Questions about "data rate" when encoding files with DivX 5 for CD playback

[Morgulvale]

Hello.
The general drift of the question is this: is there some limiting "data rate" that the divx file should end up having after encoding to ensure the CD or DVD drive will be capable of playback without stuttering? And if so, is there a good way to handle the tradeoff in picture quality?

Now here's the specifics:

I'm trying to take some of the video I shot with my Sony miniDV camcorder, encode it in Divx, and put it on a CD-R for sharing with other family members. I transferred and edited the video using Pinnacle Studio 7 and then output to an AVI file using the miroDV2AVI codec (this was Studio's default setting for "keeping the properties the same as the original footage" and I think the same codec was used in getting the video of the tape in the first place).
Anyway, I ended up with a 3.19Gb file with these properties (according to Windows XP):

image: 720x480
audio: Duration - 0:15:20
Bit Rate - 1024kbps
Sample size - 16bit
format - PCM
video: Frame rate - 29fps
sample size - 24bit
compression - miroDV2avi

I then began using Virtualdub several times to try to come up with a DivX file that my DVD drive could handle playing back without stuttering. Generally, I've been using a resize filter to knock the image down to 320x240 along with 2 passes of the Divx 5.02 pro codec and encoding the audio as a 96kbs mp3.

All other options being held constant, it seems that I have to keep reducing the bitrate in the Divx5 config to end up with a file that has a "data rate" (I thought these were the same thing) low enough for good playback on a CD-R. The problem is that lowering the bitrate like this seriously degrades the picture quality of the original file.

In the past, I've encoded a few DVDs of a television series using Gordian Knot with a selected bitrate around 800kbps. This resulted in Divx files that windows says have a data rate of about 125kbps and these files play just fine off a CD. The difference is, the ripped and encoded shows come out looking fine with this lower data rate, whereas my video does not.

Any help or advice would be sincerely appreciated. Oh, incidentally, I believe I do have DMA turned on already.

Thanks,
Morg

[khp]

First of all the bitrate may vary wildly durring a clip depending on the amount of motion in the scene. The info displayed by windows is rather meaningless.

But under normal conditions, a resonably fast computer should have no problems playing CD encoded at an average of 2000kbps or above (assuming that you can play it OK from HD).
I would suspect that you either haven't got DMA enabled on your cd drive, or you got some serious quality issues with your buring process.
Check the IDE controllers properties page in the DeviceManager to check if DMA is enabled. How fast can you copy a burned CD, from CD to HD ?.

To improve the quality of your DV caps you might want to play with some noise filters.

[Morgulvale]

Hey, thanks for the fast reply.

Yes, originally I figured it must be a DMA problem. I recently upgraded my mobo and cpu and decided to switch to Windows XP. When I first tried to go into the device manager and make sure DMA was enabled I couldn't find the checkbox in either the DVD tab or the IDE controller tabs. I thought this was strange since windows help kept saying it should be there, but I could never find it. So, after digging around a bit online, I found an article on the windows support site that said DMA is automatically enabled on all DVD and CD-rw devices. So, I took this at face value which may have been a mistake, but since I have no option to manually enable DMA, I didn't see what choice I had.

I've tried two different burning programs and both seemed to do just fine, but you're right....The files play fine on my HD, yet when I did an experiment to see how long it would take to move the file from the CD to the HD, I was horrified at the amount of time it did take.

The DV looks fine after the initial capture. It's after I scale it down and compress it that I start to see the artifacts. I will try a noise filter, though. Thanks for the suggestion.

[khp]

Originally posted by Morgulvale

When I first tried to go into the device manager and make sure DMA was enabled I couldn't find the checkbox in either the DVD tab or the IDE controller tabs.

It is in the IDE controllers properties page under the advanced settings tab.

Originally posted by Morgulvale

So, after digging around a bit online, I found an article on the windows support site that said DMA is automatically enabled on all DVD and CD-rw devices.

I wouldn't trust this even if BillG told me so.

Originally posted by Morgulvale

The DV looks fine after the initial capture. It's after I scale it down and compress it that I start to see the artifacts. I will try a noise filter, though. Thanks for the suggestion.

Yeah, The size reduction in itself should reduce noise quite abit. But a temporal smoother/cleaner might be of some use. But I'll admit that I have no experience with DV captures so I dunno.