[FFmpeg-user] Naming an audio track

Moritz Barsnick barsnick at gmx.net
Mon Nov 3 12:12:21 CET 2014


[Replying to self]
On Mon, Nov 03, 2014 at 10:21:39 +0100, Moritz Barsnick wrote:
> I do not know, though, whether "name" is a header such as "stco" or
> "udta".

So apparently we're looking as MPEG4/MOV containers here. That's what
Tomáš was using as well, and where I managed to reproduce.

Using AtomicParsley, I managed to "see" that the tag in use is an atom
trak.udta.name:

     Atom trak @ 8193 of size: 560, ends @ 8753
         Atom tkhd @ 8201 of size: 92, ends @ 8293
         Atom mdia @ 8293 of size: 428, ends @ 8721
             [...]
         Atom udta @ 8721 of size: 32, ends @ 8753
             Atom name @ 8729 of size: 24, ends @ 8753

The atom is described here:
https://developer.apple.com/library/mac/documentation/QuickTime/QTFF/QTFFChap2/qtff2.html#//apple_ref/doc/uid/TP40000939-CH204-BBCCFFGD

I have found a mention that HandBrake and subler use this atom:
https://github.com/pjan/osx-dotfiles/blob/55d452fae4037a019c85a6095a5b3a0bd11e3d15/.dotfiles/.encode-handheld.pl#L2907

I couldn't figure how to add arbitrary atoms with AtomicParsley, only
how to delete them. I do see ffmpeg has a function named
mov_write_track_udta_tag(), called from mov_write_trak_tag(), called
from mov_write_moov_tag(), but I don't know if it gets used and whether
it does the "right thing" from VLC's point of view, and how to get it
to write the "right thing".

Getting closer,
Moritz

P.S.: Interesting, because it follows a question I never dared to ask:
      Where does my PVR/STB get the names of its audio tracks from?
      (Albeit MPEG-TS.)


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