Skip to main content

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Frame header of Lame 3.100 file (Read 1468 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

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.