Quantcast KVCD: Advantages of a Tight GOP ? - digitalFAQ.com Forums [Archives]
  #1  
12-12-2002, 09:46 AM
Jellygoose Jellygoose is offline
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Hi kwag...

what are exactly the advantages of using a "tight" GOP or using a loose(?) GOP?
Why did you change the GOP of the kvcdX3 Templates for example...?
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12-12-2002, 10:53 AM
kwag kwag is offline
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All KVCD PLUS, including the LBR, use the same GOP. 1, 18, 3, 1, 18.
The big difference is in the number of B frames, where I used 3 instead of 2. This gives greater compression than the default value of 2. This GOP works great with our Q. Matrix. The standard GOP, if used with our matrix, creates much larger files. When used with CQ_VBR, this combination of GOP and matrix gives the best size/quality/compression ratio of all settings/templates I've tried.

-kwag
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12-12-2002, 12:10 PM
Jellygoose Jellygoose is offline
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Why did you decrease the max. number of frames value to 18 ? It used to be 48 as I remember...
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12-12-2002, 01:22 PM
kwag kwag is offline
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Quote:
Originally Posted by Jellygoose
Why did you decrease the max. number of frames value to 18 ? It used to be 48 as I remember...
Yes, I decreased it because at 48, some people's DVD players showed a "Ghost" effects and/or "flashes" when playing back the KVCD's. The GOP was just too long. Great compression, but quality suffered. The way it's set now, is a good compromise between compression/quality.

-kwag
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12-12-2002, 03:34 PM
Jellygoose Jellygoose is offline
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So basically the higher the value for "Max Frames per GOP" is, the higher compression, and less quality, + more weird effects... ?
Am I right? So maybe I seek a compromise in between, something like GOP 30 or 25? would that be ok?
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12-12-2002, 06:36 PM
kwag kwag is offline
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Quote:
Originally Posted by Jellygoose
So basically the higher the value for "Max Frames per GOP" is, the higher compression, and less quality, + more weird effects... ?
Am I right? So maybe I seek a compromise in between, something like GOP 30 or 25? would that be ok?
The best thing to do is to try it out yourself. Try 1, 36, 3, 1, 36. If that works on your DVD player, you'll have a hell of compression
That works for me, at east on all my DVD players. And I've been seriously considering making these values permanent
The difference in size, for example on a prediction clip at 704x480, is ~1MB smaller per 90 second sample without affecting quality . So on a 120 minute movie, you would have an extra ~80MB, and that means better quality/space ratio. Give it a shot

-kwag
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12-13-2002, 03:26 PM
black prince black prince is offline
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Hi Kwag,

Kwag wrote:
Quote:
The best thing to do is to try it out yourself. Try 1, 36, 3, 1, 36. If that works on your DVD player, you'll have a hell of compression
I tried 1, 48, 3, 1, 48 and it plays fine! This compression gave me alot
of room to increase the CQ. Thanks. I usually play LBR's on my PC and
x3's on the stand-alone DVD player.

-black prince
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12-13-2002, 03:56 PM
jamesp jamesp is offline
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What would these values be in PAL? I noticed in PAL the Max Frames per GOP is set to 15

Jim
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12-13-2002, 05:19 PM
kwag kwag is offline
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Hi jamesp,

You can use 1, 36, 3, 1, 36 in PAL too. I didn't notice any difference from 30 to 36 in PAL. So use 36.

@black prince,

Don't go overboard with the long GOP
At 48, it's a great compression, but picture starts to fade and you get flashing effect every time a new I frame is inserted in the GOP. This is noticeable on some DVD players (most) but not all. I would stick to 36, which would guarantee one new I frame at least every 1.5 seconds. Remember, you also have 3 B frames. So each GOP would look something like this:

IBBBPBBBPBBBPBBBPBBBPBBBPBBBPBBBPBBBI........

Where if you use 48, it would look like this:

IBBBPBBBPBBBPBBBPBBBPBBBPBBBPBBBPBBBIBBBPBBBPBBBI........

And you'll have a new I frame every 2 seconds. Too long for some DVD players, and a "flashing" or "pumping" effect will be seen.

Note: For Anime type movies, you'll get better results with shorter GOPs. I would use 1, 12, 3, 1, 12 for Animes.

-kwag
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  #10  
12-13-2002, 05:23 PM
black prince black prince is offline
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Hi Kwag,

Kwag wrote:
Quote:
@black prince,

Don't go overboard with the long GOP
At 48, it's a great compression, but picture starts to fade and you get flashing effect every time a new I frame is inserted in the GOP. This is noticeable on some DVD players (most) but not all. I would stick to 36, which would guarantee one new I frame at least every 1.5 seconds. Remember, you also have 3 B frames. So each GOP would look something like this:
You read my mind. I was going to ask how far is too far.
I can live with 1, 36, 3, 1, 36 and still be happy with the compression.
There are times when I like to play LBR videos on my stand-alone DVD
player and from what you're saying there should be no trouble.

-black prince
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  #11  
12-13-2002, 05:28 PM
kwag kwag is offline
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And with 1, 36, 3, 1, 36, the LBR encodes should look better, because it allows for a higher CQ_VBR. Even at 180 minutes, it should look better than the original 180 minute "The Green Mile" samples
Hell, I did a test with "Red Planet" at 528x480 target for a single CD-R with this GOP, and it looks the same as 1, 18, 3, 1, 18 but file size is much smaller. "Red Planet' looks GREAT on one CD-R with the x3

-kwag
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12-13-2002, 07:55 PM
syk2c11 syk2c11 is offline
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Hi Kwag,
So are official KVCD templates (in download page) adopting these new GOP (1-36-3-1-36), for example KVCDx2 Plus (704x480)? or it is just a test? Also, is this new GOP applicable to KDVD (still being compliant)?
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12-13-2002, 10:11 PM
kwag kwag is offline
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Quote:
Originally Posted by syk2c11
Hi Kwag,
So are official KVCD templates (in download page) adopting these new GOP (1-36-3-1-36), for example KVCDx2 Plus (704x480)? or it is just a test? Also, is this new GOP applicable to KDVD (still being compliant)?
If I get good reports from many people, regarding same compatibility as the shorter GOP, YES! I will change the GOP on all templates. I am having excelent results. I tried the LBR and the x3 and the results are just perfect. Same quality as before using the same reference CQ_VBR value, which means that for the same material to fit on X number of CDs, the quality will be higher because we can increase the CQ_VBR value. So this adds up to a choice of longer play time per media with same quality as before, or same play time as before but higher quality. It's your call
For KDVDs, we must keep using a max number of frames per GOP of 18 or 15 for PAL. There's no way around that. It's part of DVD specifications.

-kwag
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12-14-2002, 08:06 AM
mfb mfb is offline
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Last night i encoded 'Spiderman' (PAL, 116 min.) which has some high action scenses in two flavours: target 1 CD-R90

The first was using the 352x288plus template:
got some mosiquitos and not that sharp (300-1800, CQ_VBR 30)

and the second was a modified x2-template:
resized to 480x576, 'Output YUV data as Basic...' unchecked, 300-2300, CQ62, GOP 1, 9, 2, 1, 25, cutted some credits
a way better: much sharper, no blocks, no mosiquitos

so i've tried the different direction, using the x2-template which gives the longest playtime per filesize and tried to 'tighten' it's loose gop for action scenes and it works fine for me...116 min action-movie in high quality on on CD-R makes me smile...

regards, ***mfb***
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12-14-2002, 09:33 AM
kwag kwag is offline
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Hi mfb,

Try your Spiderman again with your same 300-2300 and same CQ_VBR, but use 1, 36 ,3 ,1 ,36. Your quality should still be the same, but your file size will be way lower. I assume you used CQ_VBR? Because you mention CQ62 and that would mean you used the old original templates and not the PLUS. The quality of the PLUS templates is way better than the original templates.

-kwag
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  #16  
12-14-2002, 10:03 AM
syk2c11 syk2c11 is offline
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Hi Kwag,
Having mentined "Plus" templates, there is no "Plus" for KDVD, right? I can see KDVD (Full-D1) is still using CQ not CQ_VBR.
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12-14-2002, 10:48 AM
kwag kwag is offline
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Hi syk2c11,

No, there are no PLUS. They are just KDVD templates
I still have to test CQ_VBR with those templates, because I wanted to use CQ_VBR there too. But CQ_VBR has a different scale (value) with our matrix, and I haven't done that test yet to find the minimal CQ_VBR value to set as default. Maybe I'll work on that this weekend
Anyway, the correct way to use any KVCD templates, including the KDVDs, is with file prediction, using SansGrip's KVCDPredictor.

-kwag
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  #18  
12-14-2002, 11:24 AM
mfb mfb is offline
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Quote:
Hi mfb,

Try your Spiderman again with your same 300-2300 and same CQ_VBR, but use 1, 36 ,3 ,1 ,36. Your quality should still be the same, but your file size will be way lower. I assume you used CQ_VBR? Because you mention CQ62 and that would mean you used the old original templates and not the PLUS. The quality of the PLUS templates is way better than the original templates.

-kwag
Hi Kwag,
No, what i used was the 'old' x2-template with CQ cause it's the only way to fit a whole movie on one CD-R but i've followed your adivse and tried the gop 1, 36 ,3 ,1 ,36 on the x2-704x576plus template and the x3-MPEG1-template (resized to 480x576)...my results for 60 secs prediction-clips:

704x576plus (300-2500. CQ_VBR12): 10.041 kb
704x576plus (300-2300, CQ_VBR12): 9.873 kb (your recommendation)
x3-MPEG1 (300-2300, CQ_VBR16): 11.172 kb

I guess, i shouldn't lower the CQ_VBR even more
No way to fit more than ~85 min. on one disk with the new plus-templates, but i did it with the old x2-template like mentioned above for the movie 'Spiderman'.

You told us, your were able to fit the whole movie 'Red Planet' (using the x3-template) on a single disk. Can you give me some details?

regards, ***mfb***
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  #19  
12-14-2002, 11:34 AM
kwag kwag is offline
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Hi mfb,

You must use file size prediction. Look at the links under Q-9 here: http://www.kvcd.net/forum/viewtopic.php?t=68 and don't use the old templates. Use the PLUS templates.

-kwag
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  #20  
12-14-2002, 06:57 PM
jamesp jamesp is offline
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Well it seems to work for me! Just done Primal Fear with no smoothing or anything at 544x576. With Max frames per gop set to 36 the encode came out 110mb less overall. I can't tell any difference on my player. Strangely though, i did a full screen DIVX encode and it came out very slightly larger. Will try a TV capture shortly.

Can I use this with the MPEG2 544x576 template?

Jim
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