Divx 5 and long movie files

Mercutio

Fatwah on Western Digital
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I know I'm not the only person here who encodes video.
Has anyone else here noticed that divx 5 seems to have a floor for file size when encoding at low bit-rates?

When I encode single files longer than 120 minutes, even with no audio, using vdub or tmpeg or even Premier, I end up with a file of around 800MB, no matter how low it set the bit rate or how much noise reduction or temporal smoothing (tools to make individual frames smaller) I do.

As an extreme example, I recorded a 2-hour and 1 minute MPEG1 sample of the blue screen my VCR shows when it has no other input - quite possibly the easiest thing I could possibly record. No audio at all. I encoded the MPEG using virtualdub on a couple of different machines using Divx5 Pro using different size-reduction techniques and a very reasonable 250kb/s bit-rate.
By my calculations, the file should've been about 225MB.

The smallest result I got was 760-something megs.

Anyone else run into this or anything like it?
 

blakerwry

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you need to adjust your quantizer under advanced perameters... these are what really set your bitrate. The lower the Quantizer number, the worse the quality... so change the default 2/12 combo to something like 6/24...

and/or try using 2 pass. The 1st pass will let the 2nd pass know what the apropriate quantizer should be vs the 1 pass mode just guessing.


You could also adjust your key frame rate.. although I have found that this normally doesn't make much of a difference in movies.

and if you have any static or pixilation, you might want to run everything through a smoothing filter just for better compressibility.
 

blakerwry

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woops.. should have proofed that.... I meant to say the lower the number, the better the quality..... quantizer 1 (or was it 0) is the best image quality, while higher numbers result in worse quality
 

blakerwry

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also, another thing to think about (not sure if you're aware) is the number of macro blocks you have in your video... DIVX devides the screen into 16x16 pixel blocks called macro blocks...

If you make your video resolution evenly divisible by 16 pixels then you will achieve a better quality to file size ratio.
 

blakerwry

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man, im inflating my count by the moment...


a couple of other things.. RC averaging period seems to work best if set to half the number of frames you intend to encode....


And the mpeg4 tools at the beginning (GMC, B-Frames, and Q-Pel) have all been shown to increase file size...


hmmm.. ah... are your performance/quality settings set to "slowest"? That's about the only other thing I can think of to help you out.
 

SteveC

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Mercutio said:
I know I'm not the only person here who encodes video.
Has anyone else here noticed that divx 5 seems to have a floor for file size when encoding at low bit-rates?

When I encode single files longer than 120 minutes, even with no audio, using vdub or tmpeg or even Premier, I end up with a file of around 800MB, no matter how low it set the bit rate or how much noise reduction or temporal smoothing (tools to make individual frames smaller) I do.

As an extreme example, I recorded a 2-hour and 1 minute MPEG1 sample of the blue screen my VCR shows when it has no other input - quite possibly the easiest thing I could possibly record. No audio at all. I encoded the MPEG using virtualdub on a couple of different machines using Divx5 Pro using different size-reduction techniques and a very reasonable 250kb/s bit-rate.
By my calculations, the file should've been about 225MB.

The smallest result I got was 760-something megs.

Anyone else run into this or anything like it?

I found a file I did a while ago that was a VHS capture that I set to 320x240 and a low bit-rate. It's 101 minutes long, and comes to 653MB (which works out to 783 for 2 hours). Unfortunately, I don't remember the exact settings I used, the filters applied, or even if it was 1 or 2-pass. If you give me a couple of days, I'll try a couple of different settings for low bit-rate encodes, and see if I come up with the same results (I have some old tapes I've been meaning to do anyway). Does the file size floor only show up on files over 2 hours?
 

Mercutio

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Looks like fiddling with the quantizer settings will resolve the immediate issue, but it doesn't explain why I'm having to do this with divx5 when earlier versions happily made predicatably small files at low bit rates.

2 hours seems to be the starting point for unpredictability.
 

SteveC

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Merc., what are the exact setting you are(were) using. I was unable to reproduce you're results. I tried a 2 hour 9 minute capture of you're blue screen test and used Vdub to set up a bunch of encodes in batch mode before I went to sleep last night. I used a setting of 250kb/s for all, and adjusted various other settings, including the quantizer, and no filters were applied to any of them. They all came to about 230MB, give or take a few megs.
 

SteveC

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SteveC said:
Merc., what are the exact setting you are(were) using. I was unable to reproduce you're results.
Ugh. There should be a question mark after the first sentence, and "you're" should be "your". I suck at spelling and grammar.
 

Mercutio

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Fresh installed a fairly vanilla PC. XP1800 + 256MB PC2100 + Epox 8KHAL+ and Win2000. Installed Vdub 1.4.7. Installed divx pro 5.0.2.

I'm encoding a 2 hour and one minute MPEG1 of a blue screen. No audio.
Compression is set to a paltry 400kbps, default quantizers (min 2 max 12), no GBC, bidirectional encoding or quarter pel. Frame size is 640x480. There is no static or any change in the image in the 2-hour period. Solid blue. I'm using the deinterlacer builtin to Divx5. I don't have any an vdub filters on (normally, I'd be using at least a couple).

Half-hour into the encoding process I've got a predicted file size of 806MB and I'm sailing along at 22fps. The frame sizes appear to be unusually jagged considering what I'm encoding and sometimes spike up to 20k.

Apparently I live in the divx twilight zone.
 

SteveC

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The only differences are I'm using Vdub 1.4.13 and not using Divx's deinterlacing. I suspect the latter may be the culprit, as I don't remember having any difficulty with earlier versions of Vdub, and I've never used Divx's deinterlacing.
 

Mercutio

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Futzed around for a couple more weekends with Divx 5.02, but I never got results that were appreciably better than before.

Downloaded divx 5.03, noticed some minor UI changes in the control interface (no more minimum/maximum quantizers, and now there are usage profile which... do something, I guess) , but amazingly, in the short time I've had it, I've found filesizes to be predictable again. My "example" file from above comes out to a rational 240MB with the default settings and same bitrate.

In short, I have no idea what was wrong before, but divx 5.03 seems to have fixed it.

Also, as seen on /., there's an article on THG about a divx;) home theater component.
 

blakerwry

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that sucks.. i liked the min/max quantizers... sometimes the quality level was much better quality in certain movies if i could adjust this by hand.....


oh well... I'll give 5.03 a go and see if it works any better
 
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