[Mp4-tech] Re: AAC LTP conformace files: Invalid MP4 headers?

Thu Sep 11 19:53:08 EDT 2003

Dear Eddie,
thanks for this valuable information. We can confirm your observataion 
(moov.trak.mdia.mdhd.timescale is 3) as well as your conclusion (it should be 
48000). Most likely, the generator has provided the sampling_frequency_index 
instead of the sampling frequency. We observed that some related fields 
(moov.mvhd.duration, moov.track.tkhd.duration equals 144384000) are also wrong 
(should be 9024), but consistent with the wrong timescale. We are going to fix this.
Best regards,
Ralph
Eddie Choy wrote:
> Hello all,
> 
> We downloaded the latest AAC LTP conformance bitstreams from  
> _ftp://mpaudconf:[email protected]/mpeg4audio-conformance_, namely 
> ap01_48.mp4, ap02_48.mp4, ap03_48.mp4, ap04_48.mp4 and ap05_48.mp4.  We 
> noticed that the "timescale" field in the "mdhd" atom contains the value 
> "3" in all these files.  This is not quite correct as these files are at 
> 48 kHz (sampling rate) and this field should have been set to 48000.  
> Does anybody notice this problem?
> 
> Regards,
> Eddie
> 
> 
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