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While converting audio files from *.m4a to *.wav using ffmpeg (and other audio converters - I've tried a few and cannot remember but they were worse) the file size increases by a lot (10x).

original file (Song01.m4a) 3,425KB

new file (Song01.wav) 38,057KB

Is this an issue specific to the software? Is this as issue dependent on the codecs converting from/to? What can is the best path to get the audio conversion smaller? (assuming I do not plan on converting back)

Additional context: Windows 10, Cygwin (mintty 1.1.3), ffmpeg version

  • I think a lot of the file size increase just comes from converting the file to a .wav extension. .m4a is an apple lossless encoder. I know that an .m4a is way smaller than an .mp3 in size and an .mp3 is smaller than a .wav in size so I would think that most of the jump in file size simply comes from converting to a .wav extension. – user2676140 Jul 9 '16 at 22:14
  • That was my original guess, but I did not know enough about audio codecs/file types to be sure. – Pyker Jul 9 '16 at 22:40
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Converting from M4A to WAV changes from a compressed format to an uncompressed format. M4A uses Advanced Audio Coding (AAC) compression, which is lossy. WAV is uncompressed using Pulse Code Modulation and it is lossless.

The 10-fold increase in the size of your files happens because AAC is compressed audio and Pulse Code Modulation audio is uncompressed. The specific software is not the reason for the larger WAV files. You're right, the size of the converted file depends on the codecs used for the source and target files.

To make smaller files, don't use an uncompressed codec that uses Pulse Code Modulation, so WAV is not a good choice if you want small files.

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