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  1. So I have many 1080p video files. Their size varies between 6.7GB and 8.5GB.
    I'm trying to reduce that size to around 4.5GB, I used Handbrake with the H264 codec and I reduced a 6.8GB video file to 4.6GB.
    My question is, is that too much? And how can I detect if there is a consequent loss in quality?
    When viewing the video it looks about the same but I'm not sure, is there any software that can take a screenshot of the movie at the exact defined moment? When I mean exact, I really mean exact, the exact same frame.
    Thanks.
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  2. Mod Neophyte Super Moderator redwudz's Avatar
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    If you can open the video in AVIDemux or VirtualDub, you can move to a frame number and take a snapshot, but I'm not sure that will tell you much. And make sure it's on a keyframe, especially with highly compressed codecs like H.264. The quality at a particular size/bitrate depends on the video you are encoding. More action, more bright/dark areas, more video noise, the more likely it will need a higher bitrate to keep the quality. Static scene, low contrast videos generally need less bitrate.

    If you don't need an exact output size, you would probably be better off using constant quality encode instead of target size, if quality is your main concern. Try using the preset CQ and see how it looks. You won't have a lot of control over the output size, but they may average out to the size you want. I use 19.5 CQ as a compromise and at least with SD videos, I can't tell a difference. This is to reduce a 8GB DVD to about 2GB.

    And welcome to our forums.
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  3. Thanks.
    So I opened them with AVIDemux and took a screenshot. There's not much difference but the smaller one is only a little more blurry and there's less grain (it's an old movie).
    I'm trying the CQ preset, could you tell me how am I supposed to know which value to put? Are those levels of quality?
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  4. Much depends on how you're viewing them, how large the TV, how close you sit. I've found with a 47" HDTV, compressing down to BD5 for a 90 minute movie is watchable.

    Someone here said (maybe Lord Smurf) that H,264 degrades "gracefully", meaning you can compress the snot out of it without obvious macroblocking, like you get with MPEG2. I've found that to be true.

    However, you *are* losing video quality the more it get re-compressed (re-encoded). And when it reaches a certain point, it's no longer degrading gracefully, it gets real ugly, quickly. I'd say absolute minimum for re-encoding a good clean commercial movie is 4,500 kps. Encoding using CQ, as Redwudz suggests, is a better way to go about it than by target size.

    Good luck.
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  5. I tried 4500kbps and the file is even smaller (3.3GB). As for the quality it seems to be pretty comfortable seen from a 22.5".
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  6. Member edDV's Avatar
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    The problems first show with motion artifacts so stills don't tell you much.

    The trade issue is resolution vs compression artifacts that mostly show during motion.

    Blue-Ray 1920x1080 24p h.264 runs 16-25 Mb/s for a reason (acceptable quality on an large screen HD display). It is far from pro master quality but carefully crafted for Blu-Ray home viewing.

    If you want to compress more, then display size/viewing distance and source characteristics affect optimal encode.

    For source, the more motion, dark scenes or noise, the more you favor bit rate over resolution. For "X-Men" or "Fast and Furious" you would drop resolution (1280x720p or 960x540p) faster than you would lower bit rate.

    For static travel videos or simple fixed camera dramas, you can get away with more compression.

    For screens under 36 inches, you will see little difference between 1920x1080p and 1280x70p unless you are watching from sub 20 inches. Only exceptions would be movies with fine text which are rare.

    On average, any HD h.264 under 8 Mb/s will see serious decline in quality.
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  7. In my experience using h.264 the loss of quality will be more so in the loss of detail... not so much noise and artifacting. Noticing loss in detail is alot harder especially if you don't know where the loss is happening. Anything less than 5000kbp is usually unacceptable for 1080p. You might want to consider re-encoding to 720p, especially if viewing on a smaller tv. You won't notice the difference between 1080p and 720p unless your looking right at the tv from a foot away, and is bigger than 40inches.
    Last edited by souper; 19th Jul 2011 at 21:32.
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  8. Member edDV's Avatar
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    Originally Posted by souper View Post
    In my experience using h.264 the loss of quality will be more so in the loss of detail... not so much noise and artifacting. Noticing loss in detail is alot harder especially if you don't know where the loss is happening. Anything less than 5000kbp is usually unacceptable for 1080p. You might want to consider re-encoding to 720p, especially if viewing on a smaller tv. You won't notice the difference between 1080p and 720p unless your looking right at the tv from a foot away, and is bigger than 40inches.
    I think we are on a similar track but loss of low motion detail is about resolution but high compression creates motion artifacts. Noise refers to source noise. If the source has noise you need more bit rate.

    I disagree that 5000 kbps is adequate for 1080 24p. May be adequate for 720 24p. Everyone has a crap threshold and the current display may not show the difference. But in the future when you play this on a quality large screen you will need to capture again.
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  9. Mod Neophyte Super Moderator redwudz's Avatar
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    I'm trying the CQ preset, could you tell me how am I supposed to know which value to put? Are those levels of quality?
    With H.264 encoding in Handbrake, the smaller the CQ number, the higher the quality. (And the larger the file size.) The default, 20, is a good place to start. If the file is too big, try raising the CQ up a little. You can make up a short test clip and use that with different CQ settings. Then you can likely see the quality difference and filesize difference.
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