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  1. Hi all, I have checked Youtube Recommended setting and it wants closed GOP with its half the frame rate. I don't know what that really means, but Handbrake does seem to have that setting. Can anyone explain clearly what GOP means and if there is a way to get closed GOP with its half the frame rate using handbrake? I render as 720P high frame rate.
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    Search Comp PM
    https://en.wikipedia.org/wiki/Group_of_pictures

    It's really the main thing that allows such levels of compression.
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  3. Each frame in a closed GOP only references other frames within the GOP. In open GOPs the last few frames of the GOP may reference the keyframe of the next GOP.
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  4. Does Handbrake allow me to encode as closed GOP with half of its frame rate?
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  5. Handbrake doesn't give you GUI control of GOP size or whether they are open or closed. But the default in its x264 encoder is closed GOP so you probably don't need to worry about that one. To specify a maximum GOP size you can enter it in the x264 Extra Options box. For example if your frame rate is 60 fps and you want half second GOPs enter "keyint=30" (without the quotes). If you need to specify more than one extra option separate the options with a colon. So if you wanted to specify GOP size 30 and open GOPs enter "keyint=30:open-gop" (again, without the quotes).

    The default in x265 is open GOPs. If you want closed GOPs you have to enter "no-open-gop" in the Extra Options box. GOP size is specified the same was as in x264, "keyint=30".

    See the x264 and x265 docs for any other options you may need to specify that way.
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  6. Originally Posted by jagabo View Post
    Each frame in a closed GOP only references other frames within the GOP. In open GOPs the last few frames of the GOP may reference the keyframe of the next GOP.
    ok for better video quality which is better open or closed?
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  7. Originally Posted by Takashi View Post
    Originally Posted by jagabo View Post
    Each frame in a closed GOP only references other frames within the GOP. In open GOPs the last few frames of the GOP may reference the keyframe of the next GOP.
    ok for better video quality which is better open or closed?
    Open. But unless you're using very short GOPs the difference is negligible.
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  8. Originally Posted by jagabo View Post
    Originally Posted by Takashi View Post
    Originally Posted by jagabo View Post
    Each frame in a closed GOP only references other frames within the GOP. In open GOPs the last few frames of the GOP may reference the keyframe of the next GOP.
    ok for better video quality which is better open or closed?
    Open. But unless you're using very short GOPs the difference is negligible.
    you mean --keyint and --min-keyint?
    use --keyint 300 --min-keyint 30 for NTSC
    Last edited by Takashi; 26th Sep 2020 at 22:11.
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  9. Yes, keyint is the GOP size. So" --keyint 300" creates 300 (max) frame GOPs. The default in x264 is closed GOPs. The default in x264 is also to start a new GOP at scene changes. Some many GOPs will be less than 300. "--min-keyint 30" prevents the GOPs from being less than 30 (to prevent bitrate spikes from too many I frames).

    If your source is 720p at 50 fps youtube's recommendation of "closed GOP with its half the frame rate" means set --keyint 25. The min-keyint recommendation of 1/10 keyint becomes silly with such small GOPs. I'd set it to maybe 1/2 keyint, --min-keyint 12.

    Note that "--keyint 25 --min-keyint 12" is the format for the x264 command line encoder. In Handbrake you need to use Handbrake's syntax "keyint=25:min-keyint=12" in the Extra Options box.
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  10. Originally Posted by jagabo View Post
    Yes, keyint is the GOP size. So" --keyint 300" creates 300 (max) frame GOPs. The default in x264 is closed GOPs. The default in x264 is also to start a new GOP at scene changes. Some many GOPs will be less than 300. "--min-keyint 30" prevents the GOPs from being less than 30 (to prevent bitrate spikes from too many I frames).

    If your source is 720p at 50 fps youtube's recommendation of "closed GOP with its half the frame rate" means set --keyint 25. The min-keyint recommendation of 1/10 keyint becomes silly with such small GOPs. I'd set it to maybe 1/2 keyint, --min-keyint 12.

    Note that "--keyint 25 --min-keyint 12" is the format for the x264 command line encoder. In Handbrake you need to use Handbrake's syntax "keyint=25:min-keyint=12" in the Extra Options box.
    for youtube I use filmora and it's fine
    but now I use MeGUI to make backup copies of my DVD collection to MP4 some are PAL and others NTSC

    so. Do you think "--keyint 25 --min-keyint 12" is ok for DVD PAL? or would it be better to go with "--keyint 250 --min-keyint 25"?

    And what do you advise me for NTSC DVDs?
    "--keyint 300 --min-keyint 30" "or --keyint 30 --min-keyint 15"

    and finally which is better for GOP Calculation Fixed or FPS based?
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  11. From some downloaded youtube video, they seem to be using 5s keyframes.

    Recommandations are just that, recommandations. They reencode your video in any case.
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  12. Originally Posted by butterw View Post
    From some downloaded youtube video, they seem to be using 5s keyframes.

    Recommandations are just that, recommandations. They reencode your video in any case.
    and it's not like youtube has the best encoder in the world hahaha!
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  13. Originally Posted by Takashi View Post
    but now I use MeGUI to make backup copies of my DVD collection to MP4 some are PAL and others NTSC

    so. Do you think "--keyint 25 --min-keyint 12" is ok for DVD PAL? or would it be better to go with "--keyint 250 --min-keyint 25"?

    And what do you advise me for NTSC DVDs?
    "--keyint 300 --min-keyint 30" "or --keyint 30 --min-keyint 15"
    Just leave the keyint at the default -- 250 frames.

    Originally Posted by Takashi View Post
    and finally which is better for GOP Calculation Fixed or FPS based?
    In theory, the longer the GOP the lower the bitrate requirement. But once you get beyond 50 or so there's not much difference with most material. The default is fine for most video. Worrying about whether it should be 250 or 300 is ridiculous. Unless you have specific requirements. For example, Blu-ray is limited to 2 second GOPs (50 frames at 25 fps), if I remember correctly.

    You can easily run experiments to test this yourself. Do CRF encodings with 10, 50, 100, 250, and 500 frame GOPs and compare the resulting file sizes.
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  14. Originally Posted by jagabo View Post
    Originally Posted by Takashi View Post
    but now I use MeGUI to make backup copies of my DVD collection to MP4 some are PAL and others NTSC

    so. Do you think "--keyint 25 --min-keyint 12" is ok for DVD PAL? or would it be better to go with "--keyint 250 --min-keyint 25"?

    And what do you advise me for NTSC DVDs?
    "--keyint 300 --min-keyint 30" "or --keyint 30 --min-keyint 15"
    Just leave the keyint at the default -- 250 frames.

    Originally Posted by Takashi View Post
    and finally which is better for GOP Calculation Fixed or FPS based?
    In theory, the longer the GOP the lower the bitrate requirement. But once you get beyond 50 or so there's not much difference with most material. The default is fine for most video. Worrying about whether it should be 250 or 300 is ridiculous. Unless you have specific requirements. For example, Blu-ray is limited to 2 second GOPs (50 frames at 25 fps), if I remember correctly.

    You can easily run experiments to test this yourself. Do CRF encodings with 10, 50, 100, 250, and 500 frame GOPs and compare the resulting file sizes.
    ok thank you very much jagabo
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