[FFmpeg-devel] [EXT] [PATCH 1/2] avcodec/v4l2_context: Drop empty packet while draining

[Andriy Gelman]

On Thu, 30. Apr 01:39, Ming Qian wrote:
> > From: Andriy Gelman <andriy.gelman at gmail.com>
> > 
> > v4l2_m2m devices may send an empty packet/frame while draining to indicate
> > that all capture buffers have been flushed.
> > 
> > Currently, the empty packet/frame is not handled correctly:
> > When encoding, the empty packet is forwarded to the muxer, usually creating
> > warnings.
> > When decoding, a reference to the memory is created anyway.. Since in the
> > past this memory contained a decoded frame, it results in an extra frame being
> > decoded.
> > 
> > This commit discards the empty packet/frame.
> > 
> > References:
> > linux/Documentation/media/uapi/v4l/dev-decoder.rst:
> > 
> >     "The last buffer may be empty (with :c:type:`v4l2_buffer` bytesused = 0)
> >      and in that case it must be ignored by the client, as it does not
> >      contain a decoded frame."
> > 
> > linux/Documentation/media/uapi/media/v4l/vidioc-encoder-cmd.rst:
> > 
> >     "...This buffer may be empty, indicated by the
> >      driver setting the ``bytesused`` field to 0."
> > 
> > Signed-off-by: Andriy Gelman <andriy.gelman at gmail.com>
> > ---
> >  libavcodec/v4l2_context.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c index
> > 6c2db5c849..f0ecc18ebd 100644
> > --- a/libavcodec/v4l2_context.c
> > +++ b/libavcodec/v4l2_context.c
> > @@ -393,6 +393,15 @@ dequeue:
> >              return NULL;
> >          }
> > 
> > +        if (ctx_to_m2mctx(ctx)->draining
> > && !V4L2_TYPE_IS_OUTPUT(ctx->type)) {
> > +            int bytesused = V4L2_TYPE_IS_MULTIPLANAR(buf.type) ?
> > +                            buf.m.planes[0].bytesused : buf.bytesused;
> > +            if (bytesused == 0) {
> > +                ctx->done = 1;
> > +                return NULL;
> > +            }
> > +        }
> > +
> >          avbuf = &ctx->buffers[buf.index];
> >          avbuf->status = V4L2BUF_AVAILABLE;
> >          avbuf->buf = buf;
> > --
> > 2.25.1
> > 

> 
> Lgtm
> 

Thanks. 
Will apply both patches on Friday if no one objects.

-- 
Andriy