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    Originally posted by Barry_Green View Post
    Totally disagree. Of course a P-frame can be much higher quality than the I-frame.
    Usually not higher quality that the I-frame it's using as reference, unless you have a very low I:P ratio. You said earlier the P-frame directly following the "mushy" I-frame improves on it. This usually isn't the case.


    The P-frame is not targeted to match the I-frame, it's targeted to match the raw uncompressed
    frame that's fed to the coder.
    But you're looking at the GH1 encode, not the uncompressed frame fed to the encoder. You're examining and decoding the GH1 stream, not the preceding generation of video; so the P-frame is matched to the I-frame. Farther on in the GOP, each P-frame is matched to the preceding P-frame if reference frames=1 . The 1st P-frame is matched to the I-frame. In the streams I have seen , this firmware uses 1 reference frame. This means that P-frame can only use that IDR-frame or preceding P-frame as reference. (It cannot use 2 P-frames away for example).

    A P-frame looks at the changes between the previous frame, and the target frame. If the target frame is incredibly complex, and the previous frame is mushy, the P-frame will use its bandwidth to encode the changes between the mushy frame and the detailed reference frame.
    Yes, this is true, you need more bandwidth to code the residual. (i.e need more bitrate for P-frames if there is higher scene complexity). It's a balancing act, between I:P and P:B ratios (P:B doesn't apply here). If you take too
    much away from the I-frame, the keyframe looks poor, but the following frames in the GOP will also look poor if they do not have enough bitrate. If you use too much for the I-frame , the video deteriorate as you proceed in the GOP, as the P-frames do not have enough bitrate

    Each frame in the GoP does not care what the prior frame looks like, it instead cares what the
    target frame (the uncompressed image) looks like, and makes its best effort to look like that target
    frame. So yes, cyclic codec pulsing is very possible if the I-frame does a poor job on the first frame
    in the GoP.
    But it does care what the prior frame looks like. It uses the prior frame as a reference, and it codes the residual between that reference and what is predicted; otherwise every frame would be called an I-frame and not a P-frame If you had higher # of reference frames, it could use P-frames as reference farther away and coding would be more efficient. If you had B-frames, you could use them in both directions and this would be even more efficient in theory.

    In the clip I will post, you can watch it happen. The keyframe (I-frame) looks horrible because it's
    got nowhere near enough bandwidth to represent the image properly. Then the P-frames bring it
    successively up to snuff, adding more and more detail, until - smack, 15 frames later, the cycle
    starts all over again with a lousy I-frame.
    Whereas if the I-frame was a good-quality image in the first place, then the P-frames would have
    very little work to do to maintain that quality image throughout the GoP.
    I see what you're saying. The "textbook" case of keyframe pulsing is high I-frame allocation, and low P-frame allocation. The quality slowly deteriorates proceeding along the gop until the next high quality I-frame and it "pops" into focus and high quality. This is the far more common scenario, you even see it in retail blu-ray , online on vimeo, youtube etc... I apologize for the mixup, I should have read your description more clearly
    Last edited by PDR; 06-14-2010, 11:17 AM.

    Comment


      Originally posted by PDR View Post
      I see what you're saying. The "textbook" case of keyframe pulsing is high I-frame allocation, and low P-frame allocation. The quality slowly deteriorates proceeding along the gop until the next high quality I-frame and it "pops" into focus and high quality. This is the far more common scenario, you even see it in retail blu-ray , online on vimeo, youtube etc... I apologize for the mixup, I should have read your description more clearly
      Yeah, that's the exact opposite of what we're encountering. Quality is awful for a frame and then slowly improves, until it "pops" back mushy on the next I-frame.

      That's why I say that for this case, what we really need is more bandwidth allocated to the I-frame. This may not be relevant to long-GoP in general, but in the specific case of the GH1 it seems to be exactly the medicine for the problem at hand.
      ..
      The AU-EVA1 Book - The DVX200 Book - The UX180 & UX90 Book - Lighting For Film & TV - Sound For Film & TV

      Comment


        Can you please still upload the clip Barry? I'd still be interested in seeing it

        I know the initial few seconds can be problematic as you start recording, but does this occur as bad throughout even 5-10 seconds later?

        I sold my GH1 a while back , but these recent developments have seriously piqued my interest!

        Comment


          Codec "pulsing" file uploaded
          http://www.mediafire.com/download.php?n21jdyznv2w
          ..
          The AU-EVA1 Book - The DVX200 Book - The UX180 & UX90 Book - Lighting For Film & TV - Sound For Film & TV

          Comment


            I can't seem to find anything/anyone that speaks about the Lumix's HDMI out while recording. What's it doing? Full-res? Any menu-stuff on-screen?
            Thanks.

            Comment


              There is no hdmi while recording

              Thats what Tester13 is looking into

              Comment


                Originally posted by LeavingTheCandy View Post
                I can't seem to find anything/anyone that speaks about the Lumix's HDMI out while recording. What's it doing? Full-res? Any menu-stuff on-screen?
                Thanks.
                http://www.dvxuser.com/V6/showthread.php?t=212263

                Comment


                  Originally posted by Barry_Green View Post

                  Thanks for uploading that.

                  This stream has errors. There are frame repeats before the "truncated" I-frames in the previous GOP. Not all I-frames are low quality, there are "normal" looking GOP sequences, which do not have frame repeats.

                  In this example frame 11+12 are frame repeats (as are all the others before the "truncated" I-frames , 23+24, 35+36, etc...)



                  What settings did you use for this clip?

                  Do you have a longer example? I alluded to bad frames at the beginning of recordings - this is common and can occur even in other camcorders, and the unpatched GH1 - but not to this extent. It's not limited to the beginning or "warm up" period either - There is a bad I-frame even in the middle of the clip surrounded by "normal" I frames. (you can see it "shortened", in this graphical representation the height corresponds to the coded frame size, red frames are I-frames, blue are P-frames)

                  This stream also has buffer underrun errors. Normally this isn't a problem for PC, but some devices and hardware decoders may have issues decoding it.

                  This stream also has incorrect FPS at the bitstream level, may cause sync issues on longer compositions and in some NLE's

                  Also, it uses 22 slices/frame => can cause problems with some decoders which usually max out at 16
                  Last edited by PDR; 06-14-2010, 01:40 PM.

                  Comment


                    That's the only clip I have that has the pulsing in it. I don't remember the exact settings, but they were the "D" settings when those were first announced.
                    ..
                    The AU-EVA1 Book - The DVX200 Book - The UX180 & UX90 Book - Lighting For Film & TV - Sound For Film & TV

                    Comment


                      I had similar pulsing and macroblocking on the "D" settings as well.

                      Comment


                        i experienced the pulsing when shooting 720p50 at frist 2-3 second which skip one of two frames. so i recall my setting and remember the shutter speed below 1/50. my cam is patched to "D" setting. then examed the pervious footages at both 1080p25 and 720p50 and found normal.

                        i am trying to duplicate the pulsing situation, any idea of it?

                        Comment


                          i've had this pulse since i first got my GH1 also with the GH13 always noticeble in 720 60p (high detail scenes ) all the way through clips. to be honest i haven't noticed it in FHD.
                          can it be fixed?

                          Comment


                            PTool 3.36 Updated without version change.

                            Changed status of Version Compare patch. It is advisable to use it instead of increments for GH1.
                            MJPEG Encoder patch removed from list, will be applied automatically upon MJPEG width and heigh change.
                            Video Buffer patch removed.

                            Comment


                              Great Tool adjustments. About to check MJPEG tomorrow.

                              Tester: so Video Buffer was doing nothing at all? When I tested, and reported back, anything over 40 would give my camera errors, but people are using 84 and having no issue.

                              Nice Avatar. Haha.
                              Comet Color Page
                              Allow me: fanboy of great images.

                              Comment


                                Originally posted by Kholi View Post
                                Nice Avatar. Haha.
                                Yeah, with some meaning in it.

                                http://www.youtube.com/watch?v=fgX-7ebLOdw

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