Our application uses the Sequence Grabber to record a single video
channel and a single audio channel to a single movie file. Every so
often (under the control of a separate part of the application), I
stop the SG, reconfigure the channel outputs to record to a different
movie file, and then start recording to this new file. This is
intended to be able to go on for a long time (e.g. multiple days).
In summary, there is an overall, long-term recording which is
composed of numerous, simple SG recording sessions.
Testing is revealing a frustratingly occasional and (at the
application level) inexplicable bug where the SG created movie file
is empty (technically, the file is not size zero, rather, around
100KB but there is no movie resource, it cannot be opened). Within
the application, the only time the SG returns an error during this
problematic portion of the overall recording is at the end when
SGStop returns -2014 (invalidDuration), which makes some sense as the
duration seems to be zero. Thus, the preexisting sequence grabber
and channels are used to create and apply a new output, start
recording, and, finally, the required repeated calls to SGIdle -- all
with no hint of an error, yet, we are left with an, essentially,
empty movie file.
So, after running our application you are sometimes left with an
overall recording which contains gaps in video content (i.e. empty
movie files). At the application level, we have no idea what is
going on and how to attempt to reduce/remove these gaps. The only
clue we have is that the frequency of empty movie files increases
when our application runs on a laptop vs. a desktop machine (perhaps
because of firewire bus performance??). Note: it is the case that,
besides the video camera, our application uses another device
connected via firewire whose data is written to a file in parallel to
the A/V data.
Up here at the top of the pile, I am left to guess what might be
going wrong. The Sequence Grabber abstracts all of the details away
which is a blessing and, for debugging, a curse. I ask You, the all-
knowing collective of QT people:
(1) Any debugging hints/tools I could use to gather more data about
this problem?
(2) What might be the cause of the problem? (solution?)
Mark Sanvitale
Electrical Geodesics, Inc.
email@hidden
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