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Intraframe vs Interframe compression flame
  • This discussion was created from comments split from: Official GH2 "Stalin" hack development topic.
  • 32 Replies sorted by
  • @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.
  • If you guys are complaining about the 50/60p images looking too fluid...then..um...that's exactly what we want isn't it?
  • @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.
  • @bwhitz
    I am deeply sorry, but that you are telling about compression and B frames sounds like bullshit.
  • @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
  • @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
  • 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.
  • @bwhitz
    This is why I asked you to read books.
    Just try to use MJPEG keeping the same bitrate and then compare it with "so bad" large GOP AVCHD :-)
  • @bwhits What you are seeing ("sliding") has nothing to do with the b-frames, it has to do with low bitrate. You know, if it was true what you said, you would see the same issues with the Blu-ray disk movie releases.
  • @dkitsov "You know, if it was true what you said, you would see the same issues with the Blu-ray disk movie releases. "
    Good point, I certainly don't see an issue there.

    @bwhitz "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. "

    I see nothing that makes the Canon more filmic, especially claiming its due to higher compression. LOL! It's just the opposite.

    I'm certainly not interested in hearing about Canon 7D in this topic.
  • Very interested in what you mean though, proaudio4, could you maybe share an example where it's very visible (maybe in new topic)?
  • @edun
    You're mixing me up with who I'm quoting. I agree with you. LOL!

  • Here is my example of intraframe gh13 video with gop set to 1 (last message). May be it will be useful for your discussion.
    http://personal-view.com/talks/discussion/166/is-a-pseudo-i-frame-codec-possible-with-gop1#Item_27
  • @edun It's not visible in the sense that macro-blocking is... it's more like parts of the image aren't changing from frame to frame. For example, if there are building's in the background of some shots, it looks like they stay still and just "shift" around from frame to frame instead of refreshing as a new image... or like parts of the image are getting "cut-out" and repositioned. In cinematography terms, it's almost like part of the image is shot at the traditional 1/50 shutter, while the rest is a lower shutter speed, like 1/30.

    @telkitachki The motion of your GOP1 looks nice! More like real digital cinema motion, than an inter-frame stream. Hoping to do this with the GH2! I'll play around with this once I get Windows (or figure out Winebottler) on my Mac...

    At, VK's request I'll start a new thread... I don't want to de-rail this one anymore.
  • Here you are. Feel free to flame about this.
  • Here we call it the Soap Opera effect.

    On a 120 Hz TV with the motion interpolation turned on, this means that 4 out of every 5 frames displayed on the TV were artificially filled in by the video processor, not native to the source. That creates the "soap opera effect" -- making something originally shot on a 35/70mm film camera look like it was created on a cheap camcorder. It might smooth out the panning shots, but it also washes out a lot of the fine detail and completely changes the look and feel of a movie.

    The perspective that most professional reviewers come from is that theatrical presentation is the reference standard. And that's also the reference that movie directors and cinematographers come from as well. Everything in the production and post production chain is optimized around what the movie looks like in the theater. And in most cases, that holds true for the home video versions as well.
  • @Bueller
    That are you talking is not related to compression, but rather frame interpolation.
    It is completely different thing.
  • I think it's all a matter of personal preference. There's no way I'll accept an argument from anyone about GOP length on the GH13 or GH2. Shorter AVCHD GOPs look much more filmic to ME when shooting moving images, period. I've shot with all GOP lengths and 3 for the GH13 and now the GH2 is what I prefer. It's entirely subjective though. When I show GH1/2 tests to my younger friends they don't feel that way, so no right or wrong here. It's an image quality vs. perceived temporal quality debate. I totally get that shorter GOP in a given data rate means less image quality. My hope is that when Vitaliy's new patch allows us to double the average 24p bit rate, my current 3 GOP setting will hold up. The temporal feel of the action is more important to me than image quality but I totally get most folks may feel the opposite. I've been working on feature films for 30 years so I have a built-in, old school bias that may be totally inappropriate in today's digital world. What's nice about the Gh1/2 is that it allows us to shoot any kind of look we want in extremely high quality - temporal or visual.
  • @kae

    I'm totally with you. I also prefer higher temporal quality and motion, to overall data-rate. AVCHD-inter looks to me almost like the mentioned "Soap Opera Effect" with 120hz TV's... although not nearly as bad. Did you post your GOP 3 settings anywhere for the GH2? I'd love to try them out and shoot some comparisons maybe...
  • @telkitachki Your video looks really nice!
  • @telkitachki's video is exactly the look I am talking about. Incredibly filmic in a temporal way to my eye. I wasn't able to play back GOP 1 footage I shot with the GH2 in cam or computer or I would shoot that way all the time. Lowest GOP I could go to was taking Kris C's 70mbit settings found here: http://www.personal-view.com/talks/discussion/50/official-gh2-stalin-hack-development-topic/p12, changing everything he had at 70000000 and making it 50000000. Then changing the 108024p GOP setting to 3. As I stated earlier, going lower than that wasn't playable on computer or cam. 3 was lowest I could go. Next playable GOP setting was 6, but I like 3 better - temporally, at least.
  • Yes VK you are right, I was just purely illustrating for others the visual effect that the original poster was referring to.
  • Hi Friends,

    I don't think there is any reason to flame or be upset about this. I am interested in the implementation of GOP1 because Telkitachki's GOP1 videos look very nice, and I think the hardware in the GH2 might be capable of a sustained 40-50mb all iframe recording... What does everyone else think?

    Here is the Wiki on AVC-intra:
    http://en.wikipedia.org/wiki/AVC-Intra
  • @bannedindv

    Yea, I don't know why people started saying we were flaming... we just started talking about b-frames and how some of us don't like the motion they can create. I did say "death to b-frames!" but that was pretty much just a joke/sarcasm.

    But yea, all I-frame ecoding would be amazing! ...even if the bit-rate is lower than with the inter-frames.

    BTW, kae has mentioned that GOP 1 setting doesn't work... but multiples of three seem to. Has anyone tried a value of GOP 0? Maybe? I would try it myself, but WineBottler is not working. It's missing all the Winetricks. I guess it's a bug in snowleapord. I'll just have to run a copy of windows with bootcamp I guess.
  • bwhitz said: "B-frames basically just save the changes in motion from the previous frame, the rest of the frame just kind of slides around. "

    The sliding effect you're referring to does occur in videos that are excessively compressed and starved of bitrate. When restricted to extremely low bitrates, an AVCHD encoder will resort to its most efficient compression techniques. An encoded B-frame may contain virtually exact copies of areas found in nearby frames, with slight shifts in position to track object movements.

    With adequate bitrate, however, an AVCHD encoder will use motion vectors from nearby frames only as an initial approximation of areas in the B-frame it is encoding. It will use additional techniques to refine B-frame image details to match the image quality of an I-frame. When necessary, the encoder can use the same intra-frame compression on selected B-frame macroblocks that it uses to encode I-frames. At high-quality bitrates, B-frames are visually indistinguishable from I-frames.