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  1. #1

    Member Since
    Aug 25, 2008
    Movie data Rates
    I've recently made some quicktime movies using H.264. The data rates are in the range of 6000 kbits/s according to the Quicktime inspector. I have a book on iMovie by Pogue that says data rates should be around 20k/second for cable modems to 250K/sec for hard drives. The 6000 kbits/s runs nice and smooth which doesnt make sense if the max should be 250.

    Does anyone have some guidelines for data rates?

    Is it possible that the book's K is Kbytes and not bits?


  2. #2

    xstep's Avatar
    Member Since
    Jun 25, 2005
    On the road
    2011 MBP, i7, 16GB RAM, MBP 2.16Ghz Core Duo, 2GB ram, Dual 867Mhz MDD, 1.75GB ram, ATI 9800 Pro vid
    I haven't seen the book, but I'd guess it is talking KiloBytes and the abbreviation should have been KB, not simply K, because K simply means 1024 (or 1000 depending on context) and you need a second letter to indicate what the measured quantity is.

    20KB is 20*1024*8=163,840 bits which is far short of what a cable modem can handle on a download, but higher than many DSL connections. I think my cable is capable of 5 mbit/s down. Of course that isn't consistent, and far short the 100mbits/s of the ethernet cable you likely have connected to such a modem.

    250KB/sec is about 2,048,000 bits/sec, only 20% of what a DVD player can handle. 6000kbits/s is about 60% of the 10mbit/sec that a DVD player can handle.

    My latest video which I placed up on a family web page is 1042.7 kbits/s, or 1.04 Mbits/s. The file is 10.3MB for a 1 minute 23 second video at 640x480 resolution. It is clear and that size is the native size as taken from my built in iSight. A similar experimental video from my iSight is 38MB, just under 20 seconds, 640x480, using the Apple Intermediate Codec (AIC) and the data rate is set at 16.31Mbits/s.

    I listed all of the above to show that a definitive answer isn't in a book regardless of your understanding of bytes and bits in the book.

    Your overall settings for a video comes down to compromises. The family video is small enough so that viewer can start watching it while to rest of the content downloads. As long as they have a speedy internet connection, the movie will not suddenly stop due to lack of loading the content. A 1.5 Mbit/s DSL line will do. If I was placing the family movie onto a DVD as a QuickTime movie, I would have picked a much higher rate. Same if the intent a playable DVD because I know iDVD will re-compress it to MPEG-2 and I'd want that compression routine to receive the best quality I could give it.

    Knowing your distribution medium and your audiences capabilities can help you decide on your export settings. Much of it is personal taste, but sometimes your goal includes fitting into some remote parameter that you don't control, such as an upload file size limit.
    CameraTime - Time lapse photography for novice and advanced users.

    When asking questions, post the version of your software. You'll receive better answers.

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