1 Reply Latest reply: Jul 27, 2010 6:41 AM by Jeremy Hansen
rocklebee Level 1 Level 1 (10 points)
Hi i'm a user of pro video apps and i have a question that i'm having trouble finding answers to.

I'm trying to decipher all the different ways data rate or bit rate is reported in different info screens in OSX.

Case study:

exported an mpeg 4 of a 2 minute video i edited. was told by web designer the specs and followed exactly. Used the MPEG 4 preset in FCP>export using quicktime conversion. vid size was 480x360 bit rate was set to 500, and honestly i don't remember what the audio settings were.

video came out to 30 megs which seemed a little high to me. and the web designer suggested i lower the bit rate to get the files size down bc when he viewd the info in QT it said it was around 1500.

now here's my confusion. I encoded the vid at 500kbps. QT7 reports the "data rate" as 1687.21 kbps, putting the vid in iTunes the info is "bit rate" 101 kbps and "total bit rate" 1685, opening info from Finder, "total bit rate" is 604. what is one supposed to make of this info.

i realize that total bit rate includes the audio as a sum of the video and audio rates. and i realize that it's reported as an average with VBR formats, but why the differing "total bit rates" btw Finder and QT? where does itunes get the 101 kbps from. does this mean that even though the vid was encoded at 500 kbps that the audo rate was around 1000 kbps?

any info greatly appreciated.

MacBook Pr0 2.33 intel, Mac OS X (10.6.4)
  • 1. Re: Confusion about bit rates and total bit rates
    Jeremy Hansen Level 4 Level 4 (1,900 points)

    exported an mpeg 4 of a 2 minute video i edited. was told by web designer the specs and followed exactly. Used the MPEG 4 preset in FCP>export using quicktime conversion. vid size was 480x360 bit rate was set to 500, and honestly i don't remember what the audio settings were.

    video came out to 30 megs which seemed a little high to me.


    That's not right. 500kbps * 120 seconds / 8(bits in a byte) = 7500KB

    now here's my confusion. I encoded the vid at 500kbps. QT7 reports the "data rate" as 1687.21 kbps, putting the vid in iTunes the info is "bit rate" 101 kbps and "total bit rate" 1685, opening info from Finder, "total bit rate" is 604. what is one supposed to make of this info.


    That is closer; 1685kbps would come out to around 25MB.

    You used the mpeg4 export, right?

    It looks to me like something went wrong (computer or user error) with the export. It is possible that you somehow circumvented the bitrate setting. Perhaps you entered a bitrate in the box, and then clicked automatic?

    I have no idea about the Finder bitrate. I've seen some pretty weird numbers there. But the others should square up more or less. I don't think your export went as you intended.