On Monday 09 May 2005 22:55, Chris Kennedy wrote:
> This seems to depend upon something, I think it's whether or not the
> computer is very active with the CPU doing other things. I have seen it
> really good during a playback and really horrible with the same exact
> playback. It was just a cat /dev/video0 > /dev/video16 process when pretty
> good, but when running Myth (which really wouldn't have anything to do with
> Myth directly, just the CPU usage, from the vbi work queue), it was pretty
> bad at CC output. So really good compared to before, still some problems
> and probably missing buffers Hans has seen.
Check the timing in vbi_work_handler, which is the task that sets the CC regs.
If it jitters a lot, then it may be related to workload. BTW, what linux
version are you using, 2.4 or 2.6? I think that VBI passthrough support is
very hard (if not impossible) to get to work on 2.4 due to the lack of work
queues. I'd certainly put 2.4 support on the bottom of the to do list.
Another possible cause of timing problems (needs testing to verify!) is that
the passthrough hanling should be triggered by the VSYNC interrupt instead of
by the RE_INSERT (i.e. the reinsert just stores the data, but the VSYNC
starts the workqueue). I do not know how well the reinsert is sync with the
VSYNC. Remember that CC handling is very sensitive to timing. I think
outputting some timestamps from both VSYNC and the vbi_work_handler might
give you a good idea what the timing behavior is.
Two other questions:
1) is the NTSC widescreen signal (in the XDS data) passed on correctly?
2) how is the CC synchronisation on the TV? I do encode a PTS value into the
mpeg stream but I noticed that it has no relation to the PTS values in the
video/audio parts of the MPEG stream :-(
I'm glad your looking at this. It always bugged me that I could never finish
CC support even though I'll never use it :-)
Hans
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