M2V file size much smaller than projected Bitrate

[liverkick]

This is an offshoot of my first post, thought Id start a new one as this is starting to baffle me a bit.

Ive been using Tmpgenc Plus to encode several 24 minute AVI files to DVD. I planned on using 4 to a disc for a total of 93 minutes. The bitrate calculator projected roughly a 6300 average, which I used (along with 1000 min, 9200 max).

But my first four encoded m2v files ended up being 690 mb, 687 mb, 656 mb, and 659 mb to be exact. Now Im pretty new at this stuff but is this normal?

I used a program called MPEG Inspector that says the Nominal Bitrate of the m2v is 9,200 kbit/s. And the bitrates average is 7.257. This is only for the first 11 minutes I guess, since the trial version is limited in how much it can analyze.

Anyhow I'd appreciate any insight on this, thanks.

[jimmalenko]

The only thing I can think of is that perhaps your source doesn't require that much bitrate being thrown at it. One would imagine that if it can use 5000kbps to describe a second of footage exactly like the original, it would use 5000kbps and not 6300kbps I would've thought. I'd look more towards the quality aspect - is it up to scratch quality-wise ?

[liverkick]

Thanks for replying to this Jimmalenko, the crickets were disconcerting.

I kinda found an answer, you're definitely right that the bittrate wasn't getting thrown at it. I ran the m2v file in another Bitrate viewer program and it was only about 4300 average for the first 18 minutes or so, which would explain the file size. The weird thing is Mainconcept is willing to throw a little more ave bitrate at the file than Tmpgenc for some reason. It'll go up to 5000 instead. Neither program hits the requested 6000+ mark though.

As for the quality its kind of tough for me to compare as its traditional animation so the detail may not be as noticeable as live action video, but its looks pretty close to the source file (630x360) from what I can tell, just a tad blurrier. Then again my eye for this isnt exactly expert. Im happy enough so I cant complain.

I was probably over doing it with 6000+ 2 pass anyway (its my first try at this afterall ). I just wish I knew why the programs are essentially ignoring my requested average for these avis. Perhaps hand drawn animation requires less bitrate for some reason, it only needs a certain amount for accuracy like you were saying?

I just hope nothing is wrong with my CPU, Mobo or RAM thats causing funky things to happen when I try to encode stuff.

[jimmalenko]

One test you could do (just for experimentation's sake) is to encode your AVIs again using CQ mode, and set the quality to 100. Set the max and min to the same values you used in the first case. This should only use as much bitrate as required to suitably represent the source video, and I'd be interested to see what sorts of bitrates it uses in this scenario, and whether the end file-sizes are similar to those that you received using 2-Pass. That should give you a decent indication of if the 2-Pass is acting normally, anyway.