Decompressing/recompressing an avi file

[n1koolkat]

I've twice downloaded a movie which on both occassions turned out to be corrupt. I've removed the bad frames by using virtual dub. It now says that there are now no frames however when played back in windows media player the movie cannot be fast forwarded and when it does, then video remain static or turns black but the audio moves forward. It fails to open at all when using DivX Player. Reindexing (whether with Virtualdub or DivFix) causes sync problems with the video and audio and does not resolve the problem when opened in media player or divx player. I tried to recompress the file and that resolved the problem however the quality of the video is now terrible. Is there any way i can recompress the file without a deterioration in quality or decompress the original video and audio and the recompress whilst still preserving the quality of the avi file.

I need to keep a copy of the avi file on CD before converting to mpeg to play back on a DVD player. Any help will be gratefully received. Thanks

[KingJohn]

Fast forward is a common problem with AVI's that don’t have many keyframes, but this does not mean they are no good. Having removed the junk frames, go straight to TMPGEnc and start the conversion. Stop after a few minuets to check the output.

Keyframes ever 300 etc are fine for playing from start to finish, and wont effect the conversion, keyframes every 10 are fine for editing and skipping through the video

[n1koolkat]

Thanks KingJohn. There were np problem converting the file to an mpeg format and the file worked fine, fast forward included. However I still want to keep a copy of the original avi form as backup. I've sometimes encountered problems when copying corrupt avi files from a CD to my hard drive (CRC errors) and therefore not been able to copy them. I don't particularly want to come across this problem and the mpeg file is too big for a single CD. I therefore need to make sure that the file is okay before copying it to a CD.

Again, I've also downloaded a avi file with audio sync problems which i want to correct before copying the avi file to a CD. I assume that this means following all the documents on audio synching. Does this not also mean that I have to recompress the file after I've corrected the synch problems. Which takes me back to the original problem. Is there anyway to recompress to a new avi file without losing the quality of the original?

[spidey]

if you get it suynched in Vdub you could frameserve directly to TMPG.

http://www.vcdhelp.com/virtualdubframeserve.htm

[n1koolkat]

:-? Apparently, I am a bit more of a newbie than I thought. Basically all I've done to date is experiment with converting from avi to mpeg to vcd. What exactly does frameserving do?

[KingJohn]

:Thanks KingJohn. There were np problem converting the file to an mpeg format and the file worked fine, fast forward included. However I still want to keep a copy of the original avi form as backup. I've sometimes encountered problems when copying corrupt avi files from a CD to my hard drive (CRC errors) and therefore not been able to copy them. I don't particularly want to come across this problem and the mpeg file is too big for a single CD. I therefore need to make sure that the file is okay before copying it to a CD.

Ok, well you proved it was OK by converting it to mpeg 1, there wont be any problems with copying it to a CDR, even if there were junk frames, the file structure is still correct and you should not experience any backup problems.

If you wanted to fix the keyframes, you would need to open it up in Vdub and select Video > full processing mode, then Video > codec > configure

From there you can chose a codec to match the original, and specify the same bitrate, but change they keying to "every 10"

Doing this will reduce the quality slightly, but if the source is a DVD rip, you probable not notice anything. If the audio is left on streaming, there should be a direct copy, but if the output has sync problems you may need to decompress it before re-compressing later lot of work involved, I would just store it as it is.

Again, I've also downloaded a AVI file with audio sync problems which i want to correct before copying the avi file to a CD. I assume that this means following all the documents on audio synching. Does this not also mean that I have to recompress the file after I've corrected the synch problems. Which takes me back to the original problem. Is there anyway to recompress to a new avi file without losing the quality of the original?

Sync problems during conversion can usually be cured by decompressing the audio and using it as a stand alone WAV

Audio > full processing mode
Audio > conversion > 44.1Khz
SAVE WAV

That can now be used in TMPGEnc with the original AVI, but make sure any AVI's you download are junk free, a few bad frames can mess up any conversion.

If the AVI has sync problems to start with, if you know how to fix them should you need to convert it again, it might be best just to back it up with the problems ?. Just as much work involved later that it would be now.

If you intend to share the program on Kazaa, then most people don’t bother to fix the problems, if you did and the file was then a lot smaller, it is no longer the same file that everyone else has got !!, multi downloads will accrue with all the other copies but not include yours. If you used sig2dat on a AVI you have fixed, you could see a new CRC code produced !

[n1koolkat]

:wink: Right, thanks, anyway I've decided to just experiment with the file and see if I can correct the audio sync problems and at the same time learn something more about encoding, compressing, conversion etc. What I would like to do is make the aspect ratio for the file slightly bigger. (It's currently 640x272). I'm trying to make it at least 640x288 before saving it as a new avi file. Could you recommend a programme that can do this. Virtualdub does not appear to have this facility and Tmpgenc appears to be for mpeg files only.

[spidey]

You may apply a RESIZE filter under VIDEO in VirtualDub, then Frameserve that into TMPG

[n1koolkat]

:( A resize filter? I've had a look in v1.4 of virtual dub and although I can see the Filters, I can see a resize option. Sorry to be a pain, but i'd appreciate it if you would 'splain to to me like a 10 year old or point me to where i can get further instrauctions. Thanks

[KingJohn]

Making the size bigger can result in the quality going out the window, However it can be done to the AVI or done when converted to mpeg 1. Usually using TMPGEnc to change things during conversion is preferred.

Vdub

Video > full processing mode
Video > Compression > codec > bitrate (needed for full processing mode)
Video > filter > Add > Resize


TMPGEnc

Load > VCD/SVCD Template
Load > Unlock Template

Setting > Video > size

Changing the size of the mpeg 1/2 to anything other than the correct size, may render the disk useless on your DVD