Patch to read disc number in mov.c

[Reuben Thomas]

I attach a patch against current git head to read disc number in mov.c, for example from .m4a files. I used the information at:

​http://atomicparsley.sourceforge.net/mpeg-4files.html

to get the correct atom code and decode the information ('disk' works like 'trkn', so I was able to common up the decoding logic). Note that the tag I fill in is called 'disc', not 'disk', for consistency with the rest of ffmpeg.

The motivation to add this was that multi-disc albums were not sorting correctly in MPD build against libavformat. With this fix it works fine.

I'm very keen to see this fix get into ffmpeg, and this is the first patch I've sent, so if there's anything wrong with it, do say and I'll work to fix it.

[Baptiste Coudurier]

Thanks for the patch !

Change the parse function to take atom tag, and change the code only in parse_trkn

[Reuben Thomas]

Sorry, can you explain a bit more, please? There is no function parse_trkn, and the atom tag is not enough, the key string is needed to pass to av_metadata_set2.

[Reuben Thomas]

OK, I tried to understand the comment above and redid my patch.

[Reuben Thomas]

Hi, please can you review the updated patch? I would like to get this one signed off!

[Reuben Thomas]

(I checked, the patch still applies to git head.)

[Carl Eugen Hoyos]

Pushed.

Thank you for your patience!