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AVCHD 1080p time lapse
  • You can shoot video in any mode and use software post-processing to apply any speed-up that you want. I shoot with a wide shutter angle and use frame blending to make the motion look smooth. This simulates severe undercranking with a 360-degree shutter.



    This particular example was shot on a hacked GH2 in AVCHD 1080p 24-fps mode with the shutter speed set to 1/2 s. That makes the recorded video have 13 frames for each picture taken, for an effective frame rate of 23.976/13, or about 1.84 fps. You can set the GOP length to 13 frames, which will give you one I-frame for each picture taken, and then use just the I-frames in decoding. That increases compression efficiency and gives you longer recording times. The shutter angle here is 332 degrees, or 92%, which isn't bad, but ideally you want to get closer to 360 degrees so that you don't have discontinuities in the motion trails. If I did this again, I would have shot 8-fps in 300% variable mode with a 1/8 s shutter speed. Using a lower frame rate of course means there is less video data that needs to be processed.

    Here's the video data flow:
    camera MTS -> Haali Media Splitter -> ffdshow tryouts decoder -> Avisynth -> makeAVIS -> Sony Vegas

    Here's my Avisynth script for doing 65x speed-up: 16.25x from undercranking and 4x from frame blending:
    DirectshowSource("input.MTS")
    SelectEvery(13)
    c1=selectevery(last, 4, 0)
    c2=selectevery(last, 4, 1)
    c3=selectevery(last, 4, 2)
    c4=selectevery(last, 4, 3)
    blend1 = Overlay(c1, c2, mode="blend", opacity=0.5)
    blend2 = overlay(c3, c4, mode="blend", opacity=0.5)
    Overlay(blend1, blend2, mode="blend", opacity=0.5)
    AssumeFPS("ntsc_video")


    Time lapse photography has practical applications. Say you are filming a car driving by at 10 miles per hour, but you want to make it look like it's going 60 miles per hour. If your target format is 24 fps with a 180-degree shutter, you can shoot 24-fps with a 1/25 s shutter, and then blend the first three frames of every six into one output frame. Or you can shoot 8-fps in 300% variable mode with a 1/8 s shutter, and drop every other frame. If the car is going straight down a road with no bumps or curves, the effect will be totally convincing. :)
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  • You can go even further, if you are willing to export to image sequences. :)

    One of my favorite approaches is to use averaging instead. There are tons of more complex programs for this purpose, but Photomatix Pro has a batch averaging mode that lets you combine anywhere from 2 to 12 exposures per frame (with the added benefit of noise reduction smoothing).

    The math is:
    # of exposures to average X 100% = playback rate as percentage

    So you can get 200% to 1200% playback rate easily that way.

    In my experience with both, the results are a lot more rewarding with averaging.
  • My approach uses averaging, and it lets you combine as many frames as you want.
  • Maybe I'm misreading your script: it looks like it's using blending, not averaging. I'll try it and then see if I misread it.
  • Simple blending *is* averaging.
  • Either my ability to test is compromised at this hour (which is entirely possible) or you're right (which is even more likely). :)

    There's a decent chance I got frame blending and field blending mixed up, in which case I apologize for the confusion. I'll check again when I'm a bit more alert.
  • my sample of 1/2 shutter video. Used After Effects and 'CC Force Motion blur' filter for frame blending
  • Looks great, shame this only works on the GH2 [on the GH1 1/2 second shutter can only be used in 720p 50/60fps mode]
  • On the GH1 you can still shoot 1080p AVCHD with a 1/30 s shutter and just use more frame blending to get whatever speedup you want.

    @Max, I really liked these time lapse videos of yours:

  • @balazer how long can you record if you would come to 2GB. Compared to the MJPEG (approx. 1 hour at 1080p, 2GB and 2ps) will you save lot more space on your card.
  • My GOP=13, S=0.5s 1080p AVCHD recordings were 40-60 minutes per 2 GB. But of course AVCHD doesn't stop recording at 2 GB like MJPEG does.
  • @balazer ....and it's real 1080p as it is assumed that MJPEG will extrapolate from 720p.

    Would it be too bad for the image to multiply GOP=13.
  • AVCHD 1080p is real 1080p. Lowering the shutter speed to 1/2 doesn't change that. Setting the GOP length to 13 yields the same video quality as GOP=1, since you get one I-frame per picture taken. Just make sure you use the I-frames in decoding. (my Avisynth script accomplishes that with the SelectEvery(13) expression)
  • @Max how exactly did you use the filter in AE?
  • @balazar Sorry if this is a newb question, but how exactly are you able to set a shutter speed of 1/2 second? With my camera, I'm unable to set anything slower than 1/25. Is there a hack option that I'm unaware of?

    Thanks!
  • @KeithLommel

    Manual focus allows for 1/2 second shutter. M mode too, I'm pretty sure.
  • @markmark1 in AE set video 'Stretch' to 2-5%. CC Force Motion blur with settings: Motion blur samples:8 (more - better but slower. depend on stretch value) Shutter angle - 180. Thats all
  • @Hallvalla Not sure by what logic manual focus is required to lower the shutter speed, but you're right. That did the trick. Thanks!
  • @balazer

    I am a nooby on timelapse. I really like your demo. May I ask some questions regarding the frame rate (fps) and shutter speed that you used.

    >This particular example was shot on a hacked GH2 in AVCHD 1080p 24-fps mode with the shutter speed set to 1/2 s. That makes the recorded video have 13 frames for each picture taken, for an effective frame rate of 23.976/13, or about 1.84 fps.

    I thought shutter speed had nothing to do with the fps. The shutter speed only had effect on exposure - darker or brighter. In another word, how long a frame is exposed. Is my understanding wrong? I could not understanding it from your statement I quoted above. If you shoot at 24-fps and shutter speed at 1/2s, would you not still end up with 24-fps with over exposed (possibly) frames? How would a 1/2s shutter speed give you "13 frames for each picture taken"? Would you mind explain this to me? I need to understand this.

    I am looking forward to your answer.

    Thanks.
  • @dusty42

    Let's pretend that we have nice even numbers with a 1/24th shutter speed for simplicity's sake.

    Think of it as film rolling through a camera. With the shutter opening and closing at different speeds but the rate the film goes through the camera remaining the same.

    24 frames per second. If the shutter speed was 1/24 you'd have a distinct frame for each 1/24 of a second- 24 different images.

    Anything below 1/24 would still have 24 frames but the individual frame images would be repeated. At 1/12 second shutter, you'd have 24 images but since the shutter was open for 1/12 second, there would be two repeated images for each time segment the shutter open and closed. 12 distinct images. Each repeated twice. Still 24 frames.

    Here with a 1/2 shutter, the shutter would open and close twice in a second. Therefore, since 24 frames still rolled through the camera during that second, there would only be two distinct images with each repeated for 12 frames.

    Any shutter time faster than 1/24 would of course still have 24 frames. Each frame would have a distinct image. But each frame would have been exposed for less time, resulting in a "darker" image.
  • @KeithLommel, long shutter exposurers require manual focus and manual exposure because automatic focus and automatic exposure rely on sampling the image at regular intervals. Technically I suppose you could have automatic focus and automatic exposure with long exposures/low effective frame rates, but they would be very sluggish.

    @chauncy, yes, but a shutter speed of 1/2 second results in one exposure for every 13/23.976 seconds, not for every 1/2 second.

  • @chauncy, thank you very much for your clear explanation. That made sense to me. However, balazer mentioned 13 frames for each picture taken at 1/2s shutter speed. That really confuses me. As you mentioned, for a 24fps mode at 1/2s, there would be 12 identical frames. How did balazer get "13 frames per picture taken" at 1/2s. Is this related to the fact that balazer has GOP 13?

    @balazer, would you mind explain it so I can understand?

    Thanks.
  • @balazer That makes perfect sense. Thanks for the educational and informative explanation!
  • Forget my previous explanation about why you get 13 identical frames when the shutter speed is 1/2 s. I was totally mixed up and had my math backwards.

    The bottom line is that when you set the GH2 to a shutter speed of 1/2 s, the camera produces 13 identical frames for each exposure, for an effective frame rate of 13/23.976 fps. I don't know why. Maybe the camera using an exposure time that is slightly longer than 1/2 s.

    Most of the shutter settings longer than 1/25 s exhibit the same kind of behavior in 24p mode, where you get one more frame than you'd expect for each exposure. I don't remember which ones.
  • @balazer thanks for your great explanations. Avisynth works really well, I let it work via virtualdub.

    Did somebody try to lower general bitrates and increase to multiple GOP13 (like GOP26, GOP39 etc.). Would that effect the image quality dramatically?
    That would be like going into the opposit direction of cbranding's 44M patch. Maybe you could end up with very long recording times even on small cards and almost no influence of image quality as one ends up with timelapse GOP2, GOP3 etc..

    Then it would be only a question of powering the GH2...