Help reencoding AVI

[Eyael]

Hi!

I have a couple of AVI's encoded with XVID with GMC option. Apparently my standalone DVD player (Philips DVP 5500) cannot read them even after I've removed Packed Bitstream (using Moitah's MPEG4 Modifier). I guess the only solution is to reencode the AVI's.

So my question is : since I no longer have the captured sources (only the XviD-AVI's), can I just re-encode the AVI's with same resolution, bitrate, etc., without the GMC option (I always use GordianKnot to do my encodings)? Or would it be best to re-encode using DivX and activate the GMC (since all my DIVX-AVI's with GMC work perfectly on my standalone) to ensure equal quality? Or is there another way?

Thanks for advising me.

[manono]

Hi-

Either way should work; XviD with no GMC or DivX with GMC. One easy way to get the job done is to use AutoGK. Install it with the ESS chipset option, to insure standalone compatability, and set it up for the same video filesize and resolution and wait a bit. If you have several AVIs to convert, you can set them all up once, and then use the batch feature to encode them one after the other,.

[Eyael]

Thanks for replying so quickly.

I have tested on a short clip and even though I get better quality with XVID without GMC than DIVX 5.2 with GMC, I still have quality loss (I have done a two pass encoding). I guess it is because I have removed the GMC (3 warp points).

Is there a way I can improve the quality without increasing the file size too much (to fit on a CD)? I could cut the end credits which I usually encode with poor quality. Would increasing the bitrate do the trick? I have no QPel and no adaptive quantization (I'm talking about XVID 1.1.0)

[manono]

Hi-

You'll always get quality loss. You're reencoding to a lossy format (MPEG-4). So, it was originally encoded lossy, and now you're reencoding to a lossy format. The quality degradation is compounded. But you tested on a short clip, so I don't know if you used the same bitrate as the original. You can find the bitrate the original used by opening it in GSpot. But, that will be the bitrate for the entire movie, and not the scene you picked to test, which may have had a higher (or lower) bitrate originally.

You won't be able to improve the video quality, no matter what file size you give it. About all you can do is to keep from degrading it any further than necessary. Your best bet would be to run a 1-pass with a fixed quant, 2 for best quality (and largest file size), 3 for slightly lesser (but maybe unnoticeable) quality. So, you can try a Single Pass with a Target Quantizer of your choice.

[BigDid]

... Is there a way I can improve the quality without increasing the file size too much (to fit on a CD)? ...
Hi,

I have nothing to remove from manono's post :)

The only thing is (as quoted) if your max size is 1cd=700Mb, that could be way too small size for a fixed 2 or 3 quant; you can ask AGK to make a 2 pass with that size and it will try to keep the less bad resolution for that source and that size.

Why less bad? because if your source avi is less than 700mb, it will be a low bitrate (guess 700 to 900kbp/s,) not so sharp and already without fine details, so the re-encoding cannot be good (see Manono's post about lossy codec).

You don't state if you usually use programs like VDubMod or others that can manual encode or if you just begin with AGK or similar all in one?

If AGK only, raise the size for a 2pass encode and compare the avi's made by the comptest (+- 10mn each time, abort just after) until it fit your needs.
IF VDM or others, well you know the how-to and the possible avisynth filters improvements :)

Let us know if any success.

Did

[Eyael]

Thank you both for your helpful advice.

To answer Manolo's question, when I mentioned a short clip I meant a trailer so I made a test on the full avi. The bitrate used was the same.

I do not use Auto GordianKnot but GordianKnot and the video encoding is made with VirtualDubMod using AviSynth scripts I imagine (I never use extra filters and usually keep the selected resize filter which is most always Lanzcos but here no resize needs to be done).

I was wondering whether converting the AVI to DVD and then back to AVI would change a thing?

[BigDid]

Thank you both for your helpful advice...
You are welcome.

...I was wondering whether converting the AVI to DVD and then back to AVI would change a thing?
Yes:
MEPG2=lossy
MPEg4=lossy
lossy+lossy=2 x lossy :D

Did

[Eyael]

Ok, I guess that's pretty clear ! ;)

[BigDid]

One or two tips.

-The Philips 5500 has a MTK 1389 chipset so you can use custom CQM( matrixes) like Sharktooth ULR3, quite sharp for low bitrates or V2/LR quite good and sharp for medium bitrates.

- Concerning the filtering you may, I repeat may, have some improvements using very effective denoiser like Frfun (soulhunter) or Fft3dfilter (Fizick) and sharpener simple and effective: removegrain(mode=25) or the actual reference: Limitedsharpen (Didée) it's a script, not a plugin. Use search for all these.

Did

[Eyael]

Thanks for the tips. So I need to use the custom matrix instead of the usual H.263. Is that correct?
I found the ULR3 but I cannot find the other, the V2/LR. A link would be welcome...

By the way what is considered as low, medium or high bitrate?

I've read in a DivX encoding manual that a low bitrate is below 700, medium between 700-1000 and high above 1000.

I have some avi's on 2 CD's with bitrates around 1200-1350, can I call them "high bitrates"?

[Blue_MiSfit]

That's what DivX says... The general consensus around here (since most people are doing DVD backups of movies onto CD-R or fractions of a DVD-R) is that:
700-900kbit/s = lower bitrate (1cd usually)
1000-1500kbit/s = medium bitrate (1/4 dvd or 2cd)
above 1500kbit = high bitrate (2cd or 1/2 dvd)

If you want to preserve the best quality from your GMC encoded XviDs... you could just re-encode them to DVD. This gives you tons of bitrate, so you wouldnt loose too much quality... BUT, always remember the mantra of the video encoder - garbage in, garbage out :)

I think going from xvid_gmc->dvd might give better quality than xvid_gmc->xvid

[Eyael]

Thanks for the precision. Unfortunately I only have a CD burner. I might try and do a 2 CD for the AVI's on 1 CD. For those on 2 CD, the bitrate will be higher so hopefully the loss will be less noticeable.

[BigDid]

Thanks for the tips. So I need to use the custom matrix instead of the usual H.263. Is that correct?
I found the ULR3 but I cannot find the other, the V2/LR. A link would be welcome...
Here: http://forum.doom9.org/showthread.php?t=83125
The ULR, LR (and others) are listed not the V2, but all his CQM can be downloaded from Sharktooth signature

By the way what is considered as low, medium or high bitrate?
Same link as above or here: http://forum.doom9.org/showthread.php?p=796900#post796900
The whole thread is interesting :)

I have some avi's on 2 CD's with bitrates around 1200-1350, can I call them "high bitrates"?
I would call it medium (for xvid), somebody else would call it differently, this is a neverending discussion :D
All this also applies for DVD/Capture to avi encoding/conversion.

Did

[Eyael]

I have done a test with the same clip using Sharktooth's v3ulr_rev3 with two passes and I've noticed a little improvement. I have also set VHQ for I-Frames and VHQ=4. I was surprised it didn't take more time encoding (the clip is less than 5 mn still I expected it would double time or something). How can it be? To re-encode a whole movie already encoded with XviD, is it really worth selecting the maximum for VHQ and what's the use of VHQ for I-Frame (I've read in a post someone advising it but he didn't say why)?