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  1. Here are the file sizes I am getting when encoding an interlaced video at two different frame rates:

    1080i 59.94 534,142 KB

    1080i 29.97 478,373 KB

    Shouldn't the 29.97 file be smaller than the 59.94 file by a factor of 2, more like 267 KB?

    Ideally interlaced video would refresh even-numbered lines every 1/60 second and odd-numbered lines every 1/60 second. This is called the field rate, thus the complete frame is updated every 1/30 second, the frame rate, at least that's the way it worked in analog. Is digital/ffmpeg any different?

    ffmpeg code:

    Code:
    ffmpeg -y -i input.mp4  -crf 17  -c:v libx264  -pix_fmt yuv420p  -s 1920x1080  -r 59.94  -flags +ilme+ildct  -vf  unsharp=luma_msize_x=7:luma_msize_y=7:luma_amount=0.25,eq=brightness=-0.03:gamma=1.15,lutyuv=y='clip(val*1.06,0,236)'  -c:a ac3  clipped.mp4
    Code:
    ffmpeg -y -i input.mp4  -crf 17  -c:v libx264  -pix_fmt yuv420p  -s 1920x1080  -r 29.97  -flags +ilme+ildct  -vf  unsharp=luma_msize_x=7:luma_msize_y=7:luma_amount=0.25,eq=brightness=-0.03:gamma=1.15,lutyuv=y='clip(val*1.06,0,236)'  -c:a ac3  clipped.mp4
    Interlace was a trick they developed away back in the 1940's to increase vertical resolution without increasing bandwidth (in the U.S. they were restricted to a 6 MHz TV channel.
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  2. x264 is frame rate aware. It uses higher quantizers for higher frame rates. And in the real world, there's no such thing as 59.94i -- it's just the new name for 29.97i.
    Last edited by jagabo; 14th Jun 2018 at 22:14.
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  3. Here is a more complete set of file sizes:

    1080i 59.94 534,142
    1080i 29.97 478,373
    1080p 59.94 523,538
    1080p 29.97 523,611

    there's no such thing as 59.94i -- it's just the new name for 29.97i.
    So I should get the same number for both, right? I'm getting:

    1080i 59.94 534,142 KB
    1080i 29.97 478,373 KB
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  4. Oops, I made a mistake in my previous post. I started to say x264 uses lower quality per frame for higher frame rates but then decided to talk about quantizers instead of quality. But I forgot to change "lower" to "higher" (I'll fix the original post) . x264 uses higher quantizers for higher frame rates. So each frame is lower quality. The idea being you are less likely to see defects when they are displayed for a shorter period of time.

    Every camera etc. that claims to shoot 60i really shoots 30 interlaced frames per second. Once one company started calling that 60i all the others had to follow -- or lose sales to clueless consumers. Obviously, one can make a 60i video. Or any other frame rate, interlaced or progressive. So I don't know what you really have.

    Generally, interlaced frames don't compress as well as progressive frames (at the same frame rate). The "half bandwidth" deal is only valid with analog video. Once you start using compression the story isn't quite as clear cut.
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  5. Here is what I get with libx265:

    CRF 9
    h.265
    1080p 59.94 1,231,820 KB
    Last edited by chris319; 15th Jun 2018 at 04:56.
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