libavc vs xvid

[Razorblade2000]

I can't find a single test on the web... what are your experiences concerning quality and speed?

[mikeX]

afaik ffvfw = libavc, so the latest doom9 codec comparison (http://www.doom9.org/codec-comparisons.htm) should give you some clues.
i dont' expect the speed comparison to be that accurate though.

[spyder]

In my recent experience(which is still very limited mind you), I have found lavc to be better for video that is really difficult to compress. Where xvid blocks up or becomes icky lavc seems to preserve the image more. Though both codecs still don't work well on these sources without more bitrate. As far as speed, I find xvid to be faster due to the "turbo" mode etc. Just my 2 cents...

[Mosu]

Originally posted by spyder
As far as speed, I find xvid to be faster due to the "turbo" mode etc. Just my 2 cents...

If you want to compare speed then don't compare xvid's "turbo" mode with lavc's standard options. Compare the speed at which you get equal results, that should be better. Or try to get the highest speed from each codec (although that would mean one pass, no MV, bad macro block decisions etc).

With a lot of advanced options on _both_ codecs you get... well... Sometimes lavc is faster, sometimes xvid (because you can argue that some lavc options do not really yield better-looking results but slow it down a lot).

Just another 2 cents.

[spyder]

Well, I haven't yet found a similar option to Turbo in lavc. AFAIK turb disables a lot of options on the first pass that make a very slight difference to quality. If you can do the same in lavc then please tell me how :)

[frodoontop]

Turbo doesn't change the speed of the first pass, but only that of the second pass as far as I know. By default xvid uses fast first pass, which you can disable, but fast first pass has nothing to do with turbo mode I believe.

[mikeX]

Turbo has nothing to do with 'Fast first pass', and all in all doesn't offer that much of a speed enhancement.
From The Unofficial XviD FAQ (http://www.vslcatena.nl/~ronald/docs/xvidfaq.html)
-Turbo ;-): This setting skips some search techniques when using Qpel or B-frames to speed it up a bit. Without those options on it has no effect at all. The impact on quality is negligible.
'Fast First Pass' is a whole other thing, it skips some 'advanced' settings, like VHQ, Q-PEL, Trellis, etc, for which the 2nd pass compensates.
From The Unofficial XviD FAQ (http://www.vslcatena.nl/~ronald/docs/xvidfaq.html)
-'Full quality first pass':By default XviD switches certain options off in the first pass to speed it up a bit. The options that are switched off are not really necessary for a 'normal' first pass (normal as in: you don't keep it afterwards) and turning them off can increase encoding speed considerably.

The difference in speed between 1st and 2nd pass is substancial if you happen to use these options.

[spyder]

Ok, I stand corrected then. I really should keep up with xvid more :/

I guess I was thinking of 'Fast first pass'

[shevegen]

Gosh I couldnt even contribute at all due to my limited knowledge. But, i guess, having an up-to-date FAQ about xvid and similar is really important.