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From: Alastair M. <am...@pe...> - 2001-11-16 19:04:45
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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 |