[FFmpeg-devel] [PATCH]lavf/mov: Support alac extradata in wave atom

Carl Eugen Hoyos cehoyos at ag.or.at
Mon Aug 3 12:32:02 CEST 2015

Paul B Mahol <onemda <at> gmail.com> writes:

> > Attached patch fixes ticket #4747 for me, 

> > I don't know how to detect that the wave 
> > atom contains no frma / alac atom...
> And that is mentioned because?

The file from ticket #4747 does not contain an 
alac atom which is required for alac decoding. 
Instead it contains the necessary data in the 
wave atom (where you normally would find the 
alac atom). To distinguish, it would be 
necessary to look "into" the wave atom to know 
if it contains an alac atom or not.

I meanwhile found that the mpeg demuxer 
sometimes seeks eight bytes back which I will 
probably copy. The alternative, iiuc, would be 
to copy the whole wave atom into a buffer and 
call mov_read_default() from the wave_read() 
function with that buffer.
But this should not be necessary if somebody 
can confirm that it is ok to seek back x bytes 
in a demuxer.

As an alternative the current version could 
also be committed, I am not sure.

Carl Eugen

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