What is the point of Nth pass?

[unimatrixzer0]

For a while now I've been doing First Pass, then Nth (+2) Pass, so a total of 3 Passes. The only reason I've been doing 3 is because I was under the impression that it produces a better looking video w/ Divx 5.x.

My question is do the extra passes deal with compression and trying to produce a more compressed file, or does it effect the quality of the video. Because if the 3rd pass doesn't make the video look any better and just helps make the output file small then I'd rather not have to waste that time on a 3rd pass.

Thanks.

[Soulhunter]

Simple answer... Test it out !!!



Source:

Chaser Trailer - MPEG1 (CG) / 1:19 min / 25fps / 384x288



MultiPass 250 kbps / No Psy. / Bidi Enc. / Standard

Pass1:
Time: 03:02 min. / Size: 14.090.240 Bytes / Avg. PSNR: 40.24

Pass2:
Time: 02:52 min. / Size: 16.564.224 Bytes / Avg. PSNR: 40.46

Pass3:
Time: 02:51 min. / Size: 16.564.224 Bytes / Avg. PSNR: 40.55


MultiPass 250 kbps / Fast Psy. / Bidi Enc. / Standard

Pass1:
Time: 03:02 min. / Size: 14.090.240 Bytes / Avg. PSNR: 40.24

Pass2:
Time: 03:28 min. / Size: 16.566.272 Bytes / Avg. PSNR: 40.31

Pass3:
Time: 03:26 min. / Size: 16.562.176 Bytes / Avg. PSNR: 40.22


MultiPass 250 kbps / Fast Psy. / Bidi Enc. / Slowest

Pass1:
Time: 15:22 min. / Size: 14.090.240 Bytes / Avg. PSNR: 40.54

Pass2:
Time: 15:29 min. / Size: 16.562.176 Bytes / Avg. PSNR: 42.02

Pass3:
Time: 15:43 min. / Size: 16.560.128 Bytes / Avg. PSNR: 41.17


MultiPass 250 kbps / Slow Psy. / Bidi Enc. / Standard

Pass1:
Time: 03:20 min. / Size: 14.090.240 Bytes / Avg. PSNR: 40.24

Pass2:
Time: 04:18 min. / Size: 16.568.320 Bytes / Avg. PSNR: 40.19

Pass3:
Time: 04:28 min. / Size: 16.560.128 Bytes / Avg. PSNR: 40.10


MultiPass 250 kbps / Slow Psy. / Bidi Enc. / Slowest

Pass1:
Time: 15:32 min. / Size: 14.090.240 Bytes / Avg. PSNR: 40.53

Pass2:
Time: 15:50 min. / Size: 16.562.176 Bytes / Avg. PSNR: 41.93

Pass3:
Time: 16:51 min. / Size: 16.560.128 Bytes / Avg. PSNR: 41.09


But the results could change with other sources... ;)


Bye

[bond]

3rd pass makes sense quality-wise in divx5 (surely not speed-wise :D )

but a good codec should be able to do the same thing with two passes (like xvid ;) )

[Soulhunter]

Ok, my first sample could be misleading... ;)

Here is another one !!!



Source:

The Matrix - Lobby Shootout / 3:07 min. @ 25fps / 1024x576 pix. (Lanczos)



MultiPass @2500 kbps / No B-Frames / No QP / No PVE / Standard
2nd Pass: Size: 58.718.208 Bytes / Avg. PSNR: 43.28 / Time: About 04:02 min. (2600XP)
3rd Pass: Size: 58.677.248 Bytes / Avg. PSNR: 43.29 / Time: About 04:11 min. (2600XP)

MultiPass @2500 kbps / No B-Frames / No QP / Fast PVE / Standard
2nd Pass: Size: 58.673.152 Bytes / Avg. PSNR: 43.03 / Time: About 04:57 min. (2600XP)
3rd Pass: Size: 58.681.344 Bytes / Avg. PSNR: 43.04 / Time: About 05:02 min. (2600XP)

MultiPass @2500 kbps / No B-Frames / No QP / Slow PVE / Standard
2nd Pass: Size: 58.742.784 Bytes / Avg. PSNR: 42.74 / Time: About 07:19 min. (2600XP)
3rd Pass: Size: 58.667.008 Bytes / Avg. PSNR: 42.74 / Time: About 07:26 min. (2600XP)


MultiPass @2500 kbps / No B-Frames / QP / No PVE / Standard
2nd Pass: Size: 58.679.296 Bytes / Avg. PSNR: 42.76 / Time: About 14:13 min. (2600XP)
3rd Pass: Size: 58.703.872 Bytes / Avg. PSNR: 42.76 / Time: About 14:17 min. (2600XP)

MultiPass @2500 kbps / No B-Frames / QP / Fast PVE / Standard
2nd Pass: Size: 58.726.400 Bytes / Avg. PSNR: 42.39 / Time: About 14:49 min. (2600XP)
3rd Pass: Size: 58.679.296 Bytes / Avg. PSNR: 42.39 / Time: About 14:52 min. (2600XP)

MultiPass @2500 kbps / No B-Frames / QP / Slow PVE / Standard
2nd Pass: Size: 58.728.448 Bytes / Avg. PSNR: 42.12 / Time: About 16:27 min. (2600XP)
3rd Pass: Size: 58.710.016 Bytes / Avg. PSNR: 42.12 / Time: About 16:28 min. (2600XP)


MultiPass @2500 kbps / No B-Frames / No QP / No PVE / Slowest
2nd Pass: Size: 58.673.152 Bytes / Avg. PSNR: 43.60 / Time: About 28:43 min. (2600XP)
3rd Pass: Size: 58.697.728 Bytes / Avg. PSNR: 43.61 / Time: About 28:45 min. (2600XP)

MultiPass @2500 kbps / No B-Frames / No QP / Fast PVE / Slowest
2nd Pass: Size: 58.744.832 Bytes / Avg. PSNR: 43.15 / Time: About 28:48 min. (2600XP)
3rd Pass: Size: 58.679.296 Bytes / Avg. PSNR: 43.17 / Time: About 28:49 min. (2600XP)

MultiPass @2500 kbps / No B-Frames / No QP / Slow PVE / Slowest
2nd Pass: Size: 58.730.496 Bytes / Avg. PSNR: 42.98 / Time: About 30:59 min. (2600XP)
3rd Pass: Size: 58.740.736 Bytes / Avg. PSNR: 42.99 / Time: About 31:00 min. (2600XP)



Bye

[DigitAl56K]

The benefit of Multipass is not so much that you expect better PSNR, but that you expect a greater quality consistency throughout the entire file. I.e. you do not watch it and think "Wow you can see a lot of blocks in this scene, but the last scene looked really good..." - which can happen in 1-Pass mode.

You should read through the Multipass section of the DivX Users Guide, it explains some of the principles behind multipass and the benefits you will typically see from it.

[Sharktooth]

3rd pass is also useful to reallocate bitrate manually thru the EKG.
As D56K said it smoothes out the blockiness and weird stuff that may happen in a 1-2 pass encoding.
3rd pass is "optional" and should be used only when needed (if you care about the encoding time).