Quality vs. Size

[Shadowmistress]

Since I've started surfing this site a couple of years ago I've done ALOT of reading and ALOT of testing on my own. What I notice on these boards is that people become "specialists" on some qualities more than others. It is exactly that expertise I'm trying to pool together to get a converting formula even a total newbie can understand (so keep the language simple folks).

Objective: To get the smallest MPEG-1 video filesize possible without seeing all those "boxes" on the screen.

Intension: #1. To burn multiple files to a non-standard vcd which I can play on my dvd player. #2. To store permenantly on my limited spaced harddrive.

Sources: Avi's of various sizes, biterates, codecs, ...you name it.

Tools: Tmpgenc 2.5 (freeware), Nero 5.

Target Quality: The same as a VHS video cassette taped using Extra Long Play setting (only slightly blurry).

For the sake of arguement lets say we are working with "X.avi" which is:
352x240
29.97 fps
120 minutes
700 mb

*After* you've reduced the biterate to as low as you can stand to get the quality you like, how can you reduce the filesize further?
(If you are encoding audio with tmpgenc also, make sure to set the audio biterate to the lowest setting.)

Here is what my personal tests have found so far:

Don't use "soften block noise": it actually makes the file slightly bigger and you get a pulsing effect when you watch the movie (like someone has their finger on a blur button and they keep pressing it once a second while the movie struggles to go back to its original setting.)

Sacrifice brightness: although I'm still researching this, apparently the lower you bring down the brightness and contrast and color saturation, the less bytes it takes to encode the frame. Bright movies (lots of daylight) will be bigger than dark movies (lots of shadows) even though they have equal time and framesize. Personally I don't like messing with these settings but we're talking about what's possible here.

Sacrifice size: If you make the picture smaller than 352x240 to either 256x176 or 176x120, you can burn to a disc and use your DVD's zoom feature to bring the picture up to size on the tv. If the picture size is 50% of its original the filesize will be 50% of it's original, not accounting for audio size. Remember that it will get blurrier the smaller you go and you will lose resolution.
Tip: best way to do this is to encode a still picture of a letter with a series of colored squares around it getting progressively bigger. Once you hit the desired square on your zoom note the color of the square and it's size.

And finally, my question: Does anyone have any suggestions on how to make the filesize smaller, even if it's just a little bit?
(interlace vs non-interlace, GOP structure, quantize matrix, etc.. )

My thanks to you all in advance

[junkmalle]

Mask out the overscan area. That will reduce the picture content by about 20 percent -- you won't see it on TV anyway.

Use a variable bit rate.

I don't think VirtualDub supports it but a temporal filter can reduce noise thereby making the video more compressible. Use a 2D noise filter too.

[lordsmurf]

Well, as soon as you dump the interlace, you see immediate artifacts that cannot be ignored.

Dark scenes take more bitrate that light scenes.

Anything below x240 pretty much become unwatchable on a tv screen.

[pijetro]

Intension: #1. To burn multiple files to a non-standard vcd which I can play on my dvd player

Many players won't play non-standard VCD's. If your's does, than that's an exception..

The output format you're requiring, along with your intentions are quite odd..
IMHO, if you're concerned about filesize, then perhaps look into players that playback .WMV. Many nowadays seem to..More so than non-compliant VCD's..
This way, you can get much better quality, for the bitrate required..
Using the Windows media Encoder allows you to fiddle with numerous audio and video settings. More so than with Tmpgenc...

Good luck!!!

[RabidDog]

This seems a weird request
DO the sound in mono or joint stereo
turn the brightness even lower
lower the size even more. (100x80)
encode at a framerate of 23.97 (33% saving in bitrate).
All this will of course sacrifice whatever remaining quality you have (not much!).
If storing these avi's on your hard drive leave them as they are?

[Shadowmistress]

My intentions are to make the file the smallest possible size.
Yes, my dvd player plays mpegs on non-standard vcd's.
Are you saying that wmv's give you better quality than mpegs in general for the same filesize?

If I have a clear avi to start with, what noise reduction settings do I need to use in tmpgenc to get a more compressible file?

If I have a constant biterate of 225 that will give me a file size of just over 100 mb, what variable biterate settings do I need to ensure that the filesize will come out to 100 mb?

Masking and framerate are both great suggestions, but I haven't seen much difference between mono and stereo when it comes to size.

Thanks again for all your help.