Capture DV stream to disk (unprocessed)


    May 29 2006 | 10:36 pm
    Hi, we are working on a project where we capture live video from a DV camcorder to a buffer. From this buffer we play back the frames with some not-too- complicated proccesing. We intend to go from DV to 720p or 1080p, budget permitting. Playback starts before capturing has ended. So it is read-while-write.
    The delay between capture and playback is 4 to 10 minutes. So the buffer has to be disk based, not RAM based. We chop the footage up into one minute segments, to deal with simultaneous reading and writing, and to deal with variable delay times. No problem here.
    We want to store the frames on disk in compressed form, to reduce disk I/O. Ideally we capture a DV compressed frame from FireWire and store it as-is on disk. This we managed to do with WinDV. http://windv.mourek.cz/ In fact this is what most capture apps do, like the one you have in iMovie or FCP. The special thing about WinDV is that it does the chopping for us, every N frames.
    We did not manage to do this with [jit.dx.grab]. It is possible to capture frames to disk without decompressing and recompressing this way, but it is not possible to chop up the incoming stream. if we try to change the file captured to, by first closing the current file, and opening a new file, all within one frame as not to drop any, we get "jit.qt.grab error -9402 setting bottlenecks"
    The problem with the WinDV solution is that it is not possible to encapsulate it into one idiot-proof max standalone. Right now we have a very arcane solution to control WinDV from max, which is easily broken.
    Does anyone here have a solution to capture and chop a DV stream to disk under max control? aTdHvAaNnKcSe -jennek

    • May 30 2006 | 3:41 pm
      Hi,
      Have you considered appending every newly grabbed movie to your currently playing movie with [jit.qt.movie]'s insert command? This way you construct your currently playing movie with a series of quicktime references, saving disk space.
      For the frame dropping i'd say route your [jit.qt.grab] through a gate to two alternating [jit.qt.record]s.
      Cheers, Mattijs
    • May 30 2006 | 6:57 pm
      > On 30 May 2006, at 17:41, Mattijs Kneppers wrote:
      > Have you considered appending every newly grabbed movie to your > currently playing movie with [jit.qt.movie]'s insert command? This > way you construct your currently playing movie with a series of > quicktime references, saving disk space.
      no we have not considered it. While I understand what reference movies are, I fail to see what benefit it would bring in this situation
      > For the frame dropping i'd say route your [jit.qt.grab] through a > gate to two alternating [jit.qt.record]s. this will work for the file splitting, but it wil decompress and recompress every frame, which is a waste of CPU that we cannot afford.
      Thanks for your reaction -jennek
    • May 31 2006 | 12:23 pm
      > no we have not considered it. > While I understand what reference movies are, I fail to see what > benefit it would bring > in this situation
      I was wondering how you would bring the chopped captures back into the patch. Appearantly you have already found another nice solution for that.
      > this will work for the file splitting, but it wil decompress and > recompress every frame, which is a waste of CPU > that we cannot afford.
      I can imagine. I can not think of another solution though. I tried two alternating jit.qt.grabs in the patch below. It works, there are no (troublesome) errors but it misses frames.
    • Jul 12 2006 | 2:12 pm
      HI,
      I have a similar problem. The difference is I am using a webcam to get stream video. I tried mattijs's patch and I got an error with Jit.qt.grab: no grabber component is currently open.
      The whole patch looked like working well. the two toggles on the left of two jit.qt.grab objects were turning on/off alternatively. But there's no record in the directed folder.
      Could you explain it for me? I'm an anxious student and Max beginner. Looking forward to your response! Thanks!
      amy
    • Jul 12 2006 | 5:43 pm
      On Jul 12, 2006, at 9:13 AM, Xinmei wrote:
      > > HI, > > I have a similar problem. The difference is I am using a webcam to > get stream video. I tried mattijs's patch and I got an error with > Jit.qt.grab: no grabber component is currently open. > > The whole patch looked like working well. the two toggles on the > left of two jit.qt.grab objects were turning on/off alternatively. > But there's no record in the directed folder. > > Could you explain it for me? I'm an anxious student and Max > beginner. Looking forward to your response! Thanks!
      Jitter Tutorial 21 should answer all your questions - even the ones you haven't thought of asking yet.