Very interesting. Something to keep in mind if we get involved with
video streaming!
Thanks.
Devendra.
Tim Roberts wrote:
AI Developer wrote:
Are you sure about that? Sounds like a bug in the renderer if it
expects a frame in paused state.
I am absolutely positive. This is a well-known strangeness in
DirectShow. You can check the DirectShow code in CBaseRenderer. It
will not complete the transition to "paused" state until it either
receives a frame, or gets an indication that the upstream filter cannot
deliver one.
For a KS source, that's done by setting
KSPIN_FLAG_PROCESS_IN_RUN_STATE_ONLY in the the Flags member of
KSPIN_DESCRIPTOR_EX:
http://msdn.microsoft.com/en-us/library/aa509735.aspx
For a user-mode filter, that's done by returning VFW_S_CANT_CUE from
IMediaFilter::GetState:
http://msdn.microsoft.com/en-us/library/ms783300.aspx
As I said, the renderer relies on this behavior to put up a pretty
"post" frame while the graph is still preparing. This was done because
of network latency. When you are streaming a video from a network
server somewhere, it makes a better user experience if you can display
the first frame of the movie while you pre-fetch enough frames for
smooth playback.
Seeing
Neetu's later comment about Cancel request handling, could it be
that in your case also, a cancel request is not being handled
correctly? Perhaps the render is waiting for the request to be
cancelled?
Not in the video case. I guarantee it.
As
for danger - yes there is a real danger. A lot of applications
submit buffers in pause state, so that the driver has a queue of
buffers ready when it switches to run state. Also, this way, the client
could ensure that there's going to be enough "backup" of buffers during
the time it takes to complete the request and to submit a new one.
Reduces chances of buffer underruns.
Yes, but you're talking about "steady state" operation here. The
operation at startup is kind of a corner case. On the other hand, you
have convinced me that I could not possibly have been correct for the
audio case. The video case is different.
And
of course, the WHQL tests will fail your driver (I know this as a
fact for audio drivers) if you try to stream in paused state!
Yes, it appears that I erred in attempting to extrapolate from the
video case to his audio behavior...
--
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
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