Laurent,
I've notice that the buffer timestamps are obtained with
do_gettimeofday, this makes me a bit worried, if the system time
changes while streaming I believe this can cause a major error in the
time stamps, also on many systems gettimeofday uses the TSC, but on
some multicore systems the TSC on each core may be out of sync, in
which case the cpu you are running on may give a different
gettimeofday result than another cpu (this may explain the time drift
between consecutive frames in my quad processor)
You should use clock_gettime(CLOCK_MONOTONIC) instead of
gettimeofday() for interval timing, or just do like gspca and use
jiffies, this works very well since it's reference is boot time and
it's monotonic, it also seems more accurate than uvc, at least I don't
notice the same clock drift between consecutive clock frames.
The change for uvc should be easy enough:
--- uvc_queue.c 2009-11-27 00:26:13 +0000
+++ uvc_queue_patched.c 2009-11-27 10:06:47 +0000
@@ -20,6 +20,7 @@
#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <asm/atomic.h>
+#include <linux/jiffies.h>
#include "uvcvideo.h"
@@ -497,7 +498,8 @@
spin_unlock_irqrestore(&queue->irqlock, flags);
buf->buf.sequence = queue->sequence++;
- do_gettimeofday(&buf->buf.timestamp);
+ jiffies_to_timeval(get_jiffies_64(),
+ &buf->buf.timestamp);
wake_up(&buf->wait);
return nextbuf;
This change would be very much appreciated, since I'm struggling a bit
with matroska files in some video players (mplayer, vlc) they seem to
require perfectly synced timestamps, I guess they set the internal
clock to the given fps, gstreamer in the other hand works without
problems, it probably uses a higher and fixed resolution clock ( 1ms
??).
Video Captures from the few gspca cameras I've tested work without
major problems in any of these players.
AVI since it doesn't contain time stamps also works without issues.
Best regards,
Paulo
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