The best way to recompress ?

[Corrado]

Hi,

I converted some MiniDV tapes to DivX4. They look great on my PC (settings = 1236kbs, 496x400 pixel, Audio MP3 VBR 32-192kbs).

The problem is my father's PC, where video is jerky and audio goes out of sync because the processor is too slow (the video shows my son and grandpa' would eagerly have his copy... :) )

What should I expect recompressing the already compressed videos to lower resolution and lower bps? Could it be acceptable or should I reprocess everything from the start (re-capturing from MiniDV tapes, quite annoying, because I deleted the uncompressed AVIs... :( ).

Any experience done?

Corrado

[cordraconis]

I have some experience with recompressing (I had a AMD k6/-400, and no DVD player, so I re-encoded 2-CD-rips from a friend of mine).

I would recommend using the calculations from Gordian knot to have a good Bitrate/resolution ratio.

Then I would definately go for some filters. (Some kind of smoother or noise-remover is a must)
Also try a filter that removes some of the blocky-artefacts that era inherent to MPEG-compression.

Donald Graft's page is a good one for Filters.

I will try to find the URL and post it here.

About audio: a mono MP3-stream of about 64 bps is good, possibly even lower, but you'll have to try that first to hear if it sounds acceptable to you.
Dont go for a VBR-file, that is too much processor-load. (I never got things in sync, but on a Duron 800 it ran fine.)

If the bitrate you're aiming at is too low, than the processor has too much calc's to do, and it is actually worse than at a higher bitrate.
Too high bitrate and your system can have troubles also (maybe becouse of a limited bandwith ???)

Anyway, if you want to recompress, go for some filters to Clean up the pictures and to make them better encodable.

Good luck!

[cordraconis]

Here is the url, check it out.

http://sauron.mordor.net/dgraft/index.html


But before you try the (lenghtly) process of doing the video all over, first try to put a CBR-MP3-stream with the video.
(Demux with NanDub, recompress with LAME, reMux with NanDub)

I really think that 'll do the trick.

[Corrado]

Thanks twice :)
I'll try CBR then eventually smooth/resize/recompress

[trbarry]

Corrado -

Check first that he doesn't have a Matrox card or one of the other ones that needs a width multiple of 32 in order to use the video overlay properly. If that was the problem then there is a software fix for it.

- Tom

[Corrado]

Just to let you know the results:
I recompressed without filters (the source was a quite clean DV video and after some tests I decided to avoid filters) and the final videos are really nice, even a little sharper than the source.

Input: DivX4, 496x400px, 1236kbs (0.25 bits/px), VBR MP3 32-192bps
Output: DivX4, 400x320px, 750kbs (0.234 bits/px), CBR MP3 96bps
Video: VDub with D.Graft's Smart Resize filter (precise bicubic).
Audio: VDub with Radium MP3 codec.

I also made some test with other family movies that had problems on my father's PC:
Input: MPEG-1, 352x288px, 1500kbs, CBR MP2 256kbs 44.1KHz
Output: DivX4, 352x288px, 750kbs, CBR MP3 96kbs 44.1KHz
Video: VDub (fast recompress)
Audio: VDub with Radium MP3 codec.

ALso these tests were satisfactory, but sometimes, expecially during fast panning camera movements, I got noise in form of horizontal "lines" (2-3 lines, as wide as 20-30% of frame width, disturbing the image for about half a second). It shouldn't be an interlace problem because the source video was shot in progressive mode... I noticed those lines, although less evident, also in other DivX4 movies that I made in the past. Hints?

Corrado

[cordraconis]

Nope, no hints. (Well, not any helpfull ones :) )

I guess this is just a limitation of the "Lower Bitrate" of the movies.
(Especially because you told that it happens bith Fast movement-scenes.)

I think the best way of avoiding that, could be to give more bits to scenes with faster motion.
There is a tool for DivX 4 that could do that, but I have no experience whatsoever with it.

http://divx4log.narod.ru/

I got it from the thread "Trying to implement SBC for DivX 4", in the DivX4 Forum.

You can experiment a bit. (I am curious about it myself, but I can't try it right now.)

[obelix]

I have noticed similar line on a TFT of a notebook. These lines are there in fast motion scenes, but only if you pla fullscreen. When you watch the movie in a window, they are not there. On the notebook it is a speed issue, the video chip just in not fast enough. You also can get these lines with poor videodrivers, when I install Win2k on an Athlon1000, Asus A7V, Elsa Erazor3 (TNT2), Windows installs a default TNT2 driver. This one is nice for office use, but gives you these lines. I downloaded a new driver from Elsa, installed the latest VIA 4in1 driver and activated AGP Turbo. This helped, not one line is left.