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Getting larger files than expected using Xvid to compress AVI

This discussion thread has 4 messages.

#1
Hi all, I am having a problem and was hoping someone might be able to help me out.

Using Virtualdub, I have ripped an old, 90-minute interlaced VHS movie to uncompressed AVI. The file is 144 GB in size. I want to be able to reduce the size to a compressed AVI format that is under 1 GB but still retains the original video quality.

Using Virtualdub as my editor, I have used the XVid codec and its included Minicalc program to find a bitrate that will provide results for under 1 GB in size, but test runs always produce very noticeable artifacts. To retain similar quality to the original, the smallest file I have been able to create is about 4.7 GB in size. I suspect it can be made smaller, though, because I have seen 2-hr DVD movies in HD that were encoded with XVid that were under 1 GB in AVI format, and these movies retain a high level of their original quality. What is the trick that these ripped DVDs are using to get such good compression/quality ratios? When I look at the DVDs' file information in Virtualdub, they have unfamiliar framerates such as 23.97 or 25, whereas the VHS movie I ripped has 29.97. I am afraid to tinker with the framerate as I understand it could de-synch my audio. I also notice that the DVD rips have odd resolutions such as 624x272, 720x304, 608x256 and the like. My rip is standard 4:3, 640x480. Do I need to drop my framerate or adjust my resolutions? I can't imagine that this should be necessary. I suspect I am missing something else.

Thanks,

-Paul
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#2
The size of any compressed file will always be the product of the running time and the bitrate (time in seconds x rate).
Neither the resolution (frame size) nor frame rate affects the size of the output.
(North America) NTSC video (for playback on a TV) is 29.97fps.

Newer compression methods (with smaller file size) generally give better results than the older codecs like XviD (.mp4 using x264 codec?) but the quality can't be better than the original and playback on a standalone DVD player is out.


I would try the Videohelp forum for more expert advice.

http://forum.videohelp.com/forums/10-Capturing
#3
Thank you. If you don't mind, I will repost my question (with your reply) to the other forum, to see what others have to say.

Good to know about the bitrate * seconds rule. That makes sense. Still, some of the DVD rips were encoded in XVid and they seem to be a LOT better quality than what I was able to get from the tape. I wonder if that had anything to do with my source being from VHS and interlaced. The uncompressed tape rip, on the other hand, was true to the quality of the tape, which was also pretty good.

I have no idea how some of these DVD rips got down to bitrates of 112 kb/s while still preserving so much quality.

-Paul
This message has been edited since its posting. Latest edit was made on 18 Aug 2011 @ 2:27
#4
Hi attar, this question was resolved by the experts at VideoHelp. The thread can be found here:

http://forum.videohelp.com/threads/3380...895#post2103895

Thanks for responding to my question and pointing me in the right direction.
This message has been edited since its posting. Latest edit was made on 03 Sep 2011 @ 3:44
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