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  1. Member
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    Stockhom, Sweden
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    All consumer video cameras (HD/HDMI) that I have come across (in PAL-land) can record in "50i", that is 25 interlaced frames/second.
    My own hands-on experience tells me that when the cameras are configured in that way, the live video on the HDMI port will also be 50i.

    However, I have recently had reports that some recent models (e.g. Canon Legria) will output 50p on the HDMI live output regardless of the recording being 50i.

    This whole interlace thing is of course an historic artifact, but for my specific application it is really a useful feature.
    (If I capture 50i and de-interlace it, I can achieve 20 ms timing resolution (50 fields/second) with half the data bandwith of 50p which gives 50 frames/second)

    Anyone with insights on this?

    /JS
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  2. Bandwidth is the entire reason interlaced video exists. But once you start talking compressed video the bandwidth differential is much reduced, maybe even eliminated. Interlaced encoding is less efficient than progressive encoding. And at 50 fps progressive you can get away with less bitrate per frame to get the same visual quality vs. 25 fps.
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  3. Member
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    Originally Posted by jagabo View Post
    Bandwidth is the entire reason interlaced video exists. But once you start talking compressed video the bandwidth differential is much reduced, maybe even eliminated. Interlaced encoding is less efficient than progressive encoding. And at 50 fps progressive you can get away with less bitrate per frame to get the same visual quality vs. 25 fps.
    Well, I am not talking about compressed video, since the HDMI live output is uncompressed.
    There is some chroma sub-sampling , but that is all.
    So, at 50p and 1920*1080 you are asking a PC to transfer a lot of data when capturing...

    /JS
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  4. Originally Posted by jmstack View Post
    at 50p and 1920*1080 you are asking a PC to transfer a lot of data when capturing...
    If that's your issue then you have no choice.

    Originally Posted by jmstack View Post
    There is some chroma sub-sampling , but that is all.
    And then you have all the problems and artifacts inherent in deinterlacing later.

    Originally Posted by jmstack View Post
    Well, I am not talking about compressed video, since the HDMI live output is uncompressed.
    Even if you capture uncompressed, you are likely going to compress the video eventually. If you use interlaced YV12 chroma subsampling (pretty much all distributions formats are YV12) you'll have spacial distortions as scan lines that are not next to each other are treated as if they are in interlaced YV12 encoding.
    Last edited by jagabo; 9th Nov 2017 at 10:04.
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  5. Member ChapmanDolly's Avatar
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    My Canon Legria G40 outputs both interlaced or progressive to HDMI depending on which is selected. All my video is done at 1080 50p 35Mbps and my PC has no problem running this. The big difference is that the internal video recorded on the SD cards is at 8 bit 4.2.0., whereas the HDMI output is 10 bit 4.2.2 which is great for recording high quality onto an external recorder in Prores or DNxHD.
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