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Topic: Frame header of Lame 3.100 file (Read 721 times) previous topic - next topic
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Frame header of Lame 3.100 file

Hi,
I destroyed the LAME tags of numerous mp3s (encoded with Lame 3.100 with option V3) by incorrectly assigning the id3 tag with ffmpeg. Since the LAME tags are almost identical, I was able to determine almost all of the incorrect bytes (mostly 00) using correct files. The only thing I'm not sure about is the frame start FF FB 90 44 or FF FB 90 64: What is the meaning of the fourth octet? In some of the mp3s it is 44, in others it is 64.  :(
Thank you very much!

Re: Frame header of Lame 3.100 file

Reply #2 –
6 is 0110
4 is 0100

Based on http://www.mp3-tech.org/programmer/frame_header.html this is Joint stereo (01) with different "Mode extension (Only used in Joint stereo)". For layer III:
  • 10 - MS stereo on, intensity stereo off
  • 00 - both off

Re: Frame header of Lame 3.100 file

Reply #3 –
Thank you very much, I didn't know about this documentation. But this raises the question of how (and whether) I can find out which mode extension is in the file based on the available data in the mp3.