Single Pass or Two Pass?

[miniyoyo]

I use Xvid to encode movie(.vob), using the Autogk. However, doing a two pass encode need 5-6 hours(movie is two hours length, encoding at 640*480), it is painful. I notice that there is an option "Target Quality" which is using single pass. Will the motion scene of the movie degrade if using single pass? Also, will the final file size terrible? (ie. Will the file size bigger than that of the two pass very much?) Hope to hear from those who has such experience. Thx..

[Teegedeck]

No, the only setbacks of single-pass, constant-quality encodings are
- You have no precise control over the output-size; your resulting file may be just a tad too big to burn onto a CD-R. On the other hand you can determin a feasible quantizer to use with a tool called 'Enc' quite precisely enough.
- Whenever you aim for a fixed filesize / don't have space in abundance (definition of 'space in abundance': 1 DVD-R per movie ; i.e. you can encode at constant quantizer=2) a two-pass encoding, if done correctly, will yield a slightly higher perceived quality than single-pass. Because a) constant quant undershoots in most cases as you can't afford to overshoot; hence you don't reach the lowest quantization possible for the aimed-at filesize and b) if you use just a little bit of curve-compression (about 10% perhaps) in two-pass you have a good chance that some frames where you don't realize it will be compressed with quant=5 while others where you do realize the diference will be encoded at quant=3. That's theory though and might not really work out that way.

As you see; the difference gets all the less important the more space/quality you want to invest into the encoding.

[miniyoyo]

Since I always encode movie which is of intensive action/motion, will single pass result in the badly compressed motion screen? Previously with Divx 5.2.1 that was the experience. I feel ill when seeing those broken screen..

[aeternitas]

Quality takes time.

[Morte66]

How much compression do you want?

If you are looking for "near-as-damn-it-perfect" quality backups, quality based encoding at 100% will do it and give you a file around half the original size. You won't notice a difference between single and double pass. [At this level, resizing DVD material to 640x480 is going to do cost more quality than your choice of Xvid compression settings.]

But the more compression you go for, the bigger the difference between single and dual pass. If you want to put movies on a CD or two, dual pass will be visibly better.

And then there's the whole "personal taste" thing"... I would suggest running some tests -- rip a two minute trailer, and run it through AGK at various settings to see what you think.

[Teegedeck]

Since I always encode movie which is of intensive action/motion, will single pass result in the badly compressed motion screen? Previously with Divx 5.2.1 that was the experience. I feel ill when seeing those broken screen..
Inform yourself about the difference between single-pass CBR and single-pass quality-based. :search:

[jsquare]

I use Xvid to encode movie(.vob), using the Autogk. However, doing a two pass encode need 5-6 hours(movie is two hours length, encoding at 640*480), it is painful. I notice that there is an option "Target Quality" which is using single pass. Will the motion scene of the movie degrade if using single pass? Also, will the final file size terrible? (ie. Will the file size bigger than that of the two pass very much?) Hope to hear from those who has such experience. Thx..
After months of trial and error I opted for 1-pass quality based encodes with GK, space is not an issue since I'm using DVD-R media(no more CDs please) and stored them on HD so I can streamed to an Pinnacle Show Center/XBox. The resulting quality IMO is better than 2-pass, some 2hrs movies will take very little space(less than 700MB) while others will be twice as big.
If you want my settings for quality based encodes of around 70%(~Q=2.86) let me know and will post them.

[miniyoyo]

Well, for 120 minutes movie(DVD .vob format, most likely 4G size), if using Autogk to encode(Quality 75% which is the default setting, the tutorial said it is Quat 4), what seem to be the output file size? :confused:

(Thx jsquare, but I am still struggling with Autogk, GK is so professional)

[manono]

(Quality 75% which is the default setting, the tutorial said it is Quat 4),

Oh, and just where does it say that? It should be a bit lower than ave. quant 3, although the B-Frames will skew that a bit, if you check in DRF Analyzer.

what seem to be the output file size?

As Teegedeck said earlier, there's no way to tell in advance, even if you know the movie's length, unless you do a compression test with Enc or GKnot. Each movie compresses differently, and a Quality encode for the same percentage for different movies will produce different sized AVIs, and sometimes very differently sized AVIs. Quality Mode is for when you don't care much about the final size, if burning to DVDR, or keeping on the hard drive, for example. If you want a specific file size, then you had better use the 2-pass Target Size.

[Teegedeck]

Yes, everyone who wants to encode at fixed quantizer but still cares about filesize must use Enc or other other means of filesize-prediction.

There's no point in asking what quality-setting you should use, miniyoyo.