[FFmpeg-devel] [PATCH v2 7/7] avcodec: add AV_CODEC_FLAG_CLEAR

[Anton Khirnov]

Quoting Marton Balint (2023-12-06 09:22:20)
> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  doc/APIchanges             |  3 +++
>  doc/codecs.texi            | 14 ++++++++++++++
>  libavcodec/avcodec.h       |  4 ++++
>  libavcodec/decode.c        |  6 ++++++
>  libavcodec/options_table.h |  1 +
>  libavcodec/version.h       |  2 +-
>  6 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/APIchanges b/doc/APIchanges
> index 416e2bec5e..f839504a64 100644
> --- a/doc/APIchanges
> +++ b/doc/APIchanges
> @@ -2,6 +2,9 @@ The last version increases of all libraries were on 2023-02-09
>  
>  API changes, most recent first:
>  
> +2023-12-xx - xxxxxxxxxxx - lavc 60.36.100 - avcodec.h
> +  Add AV_CODEC_FLAG_CLEAR.

I'm not a huge fan of calling it just 'clear'. How about something more
descriptive like 'wipe_frames'.
> +
>  2023-12-xx - xxxxxxxxxxx - lavu 58.33.100 - imgutils.h
>    Add av_image_fill_color()
>  
> diff --git a/doc/codecs.texi b/doc/codecs.texi
> index 5b950b4560..0504a535f2 100644
> --- a/doc/codecs.texi
> +++ b/doc/codecs.texi
> @@ -76,6 +76,20 @@ Apply interlaced motion estimation.
>  Use closed gop.
>  @item output_corrupt
>  Output even potentially corrupted frames.
> + at item clear
> +Clear the contents of the video buffer before decoding the next picture to it.
> +
> +Usually if only a part of a picture is affected by a decode error then the
> +decoder (if it implements error concealment) tries to hide it by interpolating
> +pixels from neighbouring areas or in some cases from the previous frame. Even
> +without error concealment it is quite likely that the affected area will
> +contain pixels from an earlier frame, due to frame pooling.
> +
> +For quality checking this might not be desirable, because it makes the errors
> +less noticable. By using this flag, and combining it with disabled error
> +concealment (@code{-ec 0}) it is possible to ensure that no leftover data from
> +an earlier frame is presented in areas affected by decode errors.
> +
>  @end table
>  
>  @item time_base @var{rational number}
> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> index 7fb44e28f4..97848e942f 100644
> --- a/libavcodec/avcodec.h
> +++ b/libavcodec/avcodec.h
> @@ -312,6 +312,10 @@ typedef struct RcOverride{
>   * loop filter.
>   */
>  #define AV_CODEC_FLAG_LOOP_FILTER     (1 << 11)
> +/**
> + * Clear frame buffer contents before decoding.

Clear the contents of each frame buffer after it is allocated with
AVCodecContext.get_buffer2() and before anything is decoded into it.

Note that this may have a significant performance cost.

> + */
> +#define AV_CODEC_FLAG_CLEAR           (1 << 12)
>  /**
>   * Only decode/encode grayscale.
>   */
> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> index 2cfb3fcf97..f9b18a2c35 100644
> --- a/libavcodec/decode.c
> +++ b/libavcodec/decode.c
> @@ -1675,6 +1675,12 @@ FF_ENABLE_DEPRECATION_WARNINGS
>  
>      validate_avframe_allocation(avctx, frame);
>  
> +    if (avctx->flags & AV_CODEC_FLAG_CLEAR && avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
> +        uint32_t color[4] = {0};
> +        ptrdiff_t linesize[4] = {frame->linesize[0], frame->linesize[1], frame->linesize[2], frame->linesize[3]};
> +        av_image_fill_color(frame->data, linesize, frame->format, color, frame->width, frame->height);

Should this check for errors?

-- 
Anton Khirnov