Divx and file size

[perdomot]

I was under the impression that when you used the divx codec to encode an avi file, you could create files that were even smaller than mpeg files but of at least equal quality. Is this correct and if so, what is the bit rate I should choose? My goal is to have files that are smaller than mpegs but of equivelent quality. Thanks.

[DJRumpy]

DivX is a variant of MPEG-4. You should use a bitrate of at least 800 kbps for higher resolution pics. Expect DVD quality to take about 1-2 GB. If you go into the lower kbps ranges 600-700, you can easily squeeze them into 700-1GB range.

[Gazorgan]

You should be able to get a 'DVD Quality' movie onto 2 CDR's. You can't really do it on 1 CDR, not without lowering the resolution and dropping the audio to 2 channel. 640x272 is close enough to 720x480 letterboxed that I can't tell the difference on my computer. Only by looking at backgrounds in slow scenes can I tell the difference.

This is working from the original DVD. Working from MPEG's (SVCD) is a different kettle of fish. You are trying to encode something with flaws (noiese/macroblocks), so you are going to lose some bitrate to that....but you can still convert it to a 2 CDR movie.

If you want VCD resolution you can hit a 1 CDR movie.

[perdomot]

Well, I've been experimenting with both 600 and 800 bitrates and the amount of pixelation is high at those rates and the file size is bigger than mpeg. Am I doing something wrong? I thought the divx codec could produce higher quality files at the same file size or maybe even smaller. Was I wrong about this?

[DJRumpy]

Which codec are you using? Also, what motion detection settings? You can always do multi-pass to reduce the pixelation, or eliminate it completely. I never use DivX, but I get excellent results with XviD (another MPEG-4 codec). I agree with Gazorgan. Most of the higher quality DivX files you download off the net will be 640 horizontal. The file size should be smaller than MPEG-2.

[perdomot]

I've got the 5.02 codec. The newer ones don't have as high a bitrate as the 5.02 version.

[DJRumpy]

I'm using 5.03 for that particular codec, and it goes to 4000 kbps, which is far more than any DivX video should ever need. Do not confuse this with the kbps that you use with MPEG-2. An SVCD using CBR can use about 2778 kbps. An XviD/DivX file can do the same thing with 700-800 kbps. Make sure your encoding bitrate is set to 700-800 give or take. Use a bitrate calculator to figure out what you need (Find the FitCD tool in the TOOLS section. It has a DivX bitrate calculator). You should also do 2-Pass, rather than a single pass. Your macroblocking problem on scene fades/changes will disappear and your overall quality will improve. If your not sure how to do this, just post, and I'll see if I can walk you through it.

[Gazorgan]

I have some DivX with upper bitrate of 2000 and average bitrate of 800 that are truly DVD quality. Since I'm handy with VDUB, I don't use some of the DivX Pro built in functions, but it can do a pretty dam good job. The biggest problem people have is they don't have a clue what the first pass is supposed to do, and how it's different form the second pass(do you know?). XviD deals with this nicely, and DivX doesn't.

I personally like XviD, since it takes the extra step and hits the file size for me instead of making me calcualte it (well, I gotta subtract the audio). Best part about XviD, is after the first pass...I can tweak settings until the 2nd pass looks awesome. It retains the first pass stats in a file forever if I need it.

[SaSi]

Allow me a comment regarding bitrate selection and DivX. Choosing any bitrate generates a Constant Bitrate video stream, with all the drawbacks of CBR. Almost nobody is encoding MPEG-2 in CBR for these reasons: High motion scens will lose quality and low motion ones will waste it.

I have always used DivX with Constant Quality encoding. For temporary conversions, I would use a CQ of 2, the best quality. Such encodes would always produce files smaller than the equivalent MPEG stream. For final encodings, for DVD material, a Q=2.6~2.8 is fine and further reduces the file size.

Another point. Don't forget to compress the audio as well. And use Constant Bitrate at 128kbps, preferably an MP3 codec. You can also use 64kbps joint stereo if you want as well; quality is not totaly lost.

In average, I dare say that DivX can compress video at almost 1/3 the size of MPEG-2 for similar quality. Except some special cases, like Armagedon, which has so much action that it cannot compress that good.

[DJRumpy]

I do like the size function in XviD (I don't use DivX). The only problem with XviD, is you don't have a choice. I often like to encode a small clip to view the results. Not easy, when your trying to specify an output size. It's great for putting an XviD on CD. Not so great for small clips if you want to use multipass. I wish they would fix that to give you a choice of output size, or bitrate. Perhaps they already have. I don't convert TO DivX/XviD much. I convert FROM them on a regular basis.

The 2-Pass methods used by both are somewhat more manual than the MPEG-1/2 encoder methods. You should not change your compressability settings though from pass to pass. They should remain consistant for each pass. If your changing them, and getting good results, then your just getting lucky. Even the docs will tell you this. The other down side is that you have to manually start each pass (I'm guessing there is some sort of auto-batch tool though..there always is).

In either case, until/if DivX capable players become common place, both of these will remain something that I usually convert from, and not to