Mpeg2 looks better than Divx after transcoding to DVD?

[perdomot]

I decided to do a little testing on image quality and noticed that when I used Nero to author my own DVD, the mpeg2 file looked better than the Divx. I thought that since Divx was a higher resolution codec, it would look better but there were definately more blockiness and artifacts in the Divx after the two files were transcoded and burned to dvd by nero. Any idea why? The file specifics for both formats were:

352 X 240
2200 birate
encoded from an avi file from a VHS tape

[jimmalenko]

So .... what did you do again ?


As I read it, you converted an AVI file of a VHS tape to Divx, then ran that through Nero to create a 352 x 240 @ 2200kbps DVD. Then you converted that same AVI file to MPEG-2, then ran that through Nero to create a DVD.

How am I going so far ?



BTW, completely blind here, but I wouldn't mind betting that the "cause" is Nero transcoding.

[perdomot]

You are correct, that's what I did. I do know that the transcoding process is going to lower the image quality but what I can't figure out is why the Divx file looks worse than the mpeg2 file after nero transcodes it. I thought the Divx file would provide a more detailed image for nero and thus produce a better looking image after the transcoding but its just the opposite. Any ideas why that is?

[Abond]

I think this is because the divx route is transcoded 2 times:
Captured avi --[lose quality]-->DivX --[lose quality]-->Mpeg2
And the mpeg2 route:
Captured avi --[lose quality]--> mpeg2 . At this point Nero didn't re-encode the file.

I thought the Divx file would provide a more detailed image

If you think "more detailed image than the original avi" you are completely wrong. It is in opposite - less detailed image.

[Nelson37]

Why is it that you call Divx a "higher resolution codec"? A 352x240 file is a 352x240 file, whether uncompressed or WMV.

Divx is a hi-Compression, processor-intensive codec intended for PC playback. It is also not totally standard, possible a prog could decode with MPG4 or something else, or just not handle it properly. You are not testing how good Divx looks, but how well Nero happens to handle it.

For a real test, decode both source files to uncompressed AVI and re-encode that.

Best would be to encode, from original source, one-time-only, to target format, using best available software.