[libdv-dev] FYI: DV files and Dazzle Hollywood wierdness

[Alastair M. <am...@pe...>]

Hi,

  To save anyone who might be doing something similar the week of
hair pulling and head banging that it took me to figure it out,
I thought I'd mentioned the wierd problem I found with some DV files.

  First some background:  I have an app that, in part, creates a
videotape assembled from a selection of video clips stored in raw
DV format, using "dvconnect -s" to send them via 1394 to a Dazzle
Hollywood DV bridge that converts it to composite video and audio
for input to a (computer controlled) VHS recorder.

  Throughout development and testing, this process worked fine.
Install it at the customer site, load up the latest video clip
data, and we started getting dropouts as the DV bridge lost synch.
(An annoying quirk of the Dazzle box is that it takes about 5 seconds
to start sending video out after the start of a good DV data stream,
I set the system up to send 10 seconds of black first to get
around that.)

   After eliminating likely causes (eg data underruns because of
the disk not keeping up, etc -- tweaked with hdparm) we were still
getting the problem.   

   Finally (after much hair pulling, gnashing of teeth, etc, etc)
I determined that the *last frame* of each clip was bogus: all the
AAUX, Audio, etc flags were set to zero -- which caused the firmware
in the Dazzle box to hiccup and drop the output for a few seconds.

   I wrote a quick'n'dirty script to eliminate the last frame of
each file (just calculating the size and using "head") and after that
everything worked fine.

   Now, I wish I could tell you *why* the DV files had that funky
zeroed last frame.   The digitizing was done by a third party 
video shop in Hollywood, I just received a hard-drive with the
(approx 30 GB) of video clips on it.   If it's any clue, the drive
was in NTFS format so whatever they did the conversion on was
Windows-based.  (BTW, the video was originally shot/edited in NTSC
but converted to PAL since that's what the customer needed.)

   Just thought you might like to know.   I wish the Dazzle Hollywood
*didn't* discard the first few seconds of video after a change in
the format of the datastream, but that's something I can live with
(and aside from that, it's a very nice box for the price -- and about
the only one in its price range that supports both NTSC and PAL).

 Cheers,
   -- Alastair