[FFmpeg-devel] Please, clarify -r/-fps_mode usage for YUV encoding

[Rogozhkin, Dmitry V]

On Wed, 2023-03-15 at 21:52 +0100, Timo Rothenpieler wrote:
> On 15.03.2023 21:36, Rogozhkin, Dmitry V wrote:
> > Hi,
> > 
> > Can someone, please, help to clarify ffmpeg behavior after one of
> > the
> > recent changes [1]. This commit turns warning into error to prevent
> > usage of conflicting options. Error printed out is:
> > “One of -r/-fpsmax was specified together a non-CFR -vsync/-
> > fps_mode.
> > This is contradictory.”
> > 
> > In our command lines [2] we were using -fps_mode passthrough to
> > make
> > sure that there is no frame rate conversion/frame dropping which is
> > desirable for quality benchmarking use case. We did not use -r
> > option
> > for any transcoding use cases. However, we did use -r for YUV
> > encoding
> > use cases along with -fps_mode passthrough, i.e. command lines were
> > looking like:
> > 
> > ffmpeg <...>  \
> >    -f rawvideo -pix_fmt yuv420p -s:v ${w}x${h} -r $framerate -i
> > $yuv \
> >    -c:v h264_qsv <...> -fps_mode passthrough -y $output
> > 
> > Above YUV encoding command line continues to work after [1] without
> > warnings or errors. My understanding is that in case of YUV -r
> > specifies a framerate of the input YUV file while for transcoding
> > case
> > -r actually overrides framerate of the input bitstream and causes
> > frame
> > rate conversion per se which clearly conflicts with intend of
> > -fps_mode
> > passthrough which specifies that the frame rate is “passing
> > through”
> > without conversion. Thus, using -r along with -fps_mode passthrough
> > is
> > a valid for YUV encoding (since fps_mode will be the only frame
> > rate
> > conversion being requested), but that’s not a valid combination for
> > transcoding use cases. Is this interpretation correct?
> > 
> > [1]
> > https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/260f3918937463f1b90e1b77cba80b917f3cb8c1
> > [2] 
> > https://github.com/intel/media-delivery/blob/master/doc/quality.rst
> > 
> > Regards,
> > Dmitry.
> 
> The option to specify the framerate of a rawvideo input is
> -framerate:
> https://ffmpeg.org/ffmpeg-formats.html#rawvideo
> 
> With -r you're telling ffmpeg to overwrite the framerate of the
> input, 
> which probably defaults to 24 or something.
> And then you also tell it to not mess with the framerate which, as
> it 
> correctly points, out is contradictory.

Thank you for quick reply. This makes sense now. We will make a fix on
our side.

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