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

[Anton Khirnov <anton@khirnov.net>]

Quoting Marton Balint (2023-12-08 00:11:21)
> Wipe reminds me of the wipe effect. How about 'predecode_clear'?

Fine with me I guess.

> >
> >> + */
> >> +#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?
> 
> Lack of error checking is intentional. av_image_fill_color might not 
> support all pixel formats, definitely not support hwaccel formats. It 
> might make sense to warn the user once, but I don't think propagating the 
> error back is needed here.
> 
> I primarily thought of this as a QC feature (even thought about making the 
> color fill green by default to make it more noticeable (YUV green happens 
> to be 0,0,0), but for that I'd need similar checks for colorspaces to 
> what I have for fill_black())...

As Mark said, I expect people to want to use it as a security feature.
So either it should work reliably, or it should be made very clear that
it's for debugging only.

For non-hwaccel pixel formats, you can fall back on memsetting the
buffer to 0.

-- 
Anton Khirnov
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