[FFmpeg-user] MOV: "undetermined" as audio track language writes "eng"

[Peter B.]

Hi everyone :)

I have a situation where I would need to encode Quicktime (MOV) files
with ISO639-2 language metadata values "less popular/common" than
usual.  I've also read the related the Quicktime Specs [1,2].

How can I set language to e.g. UND or QAA?


Whenever I try to encode a file e.g. with the language tracks "UND"
(=undetermined) or "QAA" (=reserved for local use), the value written to
the file is "ENG".

Both "und" and "qaa" are proper ISO639-2 codes [3].


In order to rule out syntax issues, I've tried with "ger" (=German) and
"fra" (=French): Both work flawlessly.
I've seen in "libavformat/isom.c" [4], and there's a hardcoded list of
ISO639 codes, but says:
/* deprecated by putting the code as 3*5 bits ASCII */

Sounded to me like this list-limitation is superseded
by"ff_mov_iso639_to_lang", but how do I trigger it to be used?


Grateful for any help :)
Thanks in advance,
Peter B.



Here's commandline and complete, uncut console output to reproduce it:

// ------------------------------
$ ffmpeg -y -f lavfi -i "sine=frequency=1000:duration=1" -c:a pcm_s16le
-metadata:s:a:0 language=qaa delme.mov
// ------------------------------

ffmpeg version N-92314-g323c2cf Copyright (c) 2000-2018 the FFmpeg
developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.10) 20160609
  configuration: --prefix=/usr/local --enable-gpl --enable-nonfree
--enable-version3 --enable-postproc --enable-ffplay --enable-swscale
--enable-avfilter --enable-pthreads --enable-bzlib --enable-zlib
--enable-decoder=png --enable-encoder=png --samples=../fate-suite
--enable-libfreetype --enable-libopenjpeg --disable-decoder=jpeg2000
--enable-libvpx --enable-libvorbis --enable-libx264 --enable-libx265
  libavutil      56. 21.100 / 56. 21.100
  libavcodec     58. 34.100 / 58. 34.100
  libavformat    58. 19.102 / 58. 19.102
  libavdevice    58.  4.106 / 58.  4.106
  libavfilter     7. 39.100 /  7. 39.100
  libswscale      5.  2.100 /  5.  2.100
  libswresample   3.  2.100 /  3.  2.100
  libpostproc    55.  2.100 / 55.  2.100
Input #0, lavfi, from 'sine=frequency=1000:duration=1':
  Duration: N/A, start: 0.000000, bitrate: 705 kb/s
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, mov, to 'delme.mov':
  Metadata:
    encoder         : Lavf58.19.102
    Stream #0:0(qaa): Audio: pcm_s16le (sowt / 0x74776F73), 44100 Hz,
mono, s16, 705 kb/s
    Metadata:
      encoder         : Lavc58.34.100 pcm_s16le
[Parsed_sine_0 @ 0x2a09580] EOF timestamp not reliable
size=      87kB time=00:00:01.00 bitrate= 711.1kbits/s speed= 304x   
video:0kB audio:86kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 0.777778%


// ------------------------------
$ ffprobe-git -loglevel quiet -show_entries
stream=index,codec_name,codec_type:stream_tags=language -i delme.mov
// ------------------------------
[STREAM]
index=0
codec_name=pcm_s16le
codec_type=audio
TAG:language=eng
[/STREAM]



// ------------------------------
$ ffmpeg-git -y -f lavfi -i "sine=frequency=1000:duration=1" -c:a
pcm_s16le -metadata:s:a:0 language=ger delme.mov
// ------------------------------

ffmpeg version N-92314-g323c2cf Copyright (c) 2000-2018 the FFmpeg
developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.10) 20160609
  configuration: --prefix=/usr/local --enable-gpl --enable-nonfree
--enable-version3 --enable-postproc --enable-ffplay --enable-swscale
--enable-avfilter --enable-pthreads --enable-bzlib --enable-zlib
--enable-decoder=png --enable-encoder=png --samples=../fate-suite
--enable-libfreetype --enable-libopenjpeg --disable-decoder=jpeg2000
--enable-libvpx --enable-libvorbis --enable-libx264 --enable-libx265
  libavutil      56. 21.100 / 56. 21.100
  libavcodec     58. 34.100 / 58. 34.100
  libavformat    58. 19.102 / 58. 19.102
  libavdevice    58.  4.106 / 58.  4.106
  libavfilter     7. 39.100 /  7. 39.100
  libswscale      5.  2.100 /  5.  2.100
  libswresample   3.  2.100 /  3.  2.100
  libpostproc    55.  2.100 / 55.  2.100
Input #0, lavfi, from 'sine=frequency=1000:duration=1':
  Duration: N/A, start: 0.000000, bitrate: 705 kb/s
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, mov, to 'delme.mov':
  Metadata:
    encoder         : Lavf58.19.102
    Stream #0:0(ger): Audio: pcm_s16le (sowt / 0x74776F73), 44100 Hz,
mono, s16, 705 kb/s
    Metadata:
      encoder         : Lavc58.34.100 pcm_s16le
[Parsed_sine_0 @ 0x2998580] EOF timestamp not reliable
size=      87kB time=00:00:01.00 bitrate= 711.1kbits/s speed= 357x   
video:0kB audio:86kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 0.777778%


// ------------------------------
$ ffprobe -loglevel quiet -show_entries
stream=index,codec_name,codec_type:stream_tags=language -i delme.mov
// ------------------------------
[STREAM]
index=0
codec_name=pcm_s16le
codec_type=audio
TAG:language=ger
[/STREAM]




== References:
[1]
https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap2/qtff2.html
[2]
https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap4/qtff4.html#//apple_ref/doc/uid/TP40000939-CH206-35103
[3] https://en.wikipedia.org/wiki/List_of_ISO_639-2_codes
[4] https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/isom.c