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Sending DV to camcorder over firewire gives dropouts

AMD64 running FreeBSD 6.0 beta3.
Canon DV NTSC camcorder connected via firewire.

Playing a tape and recording it on the computer via

	fwcontrol -R filename.dv

appears to work fine.

Sending the video back to the camcorder via

	fwcontrol -S filename.dv

mostly works, but every 1.5-2 seconds or so I get a momentary
dropout of both video and audio.  I get the same dropouts
with a dv file created by "fwcontrol -R" and with dv files created
by ffmpeg.

This is with the camcorder in "VCR" mode, and stopped (not recording).
The computer is otherwise idle.

The dropouts are very regular and repeatable, so it probably isn't due to
an occasional transmission error, or the computer being busy for a moment.

Wild Guess Theory #1:

    fwcontrol -S reports:

	3948 frames, 131.50 secs, 30.02 frames/sec
	784 frames, 25.92 secs, 30.24 frames/sec
	3597 frames, 119.78 secs, 30.03 frames/sec

    Shouldn't this be 29.97 fps ?

Wild Guess Theory #2:

    Perhaps the flow-control / buffer-management isn't quite right,
    and the camcorder runs out of data?