I was surprised and disappointed to find that the audio channel in a video file made with my M5 is only 128 kb/s. This is adequate for speech but not good enough for anything else. Of course, the quality is only as good as the input and circuitry, but there needs to be as full an output as possible.
My 70D and my 100D both create audio of 48 Mhz, 16 bit PCM - about as good as it gets.
The details are not complete in the specs. I would have been reasonably happy with AAC at, say, 320kb/s, but not 128kb/s but that is not made explicit.
