On Tue, Dec 10, 2019 at 10:16 PM Dmitry Sepp <dmitry.sepp@xxxxxxxxxxxxxxx> wrote: > > Hi, > > Just to start, let's consider this v4l2 control: > V4L2_CID_MPEG_VIDEO_FRAME_RC_ENABLE. > As I can see, this control is referenced as a mandatory one in the Chromium > sources [1]. > > So could someone from the Chromium team please explain why it is mandatory? > (YouTube?) In fact, almost no encoders implement this control. Do we need it > in virtio-video? That control is used to encode videos in constant bitrate (CBR) mode, which is critical for real-time use case like video conferencing. However, that Chromium source code just requires *host-side* drivers to have the v4l2 control. Also, I guess it's rare that a guest app wants to use CQP instead of CBR from our experience. So, I suppose we can omit this control in virtio spec for now by assuming that guests always use CBR mode. Best regards, Keiichi > > [1] https://chromium.googlesource.com/chromium/src/media/+/refs/heads/master/ > gpu/v4l2/v4l2_video_encode_accelerator.cc#1500 > > Regards, > Dmitry. > > On Montag, 9. Dezember 2019 22:12:28 CET Enrico Granata wrote: > > +Changyeon Jo <changyeon@xxxxxxxxxx> for his awareness > > > > Thanks, > > - Enrico > > > > > > On Mon, Dec 9, 2019 at 6:20 AM Dmitry Sepp <dmitry.sepp@xxxxxxxxxxxxxxx> > > > > wrote: > > > Hello, > > > > > > I'd like to invite everyone to share ideas regarding required encoder > > > features > > > in this separate sub-tree. > > > > > > In general, encoder devices are more complex compared to decoders. So the > > > question I'd like to rise is in what way we define the minimal subset of > > > features to be implemented by the virtio-video. > > > > > > We may look at the following to define the set of features: > > > 1. USB video, 2.3.6 Encoding Unit [1]. > > > 2. Android 10 Compatibility Definition [2]. > > > > > > Would be nice to hear about any specific requirements from the Chromium > > > team as > > > well. > > > > > > [1] https://www.usb.org/sites/default/files/USB_Video_Class_1_5.zip > > > [2] > > > https://source.android.com/compatibility/android-cdd#5_2_video_encoding > > > > > > Thank you. > > > > > > Best regards, > > > Dmitry. > > > > > > On Mittwoch, 4. Dezember 2019 10:16:20 CET Gerd Hoffmann wrote: > > > > Hi, > > > > > > > > > 1. Focus on only decoder/encoder functionalities first. > > > > > > > > > > As Tomasz said earlier in this thread, it'd be too complicated to > > > > > > support > > > > > > > > camera usage at the same time. So, I'd suggest to make it just a > > > > > > generic > > > > > > > > mem-to-mem video processing device protocol for now. > > > > > If we finally decide to support camera in this protocol, we can add it > > > > > later. > > > > > > > > Agree. > > > > > > > > > 2. Only one feature bit can be specified for one device. > > > > > > > > > > I'd like to have a decoder device and encoder device separately. > > > > > It'd be natural to assume it because a decoder and an encoder are > > > > > > provided > > > > > > > > as different hardware. > > > > > > > > Hmm, modern GPUs support both encoding and decoding ... > > > > > > > > I don't think we should bake that restriction into the specification. > > > > It probably makes sense to use one virtqueue per function though, that > > > > will simplify dispatching in both host and guest. > > > > > > > > > 3. Separate buffer allocation functionalities from virtio-video > > > > > > protocol. > > > > > > > > To support various ways of guest/host buffer sharing, we might want to > > > > > have a dedicated buffer sharing device as we're discussing in another > > > > > thread. Until we reach consensus there, it'd be good not to have > > > > > buffer > > > > > allocation > > > > > functionalities in virtio-video. > > > > > > > > I think virtio-video should be able to work as stand-alone device, > > > > so we need some way to allocate buffers ... > > > > > > > > Buffer sharing with other devices can be added later. > > > > > > > > > > +The virtio video device is a virtual video streaming device that > > > > > > supports the +following functions: encoder, decoder, capture, > > > > > > output. > > > > > > + > > > > > > +\subsection{Device ID}\label{sec:Device Types / Video Device / > > > > > > Device > > > > > > > > > ID} > > > > > > + > > > > > > +TBD. > > > > > > > > > > I'm wondering how and when we can determine and reserve this ID? > > > > > > > > Grab the next free, update the spec accordingly, submit the one-line > > > > patch. > > > > > > > > > > +\begin{lstlisting} > > > > > > +enum virtio_video_pixel_format { > > > > > > + VIRTIO_VIDEO_PIX_FMT_UNDEFINED = 0, > > > > > > + > > > > > > + VIRTIO_VIDEO_PIX_FMT_H264 = 0x0100, > > > > > > + VIRTIO_VIDEO_PIX_FMT_NV12, > > > > > > + VIRTIO_VIDEO_PIX_FMT_NV21, > > > > > > + VIRTIO_VIDEO_PIX_FMT_I420, > > > > > > + VIRTIO_VIDEO_PIX_FMT_I422, > > > > > > + VIRTIO_VIDEO_PIX_FMT_XBGR, > > > > > > +}; > > > > > > > > > > I'm wondering if we can use FOURCC instead. So, we can avoid > > > > > > reinventing a > > > > > > > > mapping from formats to integers. > > > > > Also, I suppose the word "pixel formats" means only raw (decoded) > > > > > > formats. > > > > > > > > But, it can be encoded format like H.264. So, I guess "image format" > > > > > or > > > > > "fourcc" is a better word choice. > > > > > > > > Use separate pixel_format (fourcc) and stream_format (H.264 etc.) enums? > > > > > > > > > > +\begin{lstlisting} > > > > > > +struct virtio_video_function { > > > > > > + struct virtio_video_desc desc; > > > > > > + __le32 function_type; /* One of VIRTIO_VIDEO_FUNC_* types */ > > > > > > + __le32 function_id; > > > > > > + struct virtio_video_params in_params; > > > > > > + struct virtio_video_params out_params; > > > > > > + __le32 num_caps; > > > > > > + __u8 padding[4]; > > > > > > + /* Followed by struct virtio_video_capability video_caps[]; > > > > > > */ > > > > > > > > > +}; > > > > > > +\end{lstlisting} > > > > > > > > > > If one device only has one functionality, virtio_video_function's > > > > > > fields > > > > > > > > will be no longer needed except in_params and out_params. So, we'd be > > > > > able to remove virtio_video_function and have in_params and out_params > > > > > > in > > > > > > > > virtio_video_capability instead. > > > > > > > > Same goes for per-function virtqueues (used virtqueue implies function). > > > > > > > > > > +\begin{lstlisting} > > > > > > +struct virtio_video_resource_detach_backing { > > > > > > + struct virtio_video_ctrl_hdr hdr; > > > > > > + __le32 resource_id; > > > > > > + __u8 padding[4]; > > > > > > +}; > > > > > > +\end{lstlisting} > > > > > > + > > > > > > +\begin{description} > > > > > > +\item[\field{resource_id}] internal id of the resource. > > > > > > +\end{description} > > > > > > > > > > I suppose that it'd be better not to have the above series of > > > > > > T_RESOURCE > > > > > > > > controls at least until we reach a conclusion in the thread of > > > > > buffer-sharing device. If we end up concluding this type of controls > > > > > is > > > > > the best way, we'll be able to revisit here. > > > > > > > > Well. For buffer management there are a bunch of options. > > > > > > > > (1) Simply stick the buffers (well, pointers to the buffer pages) into > > > > > > > > the virtqueue. This is the standard virtio way. > > > > > > > > (2) Create resources, then put the resource ids into the virtqueue. > > > > > > > > virtio-gpu uses that model. First, because virtio-gpu needs an id > > > > to reference resources in the rendering command stream > > > > (virtio-video doesn't need this). Also because (some kinds of) > > > > resources are around for a long time and the guest-physical -> > > > > host-virtual mapping needs to be done only once that way (which > > > > I think would be the case for virtio-video too because v4l2 > > > > re-uses buffers in robin-round fashion). Drawback is this > > > > assumes shared memory between host and guest (which is the case > > > > in typical use cases but it is not mandated by the virtio spec). > > > > > > > > (3) Import external resources (from virtio-gpu for example). > > > > > > > > Out of scope for now, will probably added as optional feature > > > > later. > > > > > > > > I guess long-term we want support either (1)+(3) or (2)+(3). > > > > > > > > cheers, > > > > > > > > Gerd > > > > > > --------------------------------------------------------------------- > > > To unsubscribe, e-mail: virtio-dev-unsubscribe@xxxxxxxxxxxxxxxxxxxx > > > For additional commands, e-mail: virtio-dev-help@xxxxxxxxxxxxxxxxxxxx > >
