BitRate Calculators

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BitRate Calculators

Postby Bushido Philosopher » Wed Dec 04, 2002 1:35 am

Going through a lot of bitrate calculators, I couldn't help but notice that there are none which can input a frame size (.e. 720x480, 512x272).

Do I just not worry about that or is there some way that I can figure this out?
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Postby Zarxrax » Wed Dec 04, 2002 1:49 am

The resolution has nothing to do with the final filesize.
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Postby TokyoU15 » Wed Dec 04, 2002 2:55 pm

Yes it does...Bigger resolution=bigger file size. Smaller res.= smaller file size.

At least that was my experience with XviD.
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Postby Zarxrax » Wed Dec 04, 2002 3:40 pm

The ONLY thing that determines filesize is bitrate. Resolution does not effect the filesize. If resolution effected the filesize in any way whatsoever, then the shear notion of such a thing as "bitrate" would be utterly pointless.
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Postby trythil » Wed Dec 04, 2002 3:58 pm

Zarxrax wrote:The ONLY thing that determines filesize is bitrate. Resolution does not effect the filesize. If resolution effected the filesize in any way whatsoever, then the shear notion of such a thing as "bitrate" would be utterly pointless.


Higher resolution = more pixels to encode = more data = bigger filesize.

Code: Select all
sh-2.05a$ ls -l *.avi
-rw-r--r--    1 trythil  users      503574 Dec  4 16:02 preview.360.avi
-rw-r--r--    1 trythil  users     1190594 Dec  4 16:02 preview.720.avi
-rw-r--r--    1 trythil  users      970276 Dec  2 21:38 preview.avi
-rw-r--r--    1 trythil  users     1861524 Nov 16 03:29 preview2.avi

sh-2.05a$ tcprobe -i preview.360.avi
[tcprobe] RIFF data, AVI video
[avilib] V: 29.970 fps, codec=DIVX, frames=281, width=360, height=240
[tcprobe] summary for preview.360.avi, (*) = not default, 0 = not detected
import frame size: -g 360x240 [720x576] (*)
       frame rate: -f 29.970 [25.000] frc=4 (*)
   no audio track: use "null" import module for audio
           length: 281 frames, frame_time=33 msec

sh-2.05a$ tcprobe -i preview.720.avi
[tcprobe] RIFF data, AVI video
[avilib] V: 29.970 fps, codec=DIVX, frames=281, width=720, height=480
[tcprobe] summary for preview.720.avi, (*) = not default, 0 = not detected
import frame size: -g 720x480 [720x576] (*)
       frame rate: -f 29.970 [25.000] frc=4 (*)
   no audio track: use "null" import module for audio
           length: 281 frames, frame_time=33 msec
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Postby trythil » Wed Dec 04, 2002 4:00 pm

Doh. I should also note that both preview.360.avi and preview.720.avi were encoded at 1000 kbps CBR.
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Postby RadicalEd0 » Wed Dec 04, 2002 4:15 pm

resolution only plays a part in the output size when a quantizer or quality is set, not bitrate. For caluclation, I'd like to say there is a direct relationship between a resolution like 640x480 and 1/4th that of 320x240, but there just isnt in the world of lossy compression. An image might be 4 times as large but also be 2 times as compressible, requiring only 2x the bitrate for the same quality.
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Postby klinky » Wed Dec 04, 2002 7:03 pm

RadicalEd0 wrote:resolution only plays a part in the output size when a quantizer or quality is set, not bitrate. For caluclation, I'd like to say there is a direct relationship between a resolution like 640x480 and 1/4th that of 320x240, but there just isnt in the world of lossy compression. An image might be 4 times as large but also be 2 times as compressible, requiring only 2x the bitrate for the same quality.


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Postby Bushido Philosopher » Thu Dec 05, 2002 12:36 am

so.......answer to my question please? :lol:
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Postby klinky » Thu Dec 05, 2002 12:51 am

Ko Oh Yoku wrote:so.......answer to my question please? :lol:



Err, there is no answer because there are no bitrate calcs because it doesn't matter what resolution you use.

Bitrate calc is what you use if you want to get something to a specific size. So it's going to tell you a bitrate that does not change with resolution.

If your video is 640x480 and you want it to fit into 50MB, it will give you the same results as a 320x240 video you want to fit into 50MB, just the 50MB will use more bits per frame. Resolution doesn't play a part in the final file size unless you use quality based encoding, which you cannot predict.

So, there is no bitrate calc that factors resolution, because it plays no part when you want to calculate a bitrate for a predetermined size.

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Postby klinky » Thu Dec 05, 2002 12:53 am

god damnit... >_<


...there are no bitrate calcs that factor the resolution...

...a 320x240 video will take the same amount of bits in a 50MB file as a 640x480 video would.

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