on Wednesday 11:40, at Nautilus 2 room: http://summit.linuxplumbersconf.org/lpc-2012/meeting/80/lpc2012-audio-routi… It was decided to not talk about that on this time slot. There is a preliminary ALSA RFC patches with such proposal at: http://comments.gmane.org/gmane.linux.alsa.devel/100537

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[Workshop-2011] Etherpad + links
by Hans Verkuil 31 Aug '12

31 Aug '12

Hi all, Here are the links to my presentations and below that the raw text of the etherpad. A more polished version will be posted to the mailinglist eventually, but that's probably going to be Monday at the earliest. Unless someone else wants to do this? My presentations: http://hverkuil.home.xs4all.nl/presentations/v4l2-workshop-2012.odp http://hverkuil.home.xs4all.nl/presentations/v4l2-compliance-workshop-2012.… http://hverkuil.home.xs4all.nl/presentations/v4l2-workshop-cec.odp The etherpad text: V4L2 Ambiguities * Split off controls OK, split them from videodev2.h to v4l2-controls.h * Driver-specific controls Should driver-specific controls have a unique CID, or can the CIDs overlap ? Having all driver-specific controls in a single header file would probably be overkill. We can instead reserve a range of CIDs for each driver, and define the range base CID only in a common header file. Driver-specific CIDs themselves would be defined in driver-specific headers. * STREAMON/STREAMOFF STREAMON/STREAMOFF should return success (0) if the stream is already started/stopped. * Unsupported formats in TRY_FMT/S_FMT TRY_FMT/S_FMT should never return an error when the requested format is not supported. Drivers should always return a valid format, preferably a format that is as widely supported by applications as possible. TRY_FMT and S_FMT should have the same behaviour. Drivers should not return different formats when getting the same input parameters. The format returned should be a driver default format if possible (stateless behaviour) but can be stateful if needed. * bus_info bus_info should never be empty. The spec should specify the syntax of the field contents for common busses. * V4L2_BUF_TYPE_PRIVATE Not used, should be deprecated. * Buftype checks against node type The V4L2 core should check that ioctls it receives match the device node type they're received on. This is currently not done if a driver supports for instance both video and vbi on two different nodes. The core accepts both ioctls on both nodes, and several drivers don't perform the check themselves. We first need to check whether this could break applications. * Remove experimental tag Remove the MEDIA_TUNER_TEA5761 driver. Too soon for VIDEO_OMAP3, to be decided for VIDEO_NOON010PC30 (ask Sylwester). Remove the experimental tag from other listed drivers. With regards to VIDEO_NOON010PC30, it was marked as experimental only because it used VIDEO_V4L2_SUBDEV_API, which in turn depends on EXPERIMENTAL. Otherwise it's pretty standard and simple sensor driver. Hence the experimental tag could probably just be removed. Remove experimental tag from listed ioctls. * Wrong timings API use for input Return an error. EINVAL is not a good error code, ENODATA is a better possibility. * New defines for DV timing API Add defines for V4L2_IN_CAP_TIMINGS and V4L2_OUT_CAP_TIMINGS, turn V4L2_(IN| OUT)_CAP_CUSTOM_TIMINGS into aliases for V4L2_(IN|OUT)_CAP_TIMINGS and deprecate V4L2_(IN|OUT)_CAP_CUSTOM_TIMINGS. * Sequence and timestamp for output For capture and output, the behaviour is OK, the documentation should be clarified. For mem2mem, we need to specify the behaviour. Timestamp are not needed, but we need a way to match buffers on both sides, as the codec can reorder them. An RFC should be sent to the list. * Const arg for write-only ioctls Yes. * How to set the timestamp ? We should use ktime_get_ts. Change the spec, and require all drivers to be fixed. A new driver capability flag is needed to tell applications that the driver uses the monotonic clock. * Device specified clock Reuse v4l2_timecode to pass the device clock timestamp to userspace (making it an anonymous union is an option, as it would allow different kind of timestamps later) and add a capability flag to inform applications. * V4L2_CAP_VIDEO_CAPTURE No and no. * V4L2_CROPCAP The ioctls should not be mandatory if the driver doesn't support crop or scale. * Pixel aspect ratio TBD on the mailing list. * Tuner ownership TBD on the mailing list (or later this week). V4L2 Compliance Automated tool to test whether a driver complies with the spec. Requirements: * G/S_PRIORITY * Normal and extended controls * Control events * videobuf2 (or an own video buffers implementation that is spec-compliant, videobuf1 isn"t) Passing v4l2-compliance tests will be compulsory for new drivers. Require that new tests are added wheenver a new API appears. The V4L2 streaming profile needs to be implemented to support complex MC drivers in v4l2-compliance. ALSA+V4L2 a) Compressed audio (ivtv, pvrusb2) Compressed audio format support for ALSA will be supported in 3.7. Patch to add support in driver: http://git.kernel.org/?p=linux/kernel/git/broonie/sound.git;a=commit;h=c514… But no userspace ALSA library support yet. It is currently on a separate library. tinycompress: http://git.alsa-project.org/?p=tinycompress.git;a=summary Vinod Koul - vinod.koul(a)linux.intel.com - is working with the userspace library Kernelspace: git.kernel.org, at linux/kernel/git/broonie/sound.git Header for kernel API include/sounds/compress_params.h include/sounds/compress_offload.h b) timestamps Userspace needs to sync audio and video. V4L2 has timestamps already. PCM_STATUS: current position, system time. There is no device timestamp. When capture starts the audio can start later than video. We can calculate this delay. Perhaps we can use this to set the initial timestamp of the start of the audio. But when changing inputs the audio can cut off while the input change is in progress, so there need to be a way to resync the audio timestamp. The compressed audio API has a timestamp already. c) usage of media API by ALSA There will be some discussions about that theme at LPC, on Wednesday 11:40, at Nautilus 2 room: http://summit.linuxplumbersconf.org/lpc-2012/meeting/80/lpc2012-audio-routi… Preliminary ALSA RFC patches: http://comments.gmane.org/gmane.linux.alsa.devel/100537 SoC Vendor Feedback TI: trying to get in touch with omap4/5 devs to see if we can help out. A poor design makes V4L2 impossible at the moment. Laurent will try to contact a few buffer. Question about zero-copy pipelining. Can be done with dmabuf. See this patch series: http://www.mail-archive.com/linux-media@vger.kernel.org/msg50525.html dmabuf documentation in the kernel: Documentation/dma-buf-sharing.txt Script to generate a large patch to update drivers/media from an older kernel to the latest code: http://git.linuxtv.org/hverkuil/cisco_build.git/blob_plain/cobalt- mainline:/patch-kernel.sh ST-Ericsson: Media Controller API: should be unified for V4L2 and ALSA. Did work on Media Controller connector entities. V4L2/DVB issues from userspace perspective Versioning: recommended method is to just copy videodev2.h. libv4l: needs to be released more often: distros will not upgrade unless a new release is made. The current is very old. Controls: which are relevant for userspace and which aren't? Profile driven? libv4l2: doesn't support userptr. Raise questions about this with the linux-media mailinglist and with a CC to Hans de Goede. CEC We need a new CEC bus (similar to I2C) with an in-kernel API and a userspace API exposed by the core (device or socket API ?) MC Library Media Device Discovery Library: work-in-progress. Enumerates media devices, then v4l2 etc.nodes. Uses libudev or sysfs as fallback. Android V4L2 Cam Library HAL library on top of V4L2. Preview, still images, capture works. Regards, Hans

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[Workshop-2011] Android V4L2 Library
by Mauro Carvalho Chehab 29 Aug '12

29 Aug '12

As we didn't have time yesterday for the Android library topic, we're planning to do it today, at the KS empty lot at 14:10, at Nautilus 3 room: http://summit.linuxplumbersconf.org/lpc-2012/meeting/161/ks2012-open-day-af… I'll be confirm it soon to the ML. Regards, Mauro

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[Workshop-2011] Agenda for the KS media workshop
by Mauro Carvalho Chehab 28 Aug '12

28 Aug '12

With regards to the KS media workshop, I did a few adjustments at the time scheduled for each activity, in order to match the break and lunch time used by the LPC conference. So, our agenda is: Agenda 9:00 - V4L2 API ambiguities + v4l2 compliance tool 10:00 - Media Controller library 10:35 - Break 10:45 - ALSA and V4L/Media Controller 11:35 - ARM and needed features for V4L/DVB 12:25 – Lunch 13:20 - SoC Vendors feedback – how to help them to go upstream 14:15 - V4L2/DVB issues from userspace perspective 15:10 - Android's V4L2 cam library 15:45 – Break 16:00 - HDMI CEC 16:45 - Synchronization, shared resource and optimizations 17:30 Of course, we can re-schedule some things, if are there conflicts with other workshops that would prevent the major contributors for a topic to be there (in particular, we hope to have enough people from other areas at ARM and ALSA topics). See you tomorrow! Mauro

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[Workshop-2011] V4L2 API ambiguities: workshop presentation
by Hans Verkuil 22 Aug '12

22 Aug '12

Hi all, I've prepared a presentation for the upcoming workshop based on my RFC and the comments I received. It is available here: http://hverkuil.home.xs4all.nl/presentations/v4l2-workshop-2012.odp http://hverkuil.home.xs4all.nl/presentations/v4l2-workshop-2012.pdf Attendees of the workshop: please review this before the workshop starts. I want to go through this list fairly quickly (particularly slides 1-14) so we can have more time for other topics. Regards, Hans

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[Workshop-2011] RFC: V4L2 API ambiguities
by Hans Verkuil 14 Aug '12

14 Aug '12

Hi all! As part of the 2012 Kernel Summit V4L2 workshop I will be discussing a bunch of V4L2 ambiguities/improvements. I've made a list of all the V4L2 issues and put them in two categories: issues that I think are easy to resolve (within a few minutes at most), and those that are harder. If you think I put something in the easy category that you believe is actually hard, then please let me know. If you attend the workshop, then please read through this and think about it a bit, particularly for the second category. If something is unclear, or you think another topic should be added, then let me know as well. Regards, Hans Easy: 1) Split off the control part from videodev2.h. Controls are almost 30% of videodev2.h. I think maintaining controls would be easier if they are moved to e.g. linux/v4l2-controls.h which is included by videodev2.h. 2) Currently there are three types of controls: standard controls, controls that are specific to a chipset (e.g. cx2341x, mfc51) and driver-specific controls. The controls of the first two types have well defined and unique IDs. For driver-specific controls however there are no clear rules. It all depends on one question: should driver-specific controls have a unique control ID as well, or can they overlap with other drivers? If the answer is that they should be unique as well, then all driver-specific controls will have to be defined in a single header so you can be certain that there is no overlap. If the answer is that they may overlap, then each driver can either define their controls inside their own driver, or in a driver-specific public header. In both cases a control ID range has to be defined for such controls, to ensure that they never clash with standard or chipset-specific control IDs. E.g. >= V4L2_CTRL_CLASS_XXX + 0x8000 (no overlap) or + 0xf000 (overlap allowed). My preference is to allow overlap. 3) What should VIDIOC_STREAMON/OFF do if the stream is already started/stopped? I believe they should do nothing and just return 0. The main reason for that is it can be useful if an application can just call VIDIOC_STREAMOFF without having to check whether streaming is in progress. 4) What should a driver return in TRY_FMT/S_FMT if the requested format is not supported (possible behaviours include returning the currently selected format or a default format). The spec says this: "Drivers should not return an error code unless the input is ambiguous", but it does not explain what constitutes an ambiguous input. Frankly, I can't think of any and in my opinion TRY/S_FMT should never return an error other than EINVAL (if the buffer type is unsupported) or EBUSY (for S_FMT if streaming is in progress). Returning an error for any other reason doesn't help the application since the app will have no way of knowing what to do next. 5) VIDIOC_QUERYCAP allows bus_info to be empty. Since the purpose of bus_info is to distinguish multiple identical devices this makes no sense. I propose to make the spec more strict and require that bus_info is always filled in with a unique string. 6) Deprecate V4L2_BUF_TYPE_PRIVATE. None of the kernel drivers use it, and I cannot see any good use-case for this. If some new type of buffer is needed, then that should be added instead of allowing someone to abuse this buffer type. 7) A driver that has both a video node and a vbi node (for example) that uses the same struct v4l2_ioctl_ops for both nodes will have to check in e.g. vidioc_g_fmt_vid_cap or vidioc_g_fmt_vbi_cap whether it is called from the correct node (video or vbi) and return an error if it isn't. That's an annoying test that can be done in the V4L2 core as well. Especially since few drivers actually test for that. Should such checks be added to the V4L2 core? And if so, should we add some additional VFL types? Currently we have GRABBER (video nodes), VBI, RADIO and SUBDEV. But if we want to do proper core checks, then we would also need OUTPUT, VBI_OUT and M2M. 8) Remove the experimental tag from the following old drivers: VIDEO_TLV320AIC23B USB_STKWEBCAM VIDEO_CX18 VIDEO_CX18_ALSA VIDEO_ZORAN_AVS6EYES DVB_USB_AF9005 MEDIA_TUNER_TEA5761 Removing this tag from these drivers might be too soon, though: VIDEO_NOON010PC30 VIDEO_OMAP3 9) What should VIDIOC_G_STD/DV_PRESET/DV_TIMINGS return if the current input or output does not support that particular timing approach? EINVAL? ENODATA? This is relevant for the case where a driver has multiple inputs/outputs where some are SDTV (and support the STD API) and others are HDTV (and support the DV_TIMINGS API). I propose ENODATA. 10) Proposal: add these defines: #define V4L2_IN_CAP_TIMINGS V4L2_IN_CAP_CUSTOM_TIMINGS #define V4L2_OUT_CAP_TIMINGS V4L2_OUT_CAP_CUSTOM_TIMINGS Since DV_TIMINGS is now used for any HDTV timings and no longer just for custom, non-standard timings, the word "CUSTOM" is no longer appropriate. 11) What should video output drivers do with the sequence and timestamp fields when they return a v4l2_buffer from VIDIOC_DQBUF? I think the spec is clear with respect to the timestamp: "The driver stores the time at which the first data byte was actually sent out in the timestamp field." For sequence the spec just says: "Set by the driver, counting the frames in the sequence." So I think that output drivers should indeed set both sequence and timestemp. 12) Make the argument of write-only ioctls const in v4l2-ioctls.h. This makes it obvious to drivers that they shouldn't change the contents of the input struct since it won't make it back to userspace. It also simplifies v4l2-ioctl.c since it can rely on the fact that after the ioctl call the contents of the struct hasn't changed. Right now the struct contents is logged (if debugging is on) before the ioctl call for write-only ioctls. Hard(er): 1) What is the right/best way to set the timestamp? The spec says gettimeofday, but is it my understanding that ktime_get_ts is much more efficient. Some drivers are already using ktime_get_ts. Options: a) all drivers must comply to the spec and use gettimeofday b) we change the spec and all drivers must use the more efficient ktime_get_ts c) we add a buffer flag V4L2_BUF_FLAG_MONOTONIC to tell userspace that a monotonic clock like ktime_get_ts is used and all drivers that use ktime_get_ts should set that flag. If we go for c, then we should add a recommendation to use one or the other as the preferred timestamp for new drivers. 2) If a driver supports only formats with more than one plane, should V4L2_CAP_VIDEO_CAPTURE still be defined? And if a driver also supports single-plane formats in addition to >1 plane formats, should V4L2_CAP_VIDEO_CAPTURE be compulsary? 3) VIDIOC_CROPCAP: the spec says that CROPCAP must be implemented by all capture and output devices (Section "Image Cropping, Inserting and Scaling"). In reality only a subset of the drivers support cropcap. Should cropcap really be compulsory? Or only for drivers that can scale? And in that case, should we make a default implementation for those drivers that do not support it? (E.g.: call g_fmt and use the width/height as the default and bounds rectangles, and set the pixel aspect to 1/1) 4) Pixel aspect: currently this is only available through VIDIOC_CROPCAP. It never really belonged to VIDIOC_CROPCAP IMHO. It's just not a property of cropping/composing. It really belongs to the input/output timings (STD or DV_TIMINGS). That's where the pixel aspect ratio is determined. While it is possible to add it to the dv_timings struct, I see no way of cleanly adding it to struct v4l2_standard (mostly because VIDIOC_ENUMSTD is now handled inside the V4L2 core and doesn't call the drivers anymore). An alternative is to add it to struct v4l2_input/output, but I don't know if it is possible to defined a pixelaspect for inputs that are not the current input. What I am thinking of is just to add a new ioctl for this VIDIOC_G_PIXELASPECT. The argument is then: struct v4l2_pixelaspect { __u32 type; struct v4l2_fract pixelaspect; __u32 reserved[5]; }; This combines well with the selection API. 5) How to handle tuner ownership if both a video and radio node share the same tuner? Obvious rules: - Calling S_FREQ, S_TUNER, S_MODULATOR or S_HW_FREQ_SEEK will change owner or return EBUSY if streaming is in progress. - Ditto for STREAMON, read/write and polling for read/write. - Ditto for ioctls that expect a valid tuner configuration like QUERYSTD. - Just opening a device node should *not* switch ownership. But it is not clear what to do when any of these ioctls are called: - G_FREQUENCY: could just return the last set frequency for radio or TV: requires that that is remembered when switching ownership. This is what happens today, so G_FREQUENCY does not have to switch ownership. - G_TUNER: the rxsubchans, signal and afc fields all require ownership of the tuner. So in principle you would want to switch ownership when G_TUNER is called. On the other hand, that would mean that calling v4l2-ctl --all -d /dev/radio0 would change tuner ownership to radio for /dev/video0. That's rather unexpected. It is possible to just set rxsubchans, signal and afc to 0 if the device node doesn't own the tuner. I'm inclined to do that. - Should closing a device node switch ownership? E.g. if nobody has a radio device open, should the tuner switch back to TV mode automatically? I don't think it should. - How about hybrid tuners?

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