Optimizing AVI's for playback from CD-ROM

The size of the avi file is not really important. The real issues are the speed (data transfer rate) of the CD ROM drive & the optimal data rate of the compressed clip. To get smooth playback, you need to get the data rate of your clip down to a level that the CD drive can handle. A 2x drive is rated at 300 Kb/sec & a 4x drive 600 Kb/sec. However, drives are often rated optimistically & the actual transfer rate can be somewhat less depending on a number of factors. A good target to aim for is 240 Kb/sec as this gives a safety margin on even the slowest drives.

First up, you will not get satisfactory playback if you captured *and* compressed the video in real time. The clip may run OK off the HDD but off a CD drive it will jerk all over the place.

This is the way we do it:

  1. Capture the video in Indeo RAW format, or better still use the Indeo YVU9C codec. This is available for download from the Indeo site. It does a minimal amount of compression on the fly with virtually no loss of quality & the captured file size will be about 40% less than the RAW format. On a Pentium 90 with a reasonably fast HDD you should be able to capture 320 x 240 with audio without any dropped frames.
  2. Do your off line editing in DVP, Premiere or whatever. *Do not* do any compression or re-compression during the editing process unless you have compelling reasons to do so.

    Now you come to the important bit. For avi you have a choice of 3 codecs:
    1. Microsoft 1: 8 bit or 16 bit. For standard video this is not a good choice. It is better suited for animations such as flc & fli *as long as they don't have any color gradients*.
    2. Indeo 3.2: A good choice. It will play back smoothly from a VL BUS 486 with a 2x drive. It is a 24 bit codec but does a reasonable job of rendering down to 8 bit on graphics adaptors set to 256 colors. Video quality at 16 bit or higher settings is excellent.
    3. Indeo ivi (4.*): The best choice. This is an excellent 24 bit codec & playback quality is close to MPEG but.... unless you know that your end user has a Pentium 166 or higher, forget it. Being a highly efficient codec, it require a lot of CPU power to decompress & get all the pixels on the screen in real time.

    In my humble opinion, Indeo 3.2 is still the safest & best choice for general consumption at this time.

  3. From DVP or whatever editing program you are using, set up your offline compression parameters as follows:
    1. select your codec (Indeo 3.2 or whatever)
    2. Set your output video format (320 x 240 or whatever)
    3. Set your audio options
    4. Set the frame rate to 15 fps
    5. Check the "synchronise video" option
    6. Ignore the bit depth option. Indeo 3.2 & 4.* default to 24 bit
    7. Set the data rate to 240 Kb/sec (this is critical)
    8. Set key frames to 4
    9. Set quality slider to 100%
    10. Check "pad output for CD ROM playback" to on (This is critical for slow CD drives)
Now hit the button & compress the video. It will take a while. Example, a compressed avi file with a finished size of around 100MB will take 30 to 40 minutes depending on your platform & your editing program. DVP 4 (32 bit) is faster than DVP 3 (16 bit).

Note: you can play around with the data rate but below 240 Kb/sec quality will deteriorate rapidly. Above 240 kb/sec doesn't give any noticeable improvement in quality, at least I can't see it. 240 kb/sec is generally accepted as being the sweet spot.

That is the procedure we follow. Some of our video files are very large. 320 x240 with narration, 150MB + & 7 to 10 minutes duration. They play back smoothly from a properly set up 2x drive & are no problem at all on a 4x drive.

Hope this helps.

Geoff Pearson
iqtech@WAVE.CO.NZ
I.Q. Technology Ltd.