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Old October 24th, 2008, 06:05 PM   #1
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WMV render almost twice as big?

Hi all,

I have 2 seperate projects shot with an SR12 that I rendered to 852x480 SD in wmv format. Afaik I rendered with the same settings of quality VBR at 90%. The video bitrate for the former project is listed as 967 kbps and 1602 kbps for the latter, resulting in a much bigger file size. I find the quality fine for the former project. I'm curious to know why there's so much difference, and what should I do about it to get the file size down? What settings do you use when rendering with wmv?

Thanks,

David H.
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Old October 25th, 2008, 04:27 AM   #2
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David

Presuming all settings are the same then I would guess there is a lot more movement/detail etc in the larger clip. It doesn't have to be 'real' movement - it could be picture noise, if for instance you've used a high amount of gain etc. So the encoder has to user more bits per second to record that movement.

I've just encoded 2 WMVs - each of a minute duration at 720x576 at Quality VBR of 90%. The first one (interviews - not much happening) was 7MB with a bit reat of 911kbps. The second one (wedding dance - dark, lots of movement) was 16MB with a bit rate of 2258kbps.

By the way encoding that second clip at 83% quality (what I normally use) dropped the file size to just over 9MB! Most people wouldn't notice the difference between that and the 90% version.

Ian
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Old October 26th, 2008, 12:14 AM   #3
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Hi Ian,

Thanks so much for the info. I'm giving 83% a shot!

Cheers,

David H.
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Old October 26th, 2008, 12:25 AM   #4
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Could you please explain how or why you chose 852x480? SD is 720x480. You are rendering a much larger frame size than necessary. This will make larger files.

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Originally Posted by David Horwitz View Post
Hi all,

I have 2 seperate projects shot with an SR12 that I rendered to 852x480 SD in wmv format.
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Old October 27th, 2008, 11:21 PM   #5
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Hi Perrone,

Yes, I shot in 1920x1080 HD, and so that is the setting I chose to keep the aspect ratio the same. Is that not the appropriate setting? It looks good when I upload to blip.tv

Cheers,

David H.
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Old October 27th, 2008, 11:36 PM   #6
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Generally, it's advantageous to render to multiples. So you might want to reduce the size by a factor of 2 or a factor of 4. 960x540 requires integer math by the compression algorithm. You are forcing some pretty heavy calculations per frame with your choices, and making things an awful lot harder than need be. I'd be interested to know what happens if you render at 960x540 at the same bitrate, and see how long it takes, and what the results are.

Some codecs won't even render unless the frame sizes are divisible by four or by eight. So be aware.
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Old October 28th, 2008, 12:05 AM   #7
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Thanks for the info Perrone, I'll give it a shot!

Cheers,

D
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