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  1. Member
    Join Date: Jan 2010
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    I am using a Sony RX100M2 for video at 50p 28Mbps.

    I want to convert some clips to 25p, but the methods I've been looking at seem to just drop every second frame, which seems to me a rather crude way of doing is as it's simply throwing away half your data. Also, the optimum shutter speed for 50p is 1/100 sec, so if you're discarding every second frame the resulting video at 25p won't look very smooth in panning.


    Is there a way to convert 50p to 25p that makes use of all the data/frames to ensure smooth and high quality playback?
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  2. Member racer-x's Avatar
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    Sure....................but it will then play at 50% of original speed.
    The memories of a man in his old age, are the deeds of the man in his prime.......
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  3. Member
    Join Date: Sep 2007
    Location: Canada
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    Not really

    There are pros/cons to each method you choose. You simply cannot reduce 1/2 the frames without losing something

    Some options are

    1) straight decimation , but add motion blur (e.g. mvtools, mflowblur...)

    2) some combination of frame blending

    e.g.
    merge(selectodd, selecteven)
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  4. You could blend the frames, but you won't like the result.

    Using AviSynth's QTGMC you can add some motion blur to smooth those pans. It's about the best way I know to do it.

    Something like:

    SelectEven()
    QTGMC( Preset="Slower", FPSDivisor=2, ShutterBlur=1, ShutterAngleSrc=30, ShutterAngleOut=180 )

    should do it. The settings are adjustable. From the included doc:

    Single-rate output may look a little stuttery, depending on how the source was filmed/created. Adding motion blur to each frame can help with this, smoothing the feel of the slower rate playback. This is done by setting ShutterBlur to 1,2 or 3, then specifying the shutter angle that you wish the output to simulate. However, as there may be some motion blur already in the source you also need to specify/estimate the shutter angle used in the source. Shutter angles range from 0 to 360, with 0 being perfectly sharp and 360 being fully blurred from one frame to next (artificial output shutter angles > 360 are supported to a very limited degree).

    Edit: A little late. This method is similar to pdr's option 1.
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  5. Member racer-x's Avatar
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    Dang.......3 posts within 3 seconds, that's got to be a record.
    The memories of a man in his old age, are the deeds of the man in his prime.......
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  6. Hehe, 3 minutes, I think.
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  7. Member
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    Wow - thanks for all the prompt replies!

    The reason I thought I'd shoot 50p is because in bright light it's not possible to maintain a slow enough shutter speed (1/50 sec) for 25p video on my RX100M2, as I can't attach a Neutral Density Filter. So I thought it would look a lot smoother using 50p, even if the shutter speed got very high.


    However, if half the frames are being discarded to convert back to 25p, I'm probably worse off than shooting 25p at 24 Mbps. 50p is 28 Mbps, so discarding half the frames would leave me with 25p at 14 Mbps - and to make matters worse the frame rate will still be too high so panning will look stuttery. Is my thinking correct here?


    Is another way to approach this to shoot 25p at 24 Mbps and add motion blur in post? If so, what's the best way to do this?


    Or is there no real solution other than to get a filter adapter for my RX100M2 (like the Magfilter) and use an ND8 filter when I'm in sunlight to keep to shutter speed down?


    Thanks for all the advice.
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  8. Member
    Join Date: Sep 2007
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    Originally Posted by Dave2ic View Post
    However, if half the frames are being discarded to convert back to 25p, I'm probably worse off than shooting 25p at 24 Mbps. 50p is 28 Mbps, so discarding half the frames would leave me with 25p at 14 Mbps - and to make matters worse the frame rate will still be too high so panning will look stuttery. Is my thinking correct here?
    In terms of bitrate - not exactly; because not all frames are allocated the same proportion of bitrate; and the GOP size is usually doubled for 50p shooting (resulting in better efficiency) - but the general idea is correct 25p @ 24Mbps would probably look better due to higher average bitrate per frame

    In terms of high framerates - If you pan from A to B over 10 seconds, it's the same amount of "stutter" or choppiness cadence wise (disregarding motion blur) whether or not you shoot native 25p vs 50p and take every 2nd frame

    Is another way to approach this to shoot 25p at 24 Mbps and add motion blur in post? If so, what's the best way to do this?

    Or is there no real solution other than to get a filter adapter for my RX100M2 (like the Magfilter) and use an ND8 filter when I'm in sunlight to keep to shutter speed down?
    Motion blur in post is always a gamble. Sometimes it works great, but some situations can be a nightmare. It's really content and situation specific. But if you can , real shutter blur is always better than synthetic

    Overall, for avisynth I would say most of the time QTGMC produces slightly better results than mflowblur. I would say 3rd party motion blur RE:Vision FX ReelSmart Motion Blur (for After Effects, but they might have versions for some NLE's) is slightly better
    Last edited by poisondeathray; 19th Jan 2014 at 15:21.
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  9. Member racer-x's Avatar
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    It really boils down to what your final format will be. If you will export to Blu-Ray, then 50p is supported at 1280x720 anyway. Personally I would shoot 50p as more options are available to you.

    Have you tried shooting in Aperture Priority and selecting a wide open aperture. This will require constant focus adjustments. Also you need to slow your pans (or eliminate them) and use a good tripod.
    The memories of a man in his old age, are the deeds of the man in his prime.......
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  10. Member racer-x's Avatar
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    .........Ooops just noticed this is a compact still camera (similar to my Sony HX9V) that also shoots video. Disregard my last post and maybe frame blur will be your best option.
    The memories of a man in his old age, are the deeds of the man in his prime.......
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  11. Member
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    Originally Posted by racer-x View Post
    It really boils down to what your final format will be. If you will export to Blu-Ray, then 50p is supported at 1280x720 anyway. Personally I would shoot 50p as more options are available to you.
    I don't really have any need for 50p, but I would like to ensure my 25p video doesn't get jerky by letting the shutter speed get too high in bright sunlight. I thought the additional frame data from using 50p would help with this if I convert back to 25p, but it seems this is not the case.
    If I want 25p I should shot 25p.


    Originally Posted by racer-x View Post
    Have you tried shooting in Aperture Priority and selecting a wide open aperture. This will require constant focus adjustments. Also you need to slow your pans (or eliminate them) and use a good tripod.
    But aperture wide open only increases shutter speed as it let's more light in. I need to stop down to decrease shutter speed, but even then I need another 2-3 stops to get as skew as 1/50 sec for 25p.


    So I don't think there's anything else I can do but to get myself a thread adapter with an ND4 or ND8 for my RX100M2.
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  12. post a small (moving) sample to give people something to try possible ideas.

    VHELP's - Sample Clips [last: 12.29.06],
    my YouTube videos
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  13. Member racer-x's Avatar
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    The idea of shooting with a wide open aperture implies getting a shallow DOF. Since this a compact digital camera, that throws that logic out the window, hence the reason I said to disregard that post.................

    I incorrectly assumed that this was a decent quality video camera................sorry my bad.
    The memories of a man in his old age, are the deeds of the man in his prime.......
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