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Why do many audio players interpret my mono AAC (m4a) files as stereo?

HomeCategory: stackoverflowWhy do many audio players interpret my mono AAC (m4a) files as stereo?
Avatarrupesh asked 5 months ago

In my iPhone app I record audio files in AAC (m4a container) in mono using AVAudioRecorder, i.e. I explicitly set

[recordSettings setValue:[NSNumber numberWithInt: 1] forKey:AVNumberOfChannelsKey];

When opening those files in audio editors like Audacity they only show one channel as expected. However, there are many popular audio players like VLC or foobar2000 that interpret the file as stereo. E.g. when I display the Media Information... > Codec Details in VLC it looks like this:

Screenshot VLC

Interestingly, files recorded with Apple’s Voice Memo app on the iPhone show the same behavior. They appear to be stereo files in several audio players but when I open them in Audacity it turns out they only have one channel.

I cannot believe that all those well-known media players are buggy. So is there some way to tell AVAudioRecorder to set the channel number in a way so that all major media players can detect it properly?

1 Answers
Best Answer
AvatarMatthias answered 5 months ago
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