On 17/05/2011 17:21, Christopher Woods (CustomMade) wrote:
I've been taking some previously downloaded raw AAC files (downloaded with
get_iplayer) and wrapping them as M4As using YAMB. For e.g.:
Randomfile.m4a = 111 MB (116,501,077 bytes)
Randomfile.aac = 111 MB (117,371,538 bytes)
I've observed that consistently the resulting M4As are slightly smaller than
the raw AACs. Is this to be expected? Is it something to do with the way the
stream is muxed? I'm certainly not intentionally altering any aspect of the
file during the M4A creation, so how come the M4As (which one would
logically expect to be slightly larger given the wrapper overhead) end up
being the opposite?
I've noticed this with MP4Box as well. I think it filters out ADTS
frame headers when adding the AAC audio as a track to the MP4 file,
which would account for most of the difference. I would guess YAMB does
likewise.
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