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  1. Hi guys,

    I am trying to make a 700 MB backup from a file with big size and excellent quality.

    The source file is: 5.50 GB, 1h 49m, 5657 Kbps, 1280x534, 23.976, 0.345 bits per pixel, audio 1510 Kbps, 48 KHz

    Backup file 1 is: 640x268, 700 MB, 750 Kbps, 0.182 bits per pixel, audio 128 Kbps, 48 KHz
    Backup file 2 is: 672x280, 700 MB, 750 Kbps, 0.166 bits per pixel, audio 128 Kbps, 48 KHz
    Backup file 3 is: 768x320, 700 MB, 750 Kbps, 0.127 bits per pixel, audio 128 Kbps, 48 KHz

    All backup files are same, except they have different resolution and different bits per pixel.

    I wanted to hear your opinion, do you guys think that increasing the resolution and decreasing the bits per pixel will look better? Or vice versa?
    Should I go for the file with higher resolution or the file with higher bits per pixel? Which of the 3 backup files would you choose?

    Thanks for your time.
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  2. Originally Posted by pavlekocev25 View Post
    do you guys think that increasing the resolution and decreasing the bits per pixel will look better?
    Depends on the particular video.
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  3. if a video/movie are mostly "talking heads", it is not that bitrate demanding so it would be better to use higher resolution. But you add some constant action to it and smaller resolution might feel better. But anyway, your differences in resolution is not that big, not sure if you would register the differences much at all.
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  4. You should go with the one that looks better to you.

    BTW, bits-per-pixel is not a measure of quality. Actually, it shows nothing.
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  5. Member
    Join Date
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    Technically those are not backups
    technically a backup contains ALL the Data of the original

    you are making reduced resolution/quality copies
    what is the purpose of the reduced copy ?
    to played on portable media ?
    or to backup the main file if lost or corrupted
    in the first case OK, what ever pleases your eye
    If the second case you have failed terribly
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  6. Thanks guys.

    In this case, when converting a video file to a fixed size, like 700 MB for example, at first I thought that there could be some formula including the target size, resolution, pixels, Kbps and all those things, and before you make the conversion you can make your calculation and find out the magic number of what resolution to use, and end up with the perfect resolution for your video.

    What I was hoping for was some way to calculate everything, so you can end up with the perfect resolution on the first try, and convert the file only 1 time, so that you don't need to make more conversions of the same file.

    But, I guess in this case it can never be perfect on the first try because every video is different, every video source file is different (some better quality and some average quality) and every video has a variable amount of fast moving action scenes and slow moving static scenes.

    So I guess every time when we do this type of conversion it can never be perfect on the first try, and we need to make more conversions of the same file with different resolutions, and then compare more output files with different resolutions and see which one looks best.

    @theewizard: Yes, I wanted to convert some of my DVDs to a smaller size, of 700 MB for example, and play them on a portable video player.

    Anyway, thanks again guys, I realize now that it really depends on the type of video, and that I need to convert the same video file more times when I do this kind of thing, but if you have any small tips and hints, that could help me save some time and make only 2-3 conversions of the same file instead of 5, they are more than welcome.
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  7. Member
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    actually this easy to answer
    don't convert too so small a size

    how many MB/GB is the memory

    if you convert at roughly 700mb per HOUR a 90min movie is just over 1gig, a 2hr movie is 1.4gig
    a 16gb SD card will hold 20hrs, (10) 2hr movies
    just how many movies are you trying to put on this portable player
    640-720 * 400-480 with a target size of 1400mb
    will work quite well for most players/tablets with a screen large enough to actully enjoy like 7" or larger
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  8. Originally Posted by pavlekocev25 View Post
    But, I guess in this case it can never be perfect on the first try because every video is different, every video source file is different (some better quality and some average quality) and every video has a variable amount of fast moving action scenes and slow moving static scenes.
    That is correct. Some programs (AutoGK for example) encode several short sections spread throughout the file to get an idea what the file is like, then decide on what frame size to use to deliver reasonable quality when encoding the entire video at the requested file size. But it's always possible that the samples just happen to hit sections that aren't really representative of the entire video. And keep in mind that when you do this you are trading away resolution in order to get fewer artifacts.
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  9. It's 8 GB Card, and I wanted to put around 10 movies on it, so I'll see what I can do, thanks again everyone.
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  10. Originally Posted by _Al_ View Post
    if a video/movie are mostly "talking heads", it is not that bitrate demanding so it would be better to use higher resolution. But you add some constant action to it and smaller resolution might feel better. But anyway, your differences in resolution is not that big, not sure if you would register the differences much at all.
    Be careful, where there is less action, loss is also less tolerable since you will be focusing and noticing more details, or the loss thereof. It's a common misconception but action movies are actually easier to compress than ones with little movement because loss in fast-moving scenes is less important than loss you will be continually staring at for half-minute stretches.

    Predicting which content needs more bitrate is a lot trickier than you think.

    Thanks guys.

    In this case, when converting a video file to a fixed size, like 700 MB for example, at first I thought that there could be some formula including the target size, resolution, pixels, Kbps and all those things, and before you make the conversion you can make your calculation and find out the magic number of what resolution to use, and end up with the perfect resolution for your video.

    What I was hoping for was some way to calculate everything, so you can end up with the perfect resolution on the first try, and convert the file only 1 time, so that you don't need to make more conversions of the same file.

    But, I guess in this case it can never be perfect on the first try because every video is different, every video source file is different (some better quality and some average quality) and every video has a variable amount of fast moving action scenes and slow moving static scenes.
    This takes experience and intuition. I do 700MB rips from DVDs and Blu-rays all the time, I've been doing it for almost a decade and I still lack proper judgment in this respect. My friend on the other hand who is also an encoder has a talent for predicting exactly what resolution or bitrate to use.
    You need to watch the whole video and judge the rough complexity and thus how much you need to adjust the bitrate or resolution if you're using a fixed size.
    But as highlighted above, it can be misleading especially since what encoders perceive as complex won't always correlate to human perception.

    A big thing to look out for is noise, rain or snow. High-frequency details are the biggest bandwidth killer. Any movie with lots of rainy scenes like Jurassic Park are examples. Anything with "swarms" in it like zombie movies rich with scenes of thousands of zombies flocking.
    Those will be twice as complex as the average video. If the average video needs 0.100 BPP, the aforementioned will need 0.200 BPP for the same quality or more.

    If you wanna store 700MB movies on anything, buy a 64GB USB stick, they're only like $20 now.
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