[Mp4-tech] How to find AAC VBR play time

[Faerber Tobias Com MD PD SWC 3 MCH 21]

Hi,
you can start parsing a certain amount of headers before starting playback.
Read the number of bits per frame and build an average bitrate. Then
calculate the song's duration from the average br and the file length.
In ADIF there is a seperate br field in each header.
In ADTS you have the frame length info in the variable header allowing you
also calculating the bitrate in each frame from the length and the number of
samples per frame and the sampling frequency used.
During playback you can then adapt the real length by getting more and more
frames and as such a more and more precise average bitrate information.
The correct indication of course you get by pasing the whole file before
playback. But this might take too much time up-front.
Hope this helped,
BR,
Tobi
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Sanjay N
Sent: Donnerstag, 21. April 2005 02:03
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] How to find AAC VBR play time
Hi,
I am trying to find out AAC VBR stream length (total play time of the stream
in seconds). Can anyone tell me how to do it ? Are there any headers similar
to  'Xing' / 'VBRI' (MP3) in AAC ??
With Warm Regards,
       Sanjay
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