On 1/24/19 11:04 AM, Tomasz Figa wrote: > Due to complexity of the video decoding process, the V4L2 drivers of > stateful decoder hardware require specific sequences of V4L2 API calls > to be followed. These include capability enumeration, initialization, > decoding, seek, pause, dynamic resolution change, drain and end of > stream. > > Specifics of the above have been discussed during Media Workshops at > LinuxCon Europe 2012 in Barcelona and then later Embedded Linux > Conference Europe 2014 in Düsseldorf. The de facto Codec API that > originated at those events was later implemented by the drivers we already > have merged in mainline, such as s5p-mfc or coda. > > The only thing missing was the real specification included as a part of > Linux Media documentation. Fix it now and document the decoder part of > the Codec API. > > Signed-off-by: Tomasz Figa <tfiga@xxxxxxxxxxxx> > --- > Documentation/media/uapi/v4l/dev-decoder.rst | 1076 +++++++++++++++++ > Documentation/media/uapi/v4l/dev-mem2mem.rst | 5 + > Documentation/media/uapi/v4l/pixfmt-v4l2.rst | 5 + > Documentation/media/uapi/v4l/v4l2.rst | 10 +- > .../media/uapi/v4l/vidioc-decoder-cmd.rst | 40 +- > Documentation/media/uapi/v4l/vidioc-g-fmt.rst | 14 + > 6 files changed, 1135 insertions(+), 15 deletions(-) > create mode 100644 Documentation/media/uapi/v4l/dev-decoder.rst > <snip> > +4. **This step only applies to coded formats that contain resolution information > + in the stream.** Continue queuing/dequeuing bitstream buffers to/from the > + ``OUTPUT`` queue via :c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQBUF`. The > + buffers will be processed and returned to the client in order, until > + required metadata to configure the ``CAPTURE`` queue are found. This is > + indicated by the decoder sending a ``V4L2_EVENT_SOURCE_CHANGE`` event with > + ``V4L2_EVENT_SRC_CH_RESOLUTION`` source change type. > + > + * It is not an error if the first buffer does not contain enough data for > + this to occur. Processing of the buffers will continue as long as more > + data is needed. > + > + * If data in a buffer that triggers the event is required to decode the > + first frame, it will not be returned to the client, until the > + initialization sequence completes and the frame is decoded. > + > + * If the client sets width and height of the ``OUTPUT`` format to 0, > + calling :c:func:`VIDIOC_G_FMT`, :c:func:`VIDIOC_S_FMT`, > + :c:func:`VIDIOC_TRY_FMT` or :c:func:`VIDIOC_REQBUFS` on the ``CAPTURE`` > + queue will return the ``-EACCES`` error code, until the decoder > + configures ``CAPTURE`` format according to stream metadata. I think this should also include the G/S_SELECTION ioctls, right? Regards, Hans
