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  1. Normally when a bitrate calculator is used it assumes that the video is full D1 resolution. In theory I should be able to use half D1 and half the bitrate, right?

    Is there a calculator that also asks for the input and/or output resolution?
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  2. Bitrate is completely independent of resolution. It's only a function of filesize and length of video. The answer to your question is no, since resolution has nothing to do with it.
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  3. Member
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    Originally Posted by manono
    Bitrate is completely independent of resolution. It's only a function of filesize and length of video. The answer to your question is no, since resolution has nothing to do with it.
    But if it's a function of filesize and length of video, then resolution DOES matter -- changing resolution and maintaining the same bitrate DOES result in a different filesize, so the question IS a valid one.

    I can fit more video on a DVD when I scale back the resolution to half-D1 (352x480), which works fine for DISH Network PVR captures (native capture resolution for DISH Network PVR and TiVo captures is 480x480, so scaling up to full-D1 resolution doesn't gain me anything, while scaling DOWN to half-D1 doesn't lose much, and allows me to put more on a DVD).

    Sounds to me like FitCD is what stantheman1976 is looking for:

    http://www.videohelp.com/tools?tool=FitCD
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  4. Originally Posted by jbodin
    changing resolution and maintaining the same bitrate DOES result in a different filesize
    No it doesn't. I suspect you meant "maintaining the same image quality".
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  5. Member
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    Originally Posted by jagabo
    Originally Posted by jbodin
    changing resolution and maintaining the same bitrate DOES result in a different filesize
    No it doesn't. I suspect you meant "maintaining the same image quality".
    I think were essentially saying the same thing. By lowering my resolution I'm actually lowering the image quality somewhat. Since changing the resolution lowers the image quality (by changing the number of pixels per frame), my file size gets smaller even if I maintain the original bitrate (less pixels to move for the entire production using a given bitrate).

    http://www.doom9.org/index.html?/bitrate_guide.htm
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  6. Video Restorer lordsmurf's Avatar
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    No, you're wrong.

    Resolution determines depth of detail. Of course, source has to have the same detail.

    Bitrate determines filesize.

    The allocation of bitrate to resolution determines image quality.

    Resolution and image quality have zero bearing on filesize.
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  7. Originally Posted by jbodin
    Since changing the resolution lowers the image quality (by changing the number of pixels per frame), my file size gets smaller even if I maintain the original bitrate (less pixels to move for the entire production using a given bitrate).
    No. File size = bitrate * running time. Period. If your encoder isn't giving the same file size for a 720x480 and 352x480 frame at the same bitrate it is not delivering the bitrate you requested.
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    Huh. Interesting stuff, guys -- I'm going to have to look at what I've been doing lately to figure out what's going on. I've been using gui4ffmpeg to do some conversions for me, and using a given bitrate (5000), I find that the output file size varies depending on the resolution selected. I've been using this to convert video captures from my DISH Network PVR to half-D1 resolution DVD-compliant MPEG files.

    Weird. Thanks for setting me straight on this -- now I've just got to figure out why I get different file sizes based on the selected resolution when I've been doing the conversions.
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    the only other variables I can think of are:
    1. whether or not you are using constant or variable bitrate.
    2. If the audio format/bitrate is different between the videos.
    3. The program is going behind your back and changing things for you.
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  10. Member
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    Thanks for the heads-up on this, guys -- I think I figured out what's going on . . . this is from the gui4ffmpeg help file:

    What's happend if the video bitrate was decreased but
    quality and file size are unchanged?
    If the source file contains not so much information (cartoon,
    low motion, ...), the selected bitrate will not reached. Have a
    look in ffmpeg's DOS box at the actual bitrate while encoding.
    I have noticed that the indicated bitrate in ffmpeg's DOS box doesn't reflect the selected bitrate that I've been dialing-in, so apparently the capture files I've been dealing with are low-information (and presumably lower bitrate) files.

    Good to know. Thanks!

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  11. Originally Posted by jbodin
    I have noticed that the indicated bitrate in ffmpeg's DOS box doesn't reflect the selected bitrate that I've been dialing-in, so apparently the capture files I've been dealing with are low-information (and presumably lower bitrate) files.
    I don't know ffmpeg but many MPEG encoders have minimum/maximum quantizer settings. If the min quantizer is too high the codec sometimes can't generate high enough a bitrate. If you want to fill up a DVD (and get that little bit higher quality) you can reduce the min quantizer.
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  12. I have noticed that the indicated bitrate in ffmpeg's DOS box doesn't reflect the selected bitrate that I've been dialing-in...

    It's called saturating the codec. It's using all the bits it can for the source and the settings you have. It's giving you the best quality it can for your settings. It's also an indication (in my opinion) that you're setting it up wrong, as you could have used a smaller file size, a larger resolution, a better quantization matrix, a good AviSynth sharpener, or made some other changes, and still have had virtually the same (or even better) quality.
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  13. Member
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    Originally Posted by jagabo
    Originally Posted by jbodin
    Since changing the resolution lowers the image quality (by changing the number of pixels per frame), my file size gets smaller even if I maintain the original bitrate (less pixels to move for the entire production using a given bitrate).
    No. File size = bitrate * running time. Period. If your encoder isn't giving the same file size for a 720x480 and 352x480 frame at the same bitrate it is not delivering the bitrate you requested.
    Found this tidbit here:

    http://www.videohelp.com/forum/archive/t300220.html

    Originally Posted by daamon
    An encode at full-D1 will require a minimum bitrate before you start noticing quality loss. By reducing the resolution to half-D1, in theory, you'll need around roughly half the bitrate before you start noticing a similar quality loss. The point at which this happens is subjective and so can't be calculated.

    However, because you have a lower resolution you don't need as high a bitrate to get a decent (acceptable to you) picture - this is where the smaller filesize comes in from using the lower bitrate.
    This explains why my filesizes are smaller when using a half-D1 resolution (352x480) instead of a full-D1 resolution (720x480); the lower resolution simply doesn't require the higher bitrate. Is this what you mean by "saturating the codec," manono?
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  14. Originally Posted by jbodin
    This explains why my filesizes are smaller when using a half-D1 resolution (352x480) instead of a full-D1 resolution (720x480); the lower resolution simply doesn't require the higher bitrate. Is this what you mean by "saturating the codec," manono?
    Yes, that is what he meant. But be aware that other MPEG encoders might not make the same decision about now much bitrate that particular video really needs.
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