[FFmpeg-devel] [PATCH 0/6] Toward a SPS filter for H.264

[Vittorio Giovara]

On 30/11/2014 01:45, Christophe Gisquet wrote:
> Most of the code is actually not mine but originated from "Direct264":
> http://forum.doom9.org/showthread.php?t=152419
> https://svn.code.sf.net/p/direct264/code/Patches/
> Therefore I've tried to split as best as possible the code I have added.
> There are 3 controversial parts in this patch set:
> - the BSF API change (fixing it is out of my league/time budget)
> - the filter doing in-place filtering (?)
> - the level of validation for this new filter
>
> I've only tested the cropping feature, and validating that the rest
> works tenuous. Anyway, cropping is unfortunately not at all well
> supported:
> - VLC 2.1.5 (Windows) either crashes or outputs garbage
> - DXVA on some Intel core gets top/left cropping completely wrong
>    (0,0 but something valid for bottom/right seems to be OK)
> - ffmpeg-based decoders (e.g. mplayer) are OK
>
> It is possible the implementation is incorrect but it was written
> following the specs.
>
I don't really understand this patchset nor the usecase for it.
While of course it's technically possible to change the SPS, it's a 
VeryBadIdea to so. Especially if you are targetting cropping (which is 
fixed in VLC 2.2 btw), you *never ever* have to ignore it, but use it to 
crop the picture correctly, as it's a mandatory part in the H264 
specifications. If your use case is non-spec compliant, then you already 
have a CODEC_FLAG for that, which does not modifies the bitstream.
All other uses cases seem workaround for broken encoders/decoders, it'd 
be better to fix those instead.

Vittorio