MP3 or AAC with CBR issues

Discussion in 'iOS Programming' started by Craigy, Sep 22, 2008.

  1. Craigy macrumors 6502

    Joined:
    Jan 14, 2003
    Location:
    New Zealand
    #1
    We are exporting MP3 and AAC files from Logic Pro / Itunes with a constant bit rate - however when we look at these in the terminal they are showing as having a 0 value for the bytes/packet - therefore the SDK is seeing them as VBR files... Here's an example in the terminal:

    File: introduction.mp3
    File type ID: MPG3
    Data format: 2 ch, 44100 Hz, '.mp3' (0x00000000) 0 bits/channel, 0 bytes/packet, 1152 frames/packet, 0 bytes/frame
    no channel layout.
    estimated duration: 246.000 sec
    audio bytes: 4938188
    audio packets: 9452
    bit rate: 160 bits per second
    packet size upper bound: 1052
    maximum packet size: 523
    audio data file offset: 4096
    optimized

    Tried exporting them as AAC and MP3 using both Logic Pro and iTunes but all output files are showing a bytes/packet value.

    Does anyone know how we can ensure that the CBR files have non 0 values for both bytes/packet and frames/packet?
     
  2. Craigy thread starter macrumors 6502

    Joined:
    Jan 14, 2003
    Location:
    New Zealand
    #2
    More info:

    FO:
    MPEG1 layer 3
    9452 frames
    44100 Hz
    38.281250 frames per second
    246.909388 seconds
    4942284 bytes in file (160.132721 kbps)
    4938188 bytes in MP3 frames (160.000008 kbps) = current bitrate
    36500250 bits of payload data (147.828523 kbps)
    4566717 bytes of payload data (147.964143 kbps)
    33486 bits wasted from partially-full bytes (0.135621 kbps)
    4906989 bytes of MP3 data (158.989143 kbps) = minimum bitrate possible
    31199 bytes of padding (1.010865 kbps)
    4096 bytes outside MP3 frames (0.132713 kbps)
    0 sync errors
    Bitrate distribution:
    160: 5208,4244
    Largest frame uses 6427 bits = 804 bytes = 246.033594 kbps
    Smallest bitrate for CBR is 160
     

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