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Apologies if this is off topic here.

I have dozens of small audio files recorded using iOS VoiceMemo. These files fail to load properly in a web-based experiment that I am trying to run.

When I open the file in Audacity and then export it as .m4a the file then loads.

When I use ffmpeg -i file.m4a -ss 0.0 -copy newfile.m4a the file still doesn't load.

I'd really like to be able to fix all the files using ffmpeg rather than opening each one at a time in Audacity. From what I understand, Audacity is using ffmpeg to do the export.

How can I get ffmpeg to create a file in the same way that the Audacity export is?

The files can be found here:

File 100.m4a fails to load. File aud100m4a exported via Audacity loads. File ff100.m4a copied using ffmpeg fails to load.

https://github.com/amunn/junk

A link to the test HTML code is here:

https://amunn.github.io/junk/

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The original memo file is encoded as alac :

$ mediainfo 100.m4a 
General
Complete name                            : Téléchargements/100.m4a
Format                                   : MPEG-4
Format profile                           : Apple audio with iTunes info
Codec ID                                 : M4A  (M4A /isom/mp42)
File size                                : 164 KiB
Duration                                 : 3 s 900 ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 344 kb/s
Track name                               : 100
Encoded date                             : UTC 2022-06-10 00:59:40
Tagged date                              : UTC 2022-06-10 00:59:48
Writing application                      : com.apple.VoiceMemos (Jingying's iPhone (null))
voice-memo-uuid                          : 3137F094-78C9-4024-926D-F173E4B35A35

Audio
ID                                       : 1
Format                                   : ALAC
Codec ID                                 : alac
Codec ID/Info                            : Apple Lossless Audio Codec
Duration                                 : 3 s 900 ms
Source duration                          : 3 s 925 ms
Bit rate mode                            : Variable
Bit rate                                 : 339 kb/s
Channel(s)                               : 1 channel
Sampling rate                            : 48.0 kHz
Bit depth                                : 16 bits
Stream size                              : 161 KiB (99%)
Source stream size                       : 161 KiB (99%)
Title                                    : Core Media Audio
Encoded date                             : UTC 2022-06-10 00:59:40
Tagged date                              : UTC 2022-06-10 00:59:48

The audacity export has been transcoded to aac-lc

$ mediainfo Téléchargements/aud100.m4a 
General
Complete name                            : Téléchargements/aud100.m4a
Format                                   : MPEG-4
Format profile                           : Apple audio with iTunes info
Codec ID                                 : M4A  (isom/iso2)
File size                                : 94.4 KiB
Duration                                 : 3 s 370 ms
Overall bit rate mode                    : Constant
Overall bit rate                         : 230 kb/s
Track name                               : 100
Writing application                      : Lavf55.33.100

Audio
ID                                       : 1
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 3 s 370 ms
Duration_LastFrame                       : -1 ms
Bit rate mode                            : Constant
Bit rate                                 : 226 kb/s
Channel(s)                               : 1 channel
Channel layout                           : C
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 93.1 KiB (99%)
Default                                  : Yes
Alternate group                          : 1

and the ffmpeg output has the same codec than the original file :

$ mediainfo Téléchargements/ff100.m4a 
General
Complete name                            : Téléchargements/ff100.m4a
Format                                   : MPEG-4
Format profile                           : Apple audio with iTunes info
Codec ID                                 : M4A  (M4A /isom/iso2)
File size                                : 162 KiB
Duration                                 : 3 s 926 ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 339 kb/s
Track name                               : 100
Writing application                      : Lavf59.16.100

Audio
ID                                       : 1
Format                                   : ALAC
Codec ID                                 : alac
Codec ID/Info                            : Apple Lossless Audio Codec
Duration                                 : 3 s 926 ms
Bit rate mode                            : Variable
Bit rate                                 : 337 kb/s
Channel(s)                               : 1 channel
Sampling rate                            : 48.0 kHz
Bit depth                                : 16 bits
Stream size                              : 161 KiB (99%)
Title                                    : Core Media Audio
Default                                  : Yes
Alternate group                          : 1

I would think that the alac codec is not readable by your web browser and if you want to use ffmpeg you must explicitly ask for a transcoding, as an example :

$ ffmpeg -i 100.m4a -c:a aac anotherff100.m4a
ffmpeg version 4.2.7-0ubuntu0.1 Copyright (c) 2000-2022 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.4.0-1ubuntu1~20.04.1)
  configuration: --prefix=/usr --extra-version=0ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '100.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 0
    compatible_brands: M4A isommp42
    creation_time   : 2022-06-10T00:59:40.000000Z
    title           : 100
    voice-memo-uuid : 3137F094-78C9-4024-926D-F173E4B35A35
    encoder         : com.apple.VoiceMemos (Jingying's iPhone (null))
  Duration: 00:00:03.90, start: 0.000000, bitrate: 343 kb/s
    Stream #0:0(und): Audio: alac (alac / 0x63616C61), 48000 Hz, mono, s16p, 336 kb/s (default)
    Metadata:
      creation_time   : 2022-06-10T00:59:40.000000Z
      handler_name    : Core Media Audio
Stream mapping:
  Stream #0:0 -> #0:0 (alac (native) -> aac (native))
Press [q] to stop, [?] for help
Output #0, ipod, to 'anotherff100.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 0
    compatible_brands: M4A isommp42
    voice-memo-uuid : 3137F094-78C9-4024-926D-F173E4B35A35
    title           : 100
    encoder         : Lavf58.29.100
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp (16 bit), 69 kb/s (default)
    Metadata:
      creation_time   : 2022-06-10T00:59:40.000000Z
      handler_name    : Core Media Audio
      encoder         : Lavc58.54.100 aac
size=      35kB time=00:00:03.90 bitrate=  73.1kbits/s speed= 123x    
video:0kB audio:33kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 4.601811%
[aac @ 0x56201bd0d580] Qavg: 120.461
$ mediainfo anotherff100.m4a 
General
Complete name                            : anotherff100.m4a
Format                                   : MPEG-4
Format profile                           : Apple audio with iTunes info
Codec ID                                 : M4A  (isom/iso2)
File size                                : 34.9 KiB
Duration                                 : 3 s 922 ms
Overall bit rate mode                    : Constant
Overall bit rate                         : 72.8 kb/s
Track name                               : 100
Writing application                      : Lavf58.29.100

Audio
ID                                       : 1
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 3 s 922 ms
Duration_LastFrame                       : -4 ms
Bit rate mode                            : Constant
Bit rate                                 : 69.6 kb/s
Channel(s)                               : 1 channel
Channel layout                           : C
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 33.3 KiB (96%)
Title                                    : Core Media Audio
Default                                  : Yes
Alternate group                          : 1

That might require some tuning to achieve the desired quality output.

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  • 1
    Thank you so much! Audio files are simply a means to an end for me, and I know almost nothing about the huge variety of encodings out there. And the ffmpeg documentation is not too easy to digest. Thanks also for showing the mediainfo tool. Very useful!
    – Alan Munn
    Commented Jul 18, 2022 at 18:34

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