[FFmpeg-devel] [FFmpeg-cvslog] fftools/ffmpeg: add loopback decoding

[Gyan Doshi]

On 2024-03-14 03:46 pm, Anton Khirnov wrote:
> Quoting Gyan Doshi (2024-03-13 08:49:52)
>
>> Are there any limitations to loopback decoding e.g. would a vpx w/alpha
>> encode be decoded back to a alpha pix fmt?
> I don't know how vpx alpha works, was it a separate stream in the
> demuxer or something like that?

The encoder attaches the coded alpha as side data to the packet. Only a 
couple of containers support this SD.
The demuxer, in turn, attaches the alpha as SD upon export.

> Loopback decoders work exactly like normal decoders, except their
> packets arrive from an encoder instead of a demuxer.
In terms of syntax, do all LB streams have to be specified in the first 
output? Does that output muxer have to be null, or can those packets be 
routed to both output and LB? Regards, Gyan