Re: [FFmpeg-devel] [EXT] Re: [PATCH v4 2/3] avcodec/v4l2_context: resume the decoding process after source change event received.

[Ming Qian <ming.qian@nxp.com>]

> -----Original Message-----
> From: Andriy Gelman [mailto:andriy.gelman@gmail.com]
> Sent: Monday, January 3, 2022 12:41 AM
> To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
> Cc: Ming Qian <ming.qian@nxp.com>
> Subject: [EXT] Re: [FFmpeg-devel] [PATCH v4 2/3] avcodec/v4l2_context:
> resume the decoding process after source change event received.
> 
> Caution: EXT Email
> 
> On Thu, 19. Aug 16:55, Ming Qian wrote:
> > client need to resume the decoding process after it dequeues the
> > source change event.
> > no matter what's the return value of v4l2_resolution_changed().
> > if the client doesn't resume the decoding process, the decoder may
> > keep waiting
> >
> > in documentation of v4l2 stateful decoder, we can see the following
> > description:
> >       The client must continue the sequence as described below to
> >       continue the decoding process.
> >       1.  Dequeue the source change event.
> >               Important
> >               A source change triggers an implicit decoder drain,
> >               similar to the explicit Drain sequence. The decoder is
> >               stopped after it completes. The decoding process must be
> >               resumed with either a pair of calls to
> >               VIDIOC_STREAMOFF() and VIDIOC_STREAMON() on the
> CAPTURE
> >               queue, or a call to VIDIOC_DECODER_CMD() with the
> >               V4L2_DEC_CMD_START command.
> >       2.  Continue with the Capture Setup sequence.
> 
> Please also add that this fixes decoding of
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fstreams
> .videolan.org%2Fffmpeg%2Fincoming%2F720p60.mp4&amp;data=04%7C01%
> 7Cming.qian%40nxp.com%7Cea94a9c4cc0643b0a41f08d9ce0eadc5%7C686e
> a1d3bc2b4c6fa92cd99c5c301635%7C0%7C1%7C637767384703207931%7CU
> nknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6
> Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=X4rKQX19MQg1gO3ILiBCQ
> qSLIvqovZLA95KKiyoVNzI%3D&amp;reserved=0 on RPi4.
> 

Hi Andriy,
    What's wrong with this stream? Everything is normal on my side when I play it using ffplay.

> >
> > Signed-off-by: Ming Qian <ming.qian@nxp.com>
> > ---
> >  libavcodec/v4l2_context.c | 52
> > ++++++++++++++++++++++++---------------
> >  1 file changed, 32 insertions(+), 20 deletions(-)
> >
> > diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c
> > index dda5157698c3..b08f0015c2e5 100644
> > --- a/libavcodec/v4l2_context.c
> > +++ b/libavcodec/v4l2_context.c
> > @@ -153,6 +153,21 @@ static inline void
> v4l2_save_to_context(V4L2Context* ctx, struct v4l2_format_upd
> >      }
> >  }
> >
> > +static int v4l2_start_decode(V4L2Context *ctx) {
> > +    struct v4l2_decoder_cmd cmd = {
> > +        .cmd = V4L2_DEC_CMD_START,
> > +        .flags = 0,
> > +    };
> > +    int ret;
> > +
> > +    ret = ioctl(ctx_to_m2mctx(ctx)->fd, VIDIOC_DECODER_CMD, &cmd);
> > +    if (ret)
> > +        return AVERROR(errno);
> > +
> > +    return 0;
> > +}
> > +
> >  /**
> >   * handle resolution change event and end of stream event
> >   * returns 1 if reinit was successful, negative if it failed @@
> > -163,7 +178,7 @@ static int v4l2_handle_event(V4L2Context *ctx)
> >      V4L2m2mContext *s = ctx_to_m2mctx(ctx);
> >      struct v4l2_format cap_fmt = s->capture.format;
> >      struct v4l2_event evt = { 0 };
> > -    int reinit, ret;
> > +    int ret;
> >
> >      ret = ioctl(s->fd, VIDIOC_DQEVENT, &evt);
> >      if (ret < 0) {
> > @@ -185,35 +200,29 @@ static int v4l2_handle_event(V4L2Context *ctx)
> >          return 0;
> >      }
> >
> > -    reinit = v4l2_resolution_changed(&s->capture, &cap_fmt);
> > -    if (reinit) {
> > +    if (v4l2_resolution_changed(&s->capture, &cap_fmt)) {
> >          s->capture.height = v4l2_get_height(&cap_fmt);
> >          s->capture.width = v4l2_get_width(&cap_fmt);
> >          s->capture.sample_aspect_ratio = v4l2_get_sar(&s->capture);
> 
> > +    } else {
> > +        v4l2_start_decode(ctx);
> > +        return 0;
> >      }
> 
> You can minimize the diff just by adding this part and the definition for
> v4l2_start_decode(). Then have a separate commit that cleans up and removes
> the reinit variable.
> 

OK, I'll split it into two parts.

> >
> > -    if (reinit)
> > -        s->reinit = 1;
> > +    s->reinit = 1;
> >
> > -    if (reinit) {
> > -        if (s->avctx)
> > -            ret = ff_set_dimensions(s->avctx, s->capture.width,
> s->capture.height);
> > -        if (ret < 0)
> > -            av_log(logger(ctx), AV_LOG_WARNING, "update avcodec
> height and width\n");
> > +    if (s->avctx)
> > +        ret = ff_set_dimensions(s->avctx, s->capture.width,
> s->capture.height);
> > +    if (ret < 0)
> > +        av_log(logger(ctx), AV_LOG_WARNING, "update avcodec height
> > + and width\n");
> >
> > -        ret = ff_v4l2_m2m_codec_reinit(s);
> > -        if (ret) {
> > -            av_log(logger(ctx), AV_LOG_ERROR,
> "v4l2_m2m_codec_reinit\n");
> > -            return AVERROR(EINVAL);
> > -        }
> > -        goto reinit_run;
> > +    ret = ff_v4l2_m2m_codec_reinit(s);
> > +    if (ret) {
> > +        av_log(logger(ctx), AV_LOG_ERROR, "v4l2_m2m_codec_reinit\n");
> > +        return AVERROR(EINVAL);
> >      }
> >
> > -    /* dummy event received */
> > -    return 0;
> > -
> >      /* reinit executed */
> > -reinit_run:
> >      return 1;
> >  }
> >
> > @@ -551,6 +560,9 @@ int ff_v4l2_context_set_status(V4L2Context* ctx,
> uint32_t cmd)
> >      int type = ctx->type;
> >      int ret;
> 
> >
> > +    if (ctx->streamon == (cmd == VIDIOC_STREAMON))
> > +        return 0;
> > +
> 
> This change looks unrelated.

Yes it is not directly related, it's just an enhancement that avoid driver can't handle the repeated streamon or streamoff ioctl.
Maybe I can remove it from this patch, and make a single patch.

> 
> >      ret = ioctl(ctx_to_m2mctx(ctx)->fd, cmd, &type);
> >      if (ret < 0)
> >          return AVERROR(errno);
> 
> Thanks,
> --
> Andriy
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