TmgGenc: Same bitrate but different filesizes

[jimA]

I have this clip.

Using TMPG (I tried different versions, including Xpress 3.0).

Using FitCD I find out that I should use a bitrate of 2345 to make the filesize 793mb.

using Xpress3.0:
Encoding with CBR I get a filesize of 793MB.
Encoding with vbr, quality High, file size=775
Encoding with vbr, quality Low, file size=781

Shouldn't it be the same size ? This has happened to a lot of different clips

Help....

/jima

[flaninacupboard]

TMPGenc does have a tendency to produce files slightly too small. enable it's logging and then read the log file, you'll see why

[jimA]

thx for the tip about logging. I tried it but I don't see why...

What am I looking for in the logfile ?

and why is it too small on some files, and not others ? Is there any way I can work around this bug ?

/jima

[flaninacupboard]

well in the log you'll see "predicted frame size xxxxxxbytes actual frame size xxxxxxbytes" these differences are sometimes quite big, and ad dup to a lot of thousands of frames. the most accurate you'll get on filesizes is using a 2-pass VBR, but obviously this takes twice as long to encode. you can also set your average about 5% above what it should be that'll get you close.

[jimA]

I am always using 2 pass vbr.

Most of the times I get exactly the size fitCD predicted. But some clips behave strangely, and I was trying to find out beforehand which clips were weird. And maybe what to do about it.

/jima

[flaninacupboard]

you'd need to speak to the authors diretly to verify the exact problem. it's going to be something to do with the way it judges scene complexity. you'll probably find the troublesome clips all have dark scenes, or colour saturated scenes, or very detailed scenes. there's something they have in common that's tripping the encoder, really difficult to analyse from a distance and without a deep knowledge of the programs' workings

[cd090580]

It's normal for vbr files to be smaller than cbr ones because with vbr some scenes need lower bitrate so it reduce the filesize.

With vbr you can get better quality with smaller files but it takes minimum twice the time of a cbr encode.

[bugster]

It's normal for vbr files to be smaller than cbr ones because with vbr some scenes need lower bitrate so it reduce the filesize.

.

VBR, with the Average bitrate set to the same value as used for a CBR encode of the same source SHOULD give exactly the same file size.

It doesn't always work out exactly like this as most encoders don't achieve the exact average with VBR, but they are usually close.

[Gazorgan]

At least TMPGEnc misses smaller, if you hit 30 MB over, you'd be pissed.

I still use TMPGEnc. I was giving ProCoder a whirl, but it consistantly fails on at least 60% of my files when batch encoding. I was doing some 50 minute AVI's and I was getting file sizes from 200 to 980 MB's, when I should be right at 970 MB. TMPGEnc all were within 30 MB's of each other (file sizes vary somewhat due to variable lengths).

Mainconconcept hits the same file size range, but it's a HUGE pain in the arse to reset everything everytime I change input files(for batch encoding).