How do you ensure your DVD backups to .avi don't lose too much quality?

[b0mbrman]

I travel quite a bit so I encode my DVDs into .avi files in order to minimize what I carry. After some trial and error and playing with the variables, I've found that the number that matters--assuming sound quality and other factors equal and that videos are watched at full screen--is:

bitrate adjusted for the effective resolution

...where the effective resolution is the resolution of the video adjusted for the resolution of the monitor you'll be playing. The adjustment is the fraction of the full screen your video will be using.

You can find this number through the formula:

Sv / Tv x e^(-ABS(ln((Wm/Hm)/(Wv/Hv))))

...where the variables are:

Sv = File size of video
Tv = Time of video
Wm = Width of monitor
Hm = Height of monitor
Wv = Width of video
Hv = Height of video

My target value for this equation is 10...

 

[Munky]

Where does bitrate fit into that equation? I use a somewhat different formula, and it basically relies on bits per pixel per frame to measure video quality. You'd want to keep that number greater than or equal to .2

 

[b0mbrman]

Originally posted by: munky
Where does bitrate fit into that equation? I use a somewhat different formula, and it basically relies on bits per pixel per frame to measure video quality. You'd want to keep that number greater than or equal to .2

It's a bitrate...just in units of MB/min rather than bps...or am I using the term wrong?

Now, with your way, wouldn't you want more bits/pixel for a smaller resolution video (assuming your watching your movies on a monitor of constant size at full-screen)?For example, if you have a 320x240 video, wouldn't you want double the bits per pixel of a 640x480 video?

Also, if a video has an aspect ratio so that there's a lot of black at the top and bottom of the screen, wouldn't a lower bitrate be allowable?

 

[Noema]

Pardon my ignorance, but how can one encode the .vob files from a decrypted DVD into .avi?

 

[b0mbrman]

Originally posted by: Noema
Pardon my ignorance, but how can one encode the .vob files from a decrypted DVD into .avi?

More than a few ways: SUPER, videora, AutoGK, virtualDubMod to name a few. I use AutoGK.

 

[Fallengod]

Well most people dont make backups of dvds into avi files heh.

 

[Noema]

Thanks b0mbrman!

Originally posted by: modempower
Well most people dont make backups of dvds into avi files heh.

Heh, indeed, I suppose there's a loss in quality. But I'm in a similar situation in which I sometimes travel and it would be nice to have them in my HDD, but the 4GB files one gets after merely decrypting the DVD with DVDshrink are somewhat...unwieldly

 

[b0mbrman]

Originally posted by: modempower
Well most people dont make backups of dvds into avi files heh.

Well, yeah...I guess technically they're not "backups." Just ways to make them more portable...

 

[Munky]

Originally posted by: b0mbrman

Originally posted by: munky
Where does bitrate fit into that equation? I use a somewhat different formula, and it basically relies on bits per pixel per frame to measure video quality. You'd want to keep that number greater than or equal to .2

It's a bitrate...just in units of MB/min rather than bps...or am I using the term wrong?

Now, with your way, wouldn't you want more bits/pixel for a smaller resolution video (assuming your watching your movies on a monitor of constant size at full-screen)?For example, if you have a 320x240 video, wouldn't you want double the bits per pixel of a 640x480 video?

Also, if a video has an aspect ratio so that there's a lot of black at the top and bottom of the screen, wouldn't a lower bitrate be allowable?

For lower resolution video I use lower bitrate to keep the file size down. Bitrate will not make up for the details lost to the lower resolution. On the other hand, increasing the output video resolution while keeping a constant bitrate will increase compression artifacts, since you now have less bits to cover a certain area of pixels. So, in general a higher resolution also requires a higher bitrate. As for black bars on the top and bottom of screen, I always crop those out in the encoded video.

 

[gsellis]

The whole problem with this thread is, what codec? AVI is just a container. If you put a 1.5hr movie into DV-AVI, it would be about 22GB. If you converted it to DivX or WMV, it could be 2GB.