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#17 Recording DV can be garbled if ...

Jeff Jackowski

Recording DV can be garbled if the recording starts
while the device is playing a blank spot on a DV tape.
The garbling affects the entire recording, not just the
begining. The audio and video are out of sync and jump
back and forth in time. I have a sample and can make
more because the bug is consistant. I am wiling to send
a sample. I have a fast connection to help with that.

The reason I was even trying to record during the blank
spot was to try to get the time codes on Broadcast 2000
to match the time codes recorded on my mini DV tape, or
at get consistant time codes from recording the same
taped segment. The result would be that I could edit
something, render it, delete the DV file from disk, and
keep the master on tape for later. The cut up HTAL file
could be used again if the master is rerecorded because
it would still define the same parts to cut.

I know this may actually be a bug in some DV library,
but since I don't program with them, I don't know. I
figured this would be a good place to start.


  • Logged In: YES

    The DV recording in Broadcast 2000 is done with DVGrab, the
    official DV recording utility
    for Linux so debugging the software may not solve the
    garbling. There
    is a way around the problem though. What you really need is an
    arbitrary point in the movie at which two media files need
    to show the
    same frame.

    That arbitrary middle point can be where the time code says
    the blank part, or it can be in the middle of your footage.
    Once you
    match this point then you know every point from the start of
    the file
    to the end of the file is synchronized.

    Try recording the DV footage in a non-blank spot, play the
    until you reach some important frame, possibly the beginning
    of a
    scene. Delete all the footage before that frame so your
    movie begins
    with the key frame. Now save this truncated movie as an
    htal file.

    Delete the media file from disk and recapture it starting from a
    non-blank spot, somewhere around the spot you started your last
    capture, so you'll get almost the same footage timeshifted.

    Now bring the latest file into the editor, find the
    important frame you
    found last time, cut all the media up to this frame, and
    save it as
    another htal file.

    Load the two htal files in text editors so you can see the


    for the Video 1 track in each file. The STARTSOURCE will be
    in each file even though they both show the same frame.

    If you subtract both STARTSOURCES you'll get a number of
    frames to add
    or subtract from the latest media file to make it conform to
    the same
    region of tape as the first file. If STARTSOURCE for the
    new file is
    9001 and STARTSOURCE for the old file is 3085 you need to
    subtract 5916
    frames from the start of the new file to reproduce the old file.

    Remember to subtract frames you cut and to add frames you paste
    silence. Once the start of the new file is adjusted on the
    timeline, render it as a
    "Direct copy DV" with 16 bit audio. The file you render
    will have the
    same time offset as the media file you deleted.

    • status: open --> closed-out-of-date