Le mardi 05 juillet 2022 à 13:34 +0100, Dave Stevenson a écrit : > Hi Ming and Nicolas > > On Mon, 4 Jul 2022 at 16:53, Nicolas Dufresne <nicolas@xxxxxxxxxxxx> wrote: > > > > Le mardi 28 juin 2022 à 10:19 +0800, Ming Qian a écrit : > > > By setting the V4L2_BUF_FLAG_CODECCONFIG flag, > > > user-space should be able to hint decoder > > > the vb2 only contains codec config header, > > > but does not contain any frame data. > > > It's only used for parsing header, and can't be decoded. > > > > This is copied from OMX specification. I think we we import this, we should at > > least refer to the original. > > > > > > > > Current, it's usually used by android. > > > > > > Signed-off-by: Ming Qian <ming.qian@xxxxxxx> > > > --- > > > Documentation/userspace-api/media/v4l/buffer.rst | 9 +++++++++ > > > include/uapi/linux/videodev2.h | 2 ++ > > > 2 files changed, 11 insertions(+) > > > > > > diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst > > > index 4638ec64db00..acdc4556f4f4 100644 > > > --- a/Documentation/userspace-api/media/v4l/buffer.rst > > > +++ b/Documentation/userspace-api/media/v4l/buffer.rst > > > @@ -607,6 +607,15 @@ Buffer Flags > > > the format. Any subsequent call to the > > > :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore, > > > but return an ``EPIPE`` error code. > > > + * .. _`V4L2-BUF-FLAG-CODECCONFIG`: > > > + > > > + - ``V4L2_BUF_FLAG_CODECCONFIG`` > > > + - 0x00200000 > > > + - This flag may be set when the buffer only contains codec config > > > + header, but does not contain any frame data. Usually the codec config > > > + header is merged to the next idr frame, with the flag > > > + ``V4L2_BUF_FLAG_KEYFRAME``, but there is still some scenes that will > > > + split the header and queue it separately. > > > > I think the documentation is clear. Now, if a driver uses this, will existing > > userland (perhaps good to check GStreamer, FFMPEG and Chromium ?) will break ? > > So we need existing driver to do this when flagged to, and just copy/append when > > the userland didn't opt-in that feature ? > > The commit text says it is for userspace feeding data into a video > decoder, so it's a userspace choice instead of driver. I see, the spec needs to be more clear then. > > For encoders there is already V4L2_CID_MPEG_VIDEO_HEADER_MODE [1] > which allows for V4L2_MPEG_VIDEO_HEADER_MODE_SEPARATE or > V4L2_MPEG_VIDEO_HEADER_MODE_JOINED_WITH_1ST_FRAME. FFmpeg selects > _SEPARATE by default [2], whilst the default is normally > _JOINED_WITH_1ST_FRAME. I did miss the addition of this API, thanks for the reminder. The problem right now is that things are being added with the needed cross-reference. > > It does raise the question as to whether all decoders will support > header byte only buffers, and does there need to be a capabilities > flag to denote that it is supported. > And should encoders in V4L2_MPEG_VIDEO_HEADER_MODE_SEPARATE mode set > it on the headers only buffers? What about: - Document better that in absence of V4L2_CID_MPEG_VIDEO_HEADER_MODE in a driver, V4L2_MPEG_VIDEO_HEADER_MODE_JOINED_WITH_1ST_FRAME is to be assumed - Document that in V4L2_MPEG_VIDEO_HEADER_MODE_SEPARATE, driver should signal the header buffer with the newly added buffer flag (I would suggest V4L2_BUF_FLAG_HEADERS_ONLY) - Document for each support CODECs if V4L2_CID_MPEG_VIDEO_HEADER_MODE can be supported, and the expected headers and the packing of these - Document that decoders that didn't implement V4L2_CID_MPEG_VIDEO_HEADER_MODE should be assumed to only support V4L2_MPEG_VIDEO_HEADER_MODE_JOINED_WITH_1ST_FRAME decoding (even though it allowed to support any alignment, even random). - Cross-reference V4L2_CID_MPEG_VIDEO_HEADER_MODE into the new flag documentation (whatever this new flag will be called). > > A number of undefined elements of how this should be implemented/used :-( > > Dave > > [1] https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-codec.html > [2] https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/v4l2_m2m_enc.c#L196 > > > > * .. _`V4L2-BUF-FLAG-REQUEST-FD`: > > > > > > - ``V4L2_BUF_FLAG_REQUEST_FD`` > > > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h > > > index 5311ac4fde35..8708ef257710 100644 > > > --- a/include/uapi/linux/videodev2.h > > > +++ b/include/uapi/linux/videodev2.h > > > @@ -1131,6 +1131,8 @@ static inline __u64 v4l2_timeval_to_ns(const struct timeval *tv) > > > #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE 0x00010000 > > > /* mem2mem encoder/decoder */ > > > #define V4L2_BUF_FLAG_LAST 0x00100000 > > > +/* Buffer only contains codec header */ > > > +#define V4L2_BUF_FLAG_CODECCONFIG 0x00200000 > > > /* request_fd is valid */ > > > #define V4L2_BUF_FLAG_REQUEST_FD 0x00800000 > > > > >
