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View Full Version : Bframe and quality improvments


FunMan
19th January 2003, 21:17
Hi,

I'm encoding my Queen concert yet (have you ever tried to encode "The Freddie Mercury Tribute Concert" on 2cd? This is the most difficult source I've ever compressed!) but during a "pause" I encoded a chapter from Matrix (one of the firsts chapters, when Trinity run away from Agents). First of all I found the chapter very compressible, with or less bframes.

As I said other time (but I think that it's better to repeat) I use XviD as ISO MPEG-4 codec in a ISO mp4 stream with MPEG-4 aac audio. Using an iso mp4 player (Envivio TV) I haven't any kind of post processing on the movie so watching the *raw result* of the encoding I try to find for the proper source the *best* encoding settings.

On Matrix I noticed a thing. When Trinity has knocked down the various policeman and she's speaking at cellular phone with Morpheus, using bframes the image is ok but if I don't use they the background image (a wall?) seem to be composed by varios "floating macroblock". I don't know how to describe it....

I noticed a variant form of this problem also on other source. For example encoding a special insert from "Queen Greatest Video Hits I" named "Inside the Rhapsody" (a very statical movie, 27 min of interview, easily compressible) I see that not using bframe the image has a slow and progressive quality degradation as long as not arrives the new and fresh iframe. Using bframe the image quality remains the same.

I'm the only one that has noticed this quality improvment of bframes?

Curious,

bye
FunMan

MfA
20th January 2003, 21:48
Sounds like error accumulation from having too long a string of motion compensated MBs, b-frames makes the strings shorter so lessen the problem, do you see anything if you encode to avi and watch with the xvid decoder?

FunMan
20th January 2003, 22:03
I usually use mp4, not avi. However I'll make some tests soon....

bye
FunMan