Colour Degredation Problems: HUFYUV->AVISYNTH->TMPGENC 2.51

[acanthis]

It's been a while since I've used TMPGenc for encoding as I've been converting most of my videos to Divx4. Just testing the latest TMPGenc (MPEG1 or MPEG2 encoding) with an AVISynth script I noticed very bad colour degredation in the output file. In fact, it looked as though the output had been dithered to 8 bit colour. Dreadful!

After much messing around, I discovered that if I recompressed the source AVI file the problem went away. I also discovered that I could fix the problem by making the last statement in the AVISynth script a ConvertToRGB (which should be unnecessary!)

This is new behaviour, which I had not seen in the older versions of TMPGenc I tried. I've used AVISynth scripts hundreds of times in the past with this encoder, using HUFYUV compressed source and had no problems.

The source file is 480x576@25fps captured with VirtualDub 4.8 using HUFYUV 2.1.1. The AVISynth script looks like this (for example):

AVISource("myfile.avi").trim(0,1500).bicubicresize (352,288)

Loading this into VirtualDub shows no colour corruption, but feeding it to TMPGenc results in an unwatchable file. I found that this can be fixed two ways ...

1) recompress myfile.avi with HUFYUV again.
2) add .ConvertToRGB on the end of the AVISynth script

Anyone else experienced this?

[acanthis]

... and of course I should have mentioned these versions:

TMPGenc v2.51
AVISynth v1.01

8)

[Dave B]

I remember that I experienced a similar thing whilst I was experimenting with capturing either HUFFYUV or MJPEG. I did a bit of research on the web and discovered that there was a bug or quirk in some YUY captures.

I changed the capture settings to 24bit RGB (greater CPU load ) and all was well

[Kdiddy]

There is a version 1.05 of avisynth out now. That may help.

Also, did you try increasing the priority of the directshow filter in TMPG. I havent used TMPG in awhile. But I think I remembered having this issue when last I did use it and this is what solved it. Also, from what Ive been reading as well, version 2.5 of TMPG is quite buggy. So I also would try versions 2.01 & previous.

[acanthis]

Thanks. I tried version 1.05 of AVISynth, but that had exactly the same problem. Worth a try, though.

I have to disable the DirectShow filter in TMPGenc to even open an AVSynth script.

[acanthis]

I remember that I experienced a similar thing whilst I was experimenting with capturing either HUFFYUV or MJPEG. I did a bit of research on the web and discovered that there was a bug or quirk in some YUY captures.

I changed the capture settings to 24bit RGB (greater CPU load ) and all was well

I think this is where the problem lies. VirtualDub, incidentally, quite happily handles the files with no sign of colour degredation, which is why I hadn't noticed this until now - I'd been using VirtualDub to crop and filter then do a two pass compress with DivX.

I'll try changing the capture settings to RGB. As you say that will mean a significantly increased CPU load; at 480x576 I doubt my pathetic Athlon 1GHZ with its 60GB 7200RPM UDMA/133 disk will be able to keep up!

From further tests, I have confirmed that the workaround is definitely to add a ConvertToRGB at the end of the script - so I can workaround it - but these things just niggle me

Thanks for your help.

[Kdiddy]

No I mean, take your "ConvertToRGB" line out of your avisynth as well as any Audio references. Then increase your directshow filter.

[McQuaid]

I have this 8 bit colour problem as well. Have you found a solution yet. I'll post here what I find.