[FFmpeg-devel] [PATCH 2/3] avformat: Support s337m in mxf/wav/w64

[Gaullier Nicolas]

> > > MXF has a UL registered for Dolby-E:
> I also notice this UL is already in mxf.c, but added commented out by Baptiste back in 2006..
There are two ways for signalling dolby-E in MXF : channel status IF using an AES3 descriptor, or the registered UL for Sound Essence Coding.
ARD/ZDF/HDF requires both but it is very specific. The use of the channel status only seems a little bit more common, I have seen it in Harmonic files.
But at the end, what is really highly widespread is to have no signaling at all.

> So, a general solution is needed. When the user knows the audio is Dolby-E then they can obviously just override the decoder, if they want (not always). Another typical case is "if you think the audio is Dolby- E, automatically decode it so I don't blow my speakers!". An option could allow avformat_find_stream_info() to wait for the first audio packet and probe it, and not take what the demuxer says at face value.
Concerning a general solution, the problem is even worse : nowadays MXF files are mostly structured with mono audio tracks (ARD/ZDF, AS-10 in France etc.)...
My idea was to enable the submux only for wav/mxf/potentially quicktime because I don't see use case for other formats; but this require stereo audio.
For a more general solution (MXF with mono audio tracks specifically), I have in mind to build an audio filter : a graph would merge the L/R to build a dolbyE stream that the filter could decode: this is not very handy for users, but I don't know how it could be done otherwise.
I am currently working with an AVOption in MXF&WAV contexts, but if you think avformat_find_stream_info() is a better way, I will take a look... but I am not very confident with my knowledge of ffmpeg for that work, and I will rather certainly concentrate on the general case with the audio filter if this is valid for you ?

Thank you for all your comments
Nicolas