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M4A files (Foobar2000/NeroAacEnc) play at double speed

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madsic:
Having searched the forums I came across some advice regarding how to make m4a files that would be compliant with the way Rockbox expects M4A files to be (something about the placements of tags, I think). So I got hold of Foobar2000 and the Nero Aac Encoder that would work with it and set to work.

Now unlike many other M4A/MP4 files that I've tried on Rockbox, this one isn't skipped over but loaded and played. Tag information displays correctly. However playback is very fast (mouse voice). The displayed length of the file is half of what it should be and the 'current position' advances quicker than realtime too. The bitrate displayed is double that which WinAmp report (106 kbps to WAs 53 kbps).

I have seen mention that the m4a codec on some targets (mine is an iPod nano) was not yet at realtime but this is obviously quite another problem. Is this a general thing or something to do with the encoding process? The file plays normally in WinAmp.

Any help appreciated.

Llorean:
Which type of AAC file is it?

madsic:
Not sure what you mean. This is what WinAmp's file info says:


--- Code: ---Track Type Info
1 audio MPEG-4 AAC LC, 4353.479 secs, 53 kbps, 22050 Hz
--- End code ---

Does that help?

Llorean:
Try encoding the file at 44100 Hz instead. There are some resampling issues on iPods.

Lear:
I doubt the resampler is the problem. I suspect it is the SBR detection. In FAAD (I think it was) I found a note to this effect:


--- Quote ---SBR not indicated, but the file might still contain SBR. MPEG specification says that one should assume SBR if samplerate

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