Xvid 1 pass vs 2 pass

[ginjuice]

Hi, I've just registered, I'm a longtime reader and firsttime poster.

A friend of mine is experimenting with 1 pass XviD encoding on HDTV streams, he wouldn't give me the specifics really but he said he was able to make a 1 pass encode look the same as a two-pass encode. From what I've read here and the faq, that would pretty much be impossible but I saw his shows and they look ok.

My question is based on the final avi that's produced, is there a way to tell or is there a program that I can use to tell if an encode was done using a one pass method or a two pass method? I would really like to show him up. :)

I'm sorry if you need more information. He won't given me any more specifics (as to what filters, etc he's using) that would help you experts but if there is a specific question I can ask....if only to help you guys get a clearer picture, let me know.

To all developers out there, keep up the excellent work!

[sysKin]

My question is based on the final avi that's produced, is there a way to tell or is there a program that I can use to tell if an encode was done using a one pass method or a two pass method? I would really like to show him up. :)

Ffdshow decoder, then its options -> OSD -> Quantizer, and also Frame Type.

If quantizer is constant for all p-frames and i-frames then he used single-pass constant quality, and indeed his encodes will look perfect (in fact better than 2-pass) but he can't predict filesize.

If quantizer stays roughly the same, and fluctuates a bit (say 3..4) then he used 2-pass.

If quantizer fluctuates like crazy and goes from 1-2 at still scenes to 10-15 at high motion scenes, he used single-pass CBR and it looks horrible.

And finally, if the quantizer fluctuates between 1 at still scenes and, say, 4 at high motion, then it looks good but only because bitrate is huge, and he wasted most of the filesize.

remember to look at p-frames and i-frames only.

[raeltheimperialaerosolkid]

Syskin, your explanation about the reasons of making 1 or 2 pass should be sticked in every guide and FAQ on XviD. You can't even imagine how many encoders (intended as people that encode) I knew that asked "What is the best bitrate for best quality?". They only aimed for quality and not for a specific filesize....but simply they didn't know this and thought that they FIRST had to find a right bitrate THEN to make a 2 pass encoding targetting that bitrate.
They were probably misleaded by the high configurablity of XviD... So... forgive my question that may seem dumb... What's the point of allowing a target bitrate for a 2 pass encoding? The simple filesize target wouldn't be enough?

Yours...

Rael