On Tue, 2018-07-24 at 23:06 +0900, Tomasz Figa wrote: > Due to complexity of the video encoding process, the V4L2 drivers of > stateful encoder hardware require specific sequences of V4L2 API calls > to be followed. These include capability enumeration, initialization, > encoding, encode parameters change, drain and reset. > > 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 encoder part of > the Codec API. > > Signed-off-by: Tomasz Figa <tfiga@xxxxxxxxxxxx> Thanks a lot for the update, > --- > Documentation/media/uapi/v4l/dev-encoder.rst | 550 +++++++++++++++++++ > Documentation/media/uapi/v4l/devices.rst | 1 + > Documentation/media/uapi/v4l/v4l2.rst | 2 + > 3 files changed, 553 insertions(+) > create mode 100644 Documentation/media/uapi/v4l/dev-encoder.rst > > diff --git a/Documentation/media/uapi/v4l/dev-encoder.rst b/Documentation/media/uapi/v4l/dev-encoder.rst > new file mode 100644 > index 000000000000..28be1698e99c > --- /dev/null > +++ b/Documentation/media/uapi/v4l/dev-encoder.rst > @@ -0,0 +1,550 @@ > +.. -*- coding: utf-8; mode: rst -*- > + > +.. _encoder: > + > +**************************************** > +Memory-to-memory Video Encoder Interface > +**************************************** > + > +Input data to a video encoder are raw video frames in display order > +to be encoded into the output bitstream. Output data are complete chunks of > +valid bitstream, including all metadata, headers, etc. The resulting stream > +must not need any further post-processing by the client. > + > +Performing software stream processing, header generation etc. in the driver > +in order to support this interface is strongly discouraged. In case such > +operations are needed, use of Stateless Video Encoder Interface (in > +development) is strongly advised. > + [...] > + > +Commit points > +============= > + > +Setting formats and allocating buffers triggers changes in the behavior > +of the driver. > + > +1. Setting format on ``CAPTURE`` queue may change the set of formats > + supported/advertised on the ``OUTPUT`` queue. In particular, it also > + means that ``OUTPUT`` format may be reset and the client must not > + rely on the previously set format being preserved. Since the only property of the CAPTURE format that can be set directly via S_FMT is the pixelformat, should this be made explicit? 1. Setting pixelformat on ``CAPTURE`` queue may change the set of formats supported/advertised on the ``OUTPUT`` queue. In particular, it also means that ``OUTPUT`` format may be reset and the client must not rely on the previously set format being preserved. ? > +2. Enumerating formats on ``OUTPUT`` queue must only return formats > + supported for the ``CAPTURE`` format currently set. Same here, as it usually is the codec selected by CAPTURE pixelformat that determines the supported OUTPUT pixelformats and resolutions. 2. Enumerating formats on ``OUTPUT`` queue must only return formats supported for the ``CAPTURE`` pixelformat currently set. This could prevent the possible misconception that the CAPTURE width/height might in any form limit the OUTPUT format, when in fact it is determined by it. > +3. Setting/changing format on ``OUTPUT`` queue does not change formats > + available on ``CAPTURE`` queue. 3. Setting/changing format on the ``OUTPUT`` queue does not change pixelformats available on the ``CAPTURE`` queue. ? Because setting OUTPUT width/height or CROP SELECTION very much limits the possible values of CAPTURE width/height. Maybe 'available' in this context should be specified somewhere to mean 'returned by ENUM_FMT and allowed by S_FMT/TRY_FMT'. > + An attempt to set ``OUTPUT`` format that > + is not supported for the currently selected ``CAPTURE`` format must > + result in the driver adjusting the requested format to an acceptable > + one. An attempt to set ``OUTPUT`` format that is not supported for the currently selected ``CAPTURE`` pixelformat must result in the driver adjusting the requested format to an acceptable one. > +4. Enumerating formats on ``CAPTURE`` queue always returns the full set of > + supported coded formats, irrespective of the current ``OUTPUT`` > + format. > + > +5. After allocating buffers on the ``CAPTURE`` queue, it is not possible to > + change format on it. > + > +To summarize, setting formats and allocation must always start with the > +``CAPTURE`` queue and the ``CAPTURE`` queue is the master that governs the > +set of supported formats for the ``OUTPUT`` queue. To summarize, setting formats and allocation must always start with setting the encoded pixelformat on the ``CAPTURE`` queue. The ``CAPTURE`` queue is the master that governs the set of supported formats for the ``OUTPUT`` queue. Or is this too verbose? regards Philipp
