[FFmpeg-devel] [PATCH 0/5] replace scale2ref by scale=rw:rh

[Niklas Haas]

On Wed, 24 Apr 2024 12:51:55 +0200 Niklas Haas <ffmpeg at haasn.xyz> wrote:
> As discussed in my previous series for fixing scale2ref[1], this filter
> is fundamentally broken, and the only real fix would be to switch to
> activate(), or ideally FFFrameSync.
> 
> [1] https://ffmpeg.org//pipermail/ffmpeg-devel/2024-March/323382.html
> 
> The main thing making this difficult is the fact that scale2ref also
> wants to output ref frames to its secondary output, which FFFrameSync
> does not support, and which is ultimately at least part of the root
> cause of trac #10795.
> 
> Since this is in principle completely unnecessary (users can just
> 'split' the ref input and have it be consumed by vf_scale), and to make
> the design of this filter a bit more robust and maintainable, switch to
> an approach where vf_scale itself gains the ability to reference
> a secondary input stream, using the "ref_*" series of variables.
> 
> This makes the current [i][ri]scale2ref[o][ro] equivalent to the only
> slightly more verbose [ri]split[t][ro]; [i][t]scale=rw:rh[o]. (And
> conversely, it is no longer necessary to use nullsink to consume an
> unused [ro])
> 
> Incidentally, I think it would be nice if lavfi could *automatically*
> split filter links referenced multiple times, so we could just write
> e.g. [i][ri]scale=rw:rh[o]; [ri][o]overlay[out] and have it work. Maybe
> I'll try getting that to work, next.
> 
> Either way, after the deprecation period has elapsed, we can delete
> scale2ref from the codebase in order to make vf_scale.c IMHO
> significantly simpler versus the status quo.
> 
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Will merge in around 24h if there is no objection, as this is fixing
a bug marked important.