play multiple sources at once, each from a different position

[Nicolas Dufresne]

Le samedi 29 janvier 2022 à 00:30 +0100, Tomasz Mikolajczyk a écrit :
> Thank you. Could you tell if something like that is doable in gstreamer
> itself?  If yes, could you explain here how to achieve it? I just need to play
> two sources together but both starting with different offset. Thank you in
> advance.

GES is implemented using GStreamer, so the answer is yes. You can read GES code,
specially the NLE set of GstElement if you need to learn how this is done. It is
non-trivial though, hence why there is a library with elements to solve this.

> 
> On Tue, Jan 25, 2022 at 4:55 PM Nicolas Dufresne <nicolas at ndufresne.ca> wrote:
> > Le lundi 24 janvier 2022 à 02:18 +0100, Tomasz Mikolajczyk via gstreamer-
> > devel a écrit :
> > > Hi,
> > > 
> > > I would like to use gstreamer to play multiple sources (for instance two
> > > video files) simultaneously using a single pipeline but each video
> > > starting from a different position, for instance first video from the
> > > beginning and the second from the middle. Could someone guide me on how to
> > > achieve it? 
> > > Simplifying, my pipeline is an equivalent of:
> > 
> > 
> > This use case is better handled by GES, which offers ges-launch-1.0 command
> > line to test.
> > 
> > https://gstreamer.freedesktop.org/documentation/gst-editing-services/?gi-language=c
> > 
> > > gst-launch-1.0 \
> > > uridecodebin
> > > uri=file:///Users/tmikolaj/Downloads/videoalpha_video_dancer1.webm !
> > > videoconvert ! autovideosink \
> > > uridecodebin
> > > uri=file:///Users/tmikolaj/Downloads/videoalpha_video_dancer1.webm !
> > > videoconvert ! autovideosink
> > > 
> > > , but created programmatically.
> > > Obviously, a simple pipeline's seeking seeks two files at once.
> > > I was trying to register a probe of the GST_PAD_PROBE_TYPE_EVENT_UPSTREAM
> > > type from inside the "pad-added" signal callback of the "uridecodebin"
> > > element. Inside the probe I wanted to catch the "GST_EVENT_SEEK" event and
> > > drop it for the first video. However, it seems that dropping the SEEK
> > > message leaves the pipeline in a "PAUSED" state and even an explicit state
> > > change to "PLAYING" does nothing.
> > > Does anybody have some hints on how to solve that problem?
> > > Regards,
> > > Tomasz
> > 
> >