[gstreamer-bugs] [Bug 541130] [avimux] full and fast recording

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-good | Ver: HEAD CVS




------- Comment #4 from Mark Nauwelaerts  2008-07-04 21:46 UTC -------
If I use the pipeline I gave above, but with 720x576, I also experience
problems.  However, if I adjust to the following pipeline, I do not:

gst-launch-0.10 v4l2src queue-size=15 num-buffers=200 ! "video/x-raw-yuv,
format=(fourcc)YUY2, width=720, height=576,framerate=(fraction)25/1"  !  queue
! avimux name=mux \
alsasrc buffer-time=500000 provide-clock=1 num-buffers=56 blocksize=12000 !
"audio/x-raw-int, rate=48000, channels=1" ! queue ! mux. \
mux. ! filesink location=record.avi

The difference is in:
* queue-size has been set for v4l2src
* audio buffer size has been changed

and the explanation, I believe, is as follows:
* dumping a lot of (raw) data creates a lot of I/O activity, which keeps kernel
and/or PCI bus (somewhat more) occupied, so having a small queue along the way
(= the v4l2 capture buffer queue) could then be more painful than otherwise
(i.e. drops, irregular capture, ...)
* smaller audio buffers allow for better interleaving, otherwise players might
experience jerkyness, latency and/or complain "bad interleaving"

Even with the above issues addressed, there can still be the following effect
that might cause minor glitches, though likely not so pronounced (based on
test):
* whatever (video) does make it through is likely to have even more irregular
timestamps (than they otherwise already are), specifically without videorate or
so to straighten these out.  avimux then orders/muxes those accordingly (as it
should), which can then also lead to bad/irregular interleaving

But, as said, the pipeline given above already does a (near) impeccable job in
my case, and going to full tricks/techniques according to aforementioned URL,
it is likely even more so the case.


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