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  1. Member
    Join Date: Feb 2014
    Location: Canada
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    Hello all,

    I am newbie in the video domain. Despite that fact, there is a question that has been gnawing at me for some time, so here goes:
    How can several movie files (3 files to be precise) depicting the EXACT same movie, having the same video codec, video resolution (i.e. X*Y pixels) and frame per second rate, all be of various sizes. Not different sizes that vary by <10%, but different sizes where the largest file is more than 2 times greater than the smallest. Also, all movies files have the same duration to the ~second. However when the files are viewed, I do not see any visible differences.
    I would have expected that a movie file size would be mostly dependent on the fps, video res, video codec and duration. I do not know anything about movie compression (if there is such a thing) but the term video codec implies for me that the movie would have some sort of compression - somewhat akin to a bitmap vs a jpeg. However, if the movie files all depict the same movie, I would expect that all the 3 files would be of similar sizes. This is not the case as I explained earlier. How is this possible?

    Thanks
    -Bob
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  2. original is very important, if you have different sources you get different results , like DVD vs. BD source,

    all videos could be H.264 but obtained by different encoder,for example, x264 vs. MainConcept and even settings could be different within same encoder,

    and also some encodings could have filters applied before encoding, like denoise, but some not
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  3. Member
    Join Date: Mar 2008
    Location: United States
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    Actually the BMP Vs. JPG is not a bad analogy. Just as the JPG can be encoded with various levels of quality,
    so can the movie using the lossy codec.
    Can you hear the difference between a 160 kbps mp3 and a 320 kbps mp3?
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  4. Code:
    file size = bitrate * running time
    So twice the bitrate means twice the size. Whether you can see a difference or not depends on how closely you look and whether or not you know what to look for.
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  5. Member
    Join Date: Jul 2007
    Location: United States
    Search Comp PM
    Originally Posted by jagabo View Post
    Code:
    file size = bitrate * running time
    So twice the bitrate means twice the size. Whether you can see a difference or not depends on how closely you look and whether or not you know what to look for.
    +1 on jagabo's post.

    On another thread, a poster is rambling on about how DVD quality is "amazing" and Blu-Ray quality is largely unnecessary. Just because you can't see a difference doesn't mean there isn't any. I have some movies on videotape, Laserdisc, DVD and Blu-Ray and can tell definitely tell the differences between each version.

    Sorry for repeating myself, but I used to wonder what all the hoopla about "black levels" was about until I watched a horror film that had a lot of dark scenes. It took me a while for for it to dawn on me that I was seeing details that I would never have been able to see if the video bitrate was halved.
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  6. Member
    Join Date: Jul 2007
    Location: United States
    Search Comp PM
    Watch Brain Games or Your Bleeped Up Brain to see how easy is to 'not see' things that you aren't previously weren't aware of.
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  7. Also keep in mind that some video is more compressible than others. A movie shot on high grain film with lots of action will require much more bitrate than a movie with little grain and little motion.
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