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I am trying to create M4A files to play in my car, which has a USB interface.
This file works fine as is. However if I remux the file using:

ffmpeg -i Miaow-02-Hidden.m4a -c copy outfile.m4a

It will no longer play in my car.

Zombo
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1 Answers1

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I can the two files through TagEditor and noticed a difference:

$ tageditor --info --files Miaow-02-Hidden.m4a outfile.m4a
Technical information for "Miaow-02-Hidden.m4a":
  Container format: MPEG-4 Part 14
    Document type                 M4A
    Duration                      4 min 5 s 156 ms
    Creation time                 2010-11-03 09:42:53
    Modification time             2010-11-03 09:43:12
    Tag position                  before data
    Index position                before data
    Padding                       3.12 KiB

Technical information for "outfile.m4a":
  Container format: MPEG-4 Part 14
    Document type                 M4A
    Version                       512
    Duration                      4 min 5 s 157 ms
    Creation time                 1904-01-01 00:00:00
    Modification time             1904-01-01 00:00:00
    Tag position                  after data
    Index position                after data
    Padding                       8 bytes

As you can see, the original file has the index (moov atom) at the beginning of the file. This is known as faststart. I changed my command and it fixed the problem:

ffmpeg -i Miaow-02-Hidden.m4a -c copy -movflags faststart outfile.m4a
Zombo
  • 1