Bitrates don't add up (literally)

Discussion in 'Apple TV and Home Theater' started by AdrianK, May 2, 2011.

  1. AdrianK macrumors 68020

    Joined:
    Feb 19, 2011
    #1
    If I understand correctly, the total bitrate should be the sum of the bitrates of all streams, in this case 3820kb/s in total (from 3500+160+80+80). However, the total bitrate is shown as 4142kb/s, so there's a 322kb/s unaccounted for.

    Or is 3500kb/s just the target bitrate, so the resultant bitrate could be higher or lower than the target?

    Here's a full Media Info report, if that helps.
     
  2. roidy macrumors 6502a

    Joined:
    Dec 30, 2008
    Location:
    Nottingham, UK
    #2
    In your MediaInfo report under video stream 1 there is a line that says:-
    Code:
    Video Stream BitRate Mode.........................VBR
    VBR means Varible Bit Rate, meaning the bitrate changes depending on the video complexity, for example really dark or black scenes will have a very low bitrate and really detailed scenes will have a very high bitrate. So the given bit rate figures are just averages. The same is true with the audio.
     
  3. AdrianK thread starter macrumors 68020

    Joined:
    Feb 19, 2011
    #3
    But if they're averages, it shouldn't matter, because you've already accounted for the fact that the bitrate fluctuates by averaging it...?
     
  4. roidy macrumors 6502a

    Joined:
    Dec 30, 2008
    Location:
    Nottingham, UK
    #4
    I see what your saying and to be honest I really don't know. The only way I can get them to add up is by counting each audio channel individually.

    Code:
    Video stream          -  3500
    Audio stream 1 Left   -  160
    Audio stream 1 Right  -  160
    Audio stream 2 Left   -  82.3
    Audio stream 2 Right  -  82.3
    Audio stream 3 Left   -  82.3
    Audio stream 3 Right  -  82.3
    
    Total                 - 4149.2
    Still not exact but a lot closer.
     
  5. AdrianK thread starter macrumors 68020

    Joined:
    Feb 19, 2011
    #5
    That's really interesting. Thanks for looking in to it :)
     

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