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

[Ming Qian]

> 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