If m4a is the same as mp4 (minus the video), then how is it that doing
ffmpeg -i old.m4a new.mp4
Reduces file size so much? I am using the default settings.
Why does ffmpeg m4a → mp4 reduce file size by 60% if they are the same?
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1 Answers
That command will re-encode all streams, in which case, the result can be smaller or larger than the source, since the default encoding parameters may be smaller or larger than the source parameters.
To simply transfer source streams to destination, you have to enable streamcopying. To do that, add -c copy (-c is short for -codec)
ffmpeg -i old.m4a -c copy new.mp4
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