Hello Justin,
Thursday, June 07, 2001, 12:12:04 AM, you wrote:
JS> Eugene Kuznetsov wrote:
>>
>> Hello Justin,
>>
>> Wednesday, June 06, 2001, 7:12:18 AM, you wrote:
>>
>> JS> CSYNCing frames as soon as possible, and timestamping them,
>> JS> then copying them into a userspace buffer - which is a hideous waste of
>> JS> processing power.
>>
>> According to my measurements, 3-5% of CPU with Celeron 700, 640x480,
>> 16-bit, 25 fps. I wouldn't call it _hideous_...
JS> That is quite significant when you realise that the entire QTrec
JS> (without buffer copying) would only use around 35% - 40% CPU time.
For somebody who's aiming at maximum possible resolution/framerate CPU
time will be close to 100%.
>> JS> Yes, but this won't cope with transient latencies. If the capture
>> JS> thread doesn't get run for a couple of hundred milliseconds, you can
>> JS> develop quite a skew in the timestamp
>>
>> You can detect a hole in timestamps and copy the same frame several
>> times to compensate it.
JS> Yes, this is done, but the problem is that when the CSYNC thread catches
JS> up, it will timestamp the backlogged frames with nearly identical
JS> times. This is possible to fix, but it would require a lot of rules to
JS> try to gues the right timestamp. I will say it again - this should be
JS> done by the kernel driver - that is the only place the true timestamp is
JS> known.
Then don't do this in CSYNC thread. What's wrong with the following:
1) CSYNC thread ensures that all frames come in the correct order (
with increasing timestamps ),
2) when main thread sees that timestamp of next frame minus timestamp
of last encoded frame is >2./framerate, it writes as many null frames
as necessary to get back in sync.
BTW I will try v4l-enabled version ASAP..
--
Best regards,
Eugene
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