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Intraframe vs Interframe compression flame
  • 32 Replies sorted by
  • bwhitzbwhitz
    Sorry if I'm de-railing the thread, but all the books in the world wont change what I'm seeing. I'm not engineer, I'm a visual dp/director guy... I'm just trying to explain what I'm seeing with inter-frame vs intra-frame compression. I understand them from a technical perspective, but from an artists eye, they don't look right.
  • Vitaliy_KiselevVitaliy_Kiselev
    @bwhitz
    Please make some topic in Offtopic category if you want to discuss how bad are B frames.
    But try read any book about video compression first, ok? Otherwise it looks stupid.
    You can find some references in http://www.personal-view.com/talks/discussion/366/avchd-quantization-process
  • bwhitzbwhitz
    @Vitaliy How? Motion compensation/vectors have a distinct look to them. Ian_T and I both have noticed it. I may have explained it wrong, because I'm not a technical expert, but the GOP length does effect the overall look of the motion. You can see it clearly with the AF-100... the internal AVCHD, has a very video-like motion to it, but with an external recorder, and intra-frame recording, the motion is much more film-like and pleasing.

    Also, you can see this effect with the GH2... use the burst mode to capture a 40fps sequence, then assemble it as a video and compare it to the AVCHD motion. It's very different, because there's no motion vectoring going on.

    http://en.wikipedia.org/wiki/Inter_frame
  • Vitaliy_KiselevVitaliy_Kiselev
    @bwhitz
    I am deeply sorry, but that you are telling about compression and B frames sounds like bullshit.
  • bwhitzbwhitz
    @Ian_T No, we're talking about ways to improve upon the 24p mode to make it look more filmic. Film motion is more like the rapid succession of still frames. b-frame's and longer GOP's create a fluid interpolation or blending effect that causes the motion to look more "video-y". B-frames basically just save the changes in motion from the previous frame, the rest of the frame just kind of slides around. It's a great idea and helps to cut down on the size of the video, but it's not the most desirable looking motion for narrative work.

    Here's a better explanation... look at the "illustrated example". This is what we're trying to avoid.

    http://en.wikipedia.org/wiki/Motion_compensation

    Complete intra-frame compression (or as close as possible) is the best for acquisition.
  • Ian_TIan_T
    If you guys are complaining about the 50/60p images looking too fluid...then..um...that's exactly what we want isn't it?
  • bwhitzbwhitz
    @kae Thank you for bringing this up! Everyone seems to talk about how much more "efficient" b-frames are, but they completely destroy the film look! I hate them! It makes the video look as if it's sliding around instead of a sequence of independent images... I would much rather have a lower bit-rate if the GOP can be eliminated for good. Is that even possible though? Or is the GH2's AVCHD encoder hard-coded to always write GOP's? At least removing the stupid B-frames would be nice... efficiency isn't everything. Death to B-frames!

    I'd love to help out with the testing, but I cannot find anything like Streamparser for OSX... I'll probably just have to get windows on one of my drive partitions or something.

    Also, is it possible to run Canon 7D/5D footage through streamparser? I have a feeling that the "inadequate" codec everyone complains about in the Canon DSLRs is exactly the reason they look so filmic. I'm guessing the GOP is very low, around a 3-4, and b-frames are probably absent.
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