[gst-devel] rate change not very responsive

[Jan Schmidt]

On Mon, 2009-01-19 at 14:48 +0100, arturo castro wrote:
> Hi
> 
> I'm one of the developers of the openframeworks project:
> http://openframeworks.cc , a framework for creative coding. Since now
> we've been using some object oriented wrapper around FFMPEG as our video
> backend in the linux version but it's being problematic and super slow
> so i've decided to give gstreamer a try.
> 
> With the new version of appsink in base everything has gone more or less
> smooth except for one little problem. When i try to change a video
> playing speed from a gui control like a slider or just mapping that
> property to the mouse position, the video stops playing while speed is
> changing and only continues playing again when speed stops changing.
> 
> I'm using a pipeline like:
> 
> filesrc location=... ! decodebin ! ffmpegcolorspace ! appsink
> 
> also using signals in appsink to notify new buffers and polling the
> pipeline for messages with:
> 
> while(gst_bus_have_pending(bus)){
>    GstMessage* msg = gst_bus_pop(bus);
>    ...
> 
> as i cannot get callbacks from the bus since i cannot run in the
> gstreamer loop because our framework already has it's own.
> 
> I've tried with diferent seek flags but have more or less the same
> result.
> 
> This is the code i'm using to change speed directly mapped to gui
> control:
> 
> void ofVideoPlayer::setSpeed(speed)
>     GstFormat format = GST_FORMAT_TIME;
>     GstSeekFlags flags = (GstSeekFlags) (GST_SEEK_FLAG_FLUSH|GST_SEEK_FLAG_ACCURATE);
> 
>     if(!gst_element_seek(GST_ELEMENT(gstPipeline),speed, format,
> 			flags,
> 			GST_SEEK_TYPE_NONE,
> 			0,
> 			GST_SEEK_TYPE_NONE,
> 			-1)) {
> 			ofLog(OF_WARNING,"GStreamer: unable to seek");
>    }
> }
> 
> 
> also attached is the full code for our videoPlayer class. 
> 
> Is there anything i can do to make speed change more responsive, or is
> this just a limitation of the current implementation of gstreamer?
> 

How responsive it's going to be is a function of the pipeline mostly.
You might want to check out the 'scrubby' example in
gst-plugins-base/tests/examples/seek/scrubby.c - it does pretty much
what you're looking for.

There has been some discussion of how we might perform
rate-changes-that-don't-change-the-playback-direction more quickly, but
nothing has come of that yet.

J.

-- 
Jan Schmidt <thaytan at noraisin.net>