[FFmpeg-devel] [PATCH 2/2] ffmpeg: Use the colour properties from the input stream when doing transcode

[Xiang, Haihao]

On Wed, 2018-05-23 at 03:27 +0200, Michael Niedermayer wrote:
> On Mon, May 21, 2018 at 11:07:34PM +0100, Mark Thompson wrote:
> > On 16/05/18 08:19, Haihao Xiang wrote:
> > > In lavc/hevec_vaapi, colour properties in AVCodecContext are needed to
> > > write the sequence header
> > > 
> > > Tested by the command below:
> > > ffmpeg -hwaccel vaapi -hwaccel_device /dev/dri/renderD128
> > > -hwaccel_output_format vaapi -i input-with-hdr.mkv -c:v hevc_vaapi
> > > -profile:v main10 output.h265
> > > 
> > > Signed-off-by: Haihao Xiang <haihao.xiang at intel.com>
> > > ---
> > >  fftools/ffmpeg.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> > > index 5a19a09d9a..80b5441f8f 100644
> > > --- a/fftools/ffmpeg.c
> > > +++ b/fftools/ffmpeg.c
> > > @@ -3298,6 +3298,10 @@ static int init_output_stream_encode(OutputStream
> > > *ost)
> > >          dec_ctx = ist->dec_ctx;
> > >  
> > >          enc_ctx->chroma_sample_location = dec_ctx-
> > > >chroma_sample_location;
> > > +        enc_ctx->color_range            = dec_ctx->color_range;
> > > +        enc_ctx->color_primaries        = dec_ctx->color_primaries;
> > > +        enc_ctx->color_trc              = dec_ctx->color_trc;
> > > +        enc_ctx->colorspace             = dec_ctx->colorspace;
> > >      } else {
> > >          for (j = 0; j < oc->nb_streams; j++) {
> > >              AVStream *st = oc->streams[j];
> > > 
> > 
> > There are outstanding patches passing color_range through the filter chain
> > (see <https://lists.ffmpeg.org/pipermail/ffmpeg-devel/2018-May/229248.html>)
> > , and that would be the right solution for the rest of these properties as
> > well, but it would require significantly more work.
> > 
> > I think hacking it like this is ok for now?  It's not worse than before
> > since a change during filtering wasn't visible anyway, and the manual
> > options do still work to override it.  I think the commit message could be a
> > little clearer about the problem (really, that this colour information
> > doesn't pass through filtering) and its limitations (requires a single input
> > matched to the output; will write the wrong thing if filtering changes
> > anything) though, or maybe that could be explained in a comment.
> > 
> > Does anyone else have any thoughts on this?  If there are no objections then
> > I would apply it updated with a clearer explanation.
> 
> I think the key question is
> Does this change "Unknown" to incorrect values

Do you mean the color in dec_ctx may be incorrect? If so, we should fix the
decoder. 

BTW I didn't see error when ran fate test on my machine.
 

> if so it is IMHO not a good idea as we would create broken files where we did
> previously just create files that lacked some metadata
> 
> 
> [...]
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