Would q-pel be useful in my particular case?

[Ultimaty]

When I make backups of my DVDs, I encode at 720x480 resolution without any resizing or cropping, then I make the matroska to correct the AR. Since I'am encoding at 1:1, my guess is that I'd be better off with q-pel turned off, but I'm not that sure of myself... So what do you think?

I tried to get the answer in other threads, but doing it tends to bring me more questions than answers... :D

Thank you.

[Sharktooth]

Try it and, if you like the results, keep it... otherwise...

[Teegedeck]

I always like to think that the effect of QPel looks a bit like the effect of DC-precision in MPEG-2 and thus would make a good substitute for it. Use it.

[Splashdriver]

I also have a question about qpel (in combination with resolutions of 720x***). Does it make any sense to enable an option like qpel when the purpose is to view the movie on a 1 GHZ machine with 256 RAM (for the audio part that would be AAC HE-profile)?

Thanks in advance,

Splashdriver

[akupenguin]

1GHz is plenty, so the extra CPU time needer for qpel should make no difference to you. The only remaining issue is, does it improve compression quality for your movie? And the answer to that depends on the movie and the bitrate, but not on your playback setup.

[Splashdriver]

Well, I do understand that the visual benefits that Qpel might deliver is something you can't predict, so have to try it out for yourself to see whether Qpel might improve the image or not, ain't that right?

The reason I was asking is because I've read somewhere that (can't remember where or what thread at this moment) the higher the resolution becomes, the more CPU is required for decent playback. Now, since Qpel is an quite advanced tool and I'm planning on doing an anamorphic DVD-rip (720x***->1024x***)plus AAC-HE (which also required quite some CPU to playback smooth I've once read in the audio forum), I was wondering if this doesn't put to much pressure on a simple 1GHZ processor.

BTW, the bitrate I'm using is 3000 Kbps (CQM= EQM V3UHR).

Greetings,

Splashdriver

[SeeMoreDigital]

Ultimaty,

I guess whether to use Qpel or not would also depend on the bitrates you intend to use...

When encoding at 1:1 I've often found, the higher the bit-rate, the less you need to rely on tools such as Qpel and GMC (sometimes even b-frames)!

That said, I play the bulk of my encodes via hardware for viewing on an HDTV screen. Which is a more forgiving environment ;)


Cheers

[akupenguin]

My benchmarks:
(CPU = AMD Barton 2500 (1.8GHz), decoder = MPlayer/lavc/faad/xmga)
test video = XviD, 720x480x24fps, 2.5 mbit/s
with qpel, video playback takes 13.8% cpu
without qpel, video playback takes 9.5% cpu
HE-AAC 6ch takes 5.9% cpu
HE-AAC 2ch takes 2.3% cpu

These are average values; you'll see some slowdowns and/or frame dropping before hitting 100% average, but still you should have plenty of room to spare.

[SeeMoreDigital]

Interesting akupenguin,

What container did you use for your "load" tests?


Cheers

[Ultimaty]

I'm usually aiming somewhere around 1300-1400 kbps... I try to put 3 90 min movies on a DVD.

For playback, I use either 800x600 or 1024x768.

[Splashdriver]

Allright. Is it possible to have any foreknowledge to say whether or not it makes sense to use a number of 2 Bframes at a bitrate of 3000 Kbps and above?

It might be a lack of knowledge on my side, but may I ask what the container has to do with CPU load? Isn't it about the streams (and the decoders that are associated with it ofcourse) that be muxed inside a container which eventually define how much CPU-power is required for playback?

[edit:typo changed]

Greetings,

Splashdriver

[Teegedeck]

1) You're trying too hard to see a problem here; QPel, B-frames and AQ will only degrade a high-bitrate encoding like yours IF either you still have a saturated encode (quant=2, and that is hard to reach if you, for example, use Didée's SixOfNine matrix) or IF you encounter the rare case of a problematic movie. If not, they are tools that actually improve quality. Full stop. And I don't care who contradicts! Because this is a subjective statement. ;)

Use them all, be happy. :)

Don't toy with the B-frames defaults(!!!), QPel is only bad in some cases with very high compression / low bitrates.

Anyway, at low quantizers the differences will only be visible if you use a good TFT for watching your videos (like I do).

2) The splitter for the MKV container also takes a little CPU-power but the difference to AVI shouldn't be realizable.

[Ultimaty]

Many THX :)

Now I'm going for q-pel! :D

[Teegedeck]

Oh; and make sure you use XviD 1.1.

[Splashdriver]

Thanks. I guess making a movie to be processed by quart-pixel movement precision doesn't really have to hurt an movie in most cases. I only have to try it out to see how good it looks on my anamorphic, high bitrate Xvid encodes.;)

About: Use them all, be happy.

Allright, let's encode than.:D

Greetings,

Splashdriver.

[PiXuS]

Originally posted by Ultimaty
I'm usually aiming somewhere around 1300-1400 kbps... I try to put 3 90 min movies on a DVD.

For playback, I use either 800x600 or 1024x768.

I often see such statements and never really understand it. Why are people saying "I aim to produce encodes @ N bitrate"?

Unless I completely missed the point, wouldn't you want to to a simili-CBR encode only when you wish to stream the video? Otherwise you shoudl either 1) do a 2-pass / fixed size or 2) 1-pass / fixed quant encode?

Would there be other advantages of encoding @ a given bitrate other than if we need to stream?

I will be redundant here: why say "I only do HQ encodes @ 3000kbps" when if you do a 1-pass fixed quant encode (let's say q=2 with SixOfNine (overkill for the example)) you actually obtain a bitrate of 2423kbps... what gives to "force" a 3000kbps encode!?!?

[SeeMoreDigital]

Originally posted by PiXuS
... Why are people saying "I aim to produce encodes @ N bitrate"? If it's your intension is to put more than one Mpeg4 encode of differing run-times onto a DVD/RW, you've got to have some sort of target to aim for...

Unlike CBR, VBR encoding, makes much better use of all the available bits...

And it is possible to stream 2pass VBR encodes... I have some examples on my web site!


Cheers

[stephanV]

Originally posted by PiXuS
Unless I completely missed the point, wouldn't you want to to a simili-CBR encode only when you wish to stream the video? Otherwise you shoudl either 1) do a 2-pass / fixed size or 2) 1-pass / fixed quant encode?
You missed the point a little... :)

they mean a two pass at a given bit rate... which is VBR, not CBR.

Since bit rate is proportional to file size, there is no principle difference between encdoing at a target size or encoding at a target bit rate. (other than needing a bit rate calculator for the latter :) )

[PiXuS]

Originally posted by SeeMoreDigital
If it's your intension is to put more than one Mpeg4 encode of differing run-times onto a DVD/RW, you've got to have some sort of target to aim for...

Unlike CBR, VBR encoding, makes much better use of all the available bits...

Uh.. yeah. I think you didn't read my post properly.

Originally posted by SeeMoreDigital

And it is possible to stream 2pass VBR encodes... I have some examples on my web site!

Interesting, but I believe when dealing with streaming issues, it's better to use CBR as much as possible (much easier for the decoder to deal with it I think).

Originally posted by stephanV

You missed the point a little...

they mean a two pass at a given bit rate... which is VBR, not CBR.

Since bit rate is proportional to file size, there is no principle difference between encdoing at a target size or encoding at a target bit rate. (other than needing a bit rate calculator for the latter )


Oh... they meant a 2-pass for a given bitrate. Okay.. I thought they meant a 1-pass (CBR).

Bitrate is proportionnal to file size? Really? :rolleyes:

I still don't get why you would want a 2-pass w/target bitrate. But.. anyway.. it isn't really important.

[Splashdriver]

Hi,

I've finished my 2-pass encoding not too long ago and I'm pretty pleased with the resulting image quality. Settings that were used:

Koepi 1.1 Build

2-pass settings:

Target Size = 2850488 KBytes
Average Bitrate=3080 kBit/s

Profile @ Level= 5
ms= 6
VHQ = 4
VHQ bframes = 1
Chroma Motion
Turbo
Quantizer Restriction=2/31/2/31/2/31/
Trellis
Quarter Pixel
B-VOP's= 2/1.50/1
Closed GOV
CQM= eqm_v3uhr
Pixel Aspect Ratio= 65:45

Zones:

Start frame:175539
Q=20
Begin with keyframe
Greyscale encoding
BVOP Sensitivity:5

I've included a link to some screenshots in case someone might be interested. Click here (http://s11.yousendit.com/d.aspx?id=3ED734EA4E377525A28DE38595D22D7E) to download screenshots.

Regarding Qpel and AAC, they really slow down playback A LOT on my 1GHZ machine. I've tried to open task manager and shut down as many applications as possible and see if that solves the slow playback/out of synch problem, but it didn't(I mux my streams into MKV container). I tried to exclude the audiotrack and mux only video woth subtitles (and some attachments and stuff), video runs fine. I've also tried to mux the original 6ch AC3 with the videostream to see what happens; that resulted in less slower playback, but still not good enough:(. Is Qpel the guilty one at full DVD resolution?

[Splashdriver]

Here's a link to a small clip(qpel) (no audio included though). here (http://s11.yousendit.com/d.aspx?id=EE3683344BFEEFD31BB0E21D2FE77406)
Beware: clip is about 54 MB.

Greetings,

Splashdriver

[Teegedeck]

As you are at it now, how about comparing it with an encode using AQ? SixOfNine? The kitchen-sink? Whatever.

It ain't much sense in just nodding-off your encode as OK. More fun if you conduct your own little comparison, I'm talking of experience here. :)

[Splashdriver]

It ain't much sense in just nodding-off your encode as OK. More fun if you conduct your own little comparison, I'm talking of experience here.

You're probably right there, but I'm searching for acceptable quality (fully based on personal taste) without having to suffer from very bad computer performance. I think I might have been too enthusiast selecting features that don't work right for me. I'll will redo a 2nd pass without qpel so I can compare the 2 files made. Size is not a real problem here, it's performance that stresses me the most;).

Greetings,

Splashdriver