I don't know how your pipeline is, but when I did crossfading I achieved this by the caps properties. Even it fits for 2 video files I think the principle is the same. Here's the thread: <a href="http://gstreamer-devel.966125.n4.nabble.com/crossfading-audio-error-gst-mad-chain-mad-header-decode-had-an-error-lost-synchronization-td4037851.html#a4037881">http://gstreamer-devel.966125.n4.nabble.com/crossfading-audio-error-gst-mad-chain-mad-header-decode-had-an-error-lost-synchronization-td4037851.html#a4037881</a> Basically I did 2 gnlcomposition, one for audio and another for video. Sorry I don't have the pipeline in this computer. But it was something like this. <a href="http://gstreamer-devel.966125.n4.nabble.com/No-sound-in-my-pipeline-td3854506.html">http://gstreamer-devel.966125.n4.nabble.com/No-sound-in-my-pipeline-td3854506.html</a> Hope it helps. Rossana <div class="gmail_quote">2012/1/17 Ralph <<a href="mailto:ralph.gucwa@racelogic.co.uk">ralph.gucwa@racelogic.co.uk</a>> <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> I'm using gnonlin to play a sequence of video file fragments. I constructed a pipeline containing two gnlcomposition objects - one for video and the other for audio, they are playing the same video files. In order to be able to have gaps between the files, I created videotestsrc and audiotestsrc and added them through gnlsources (priority: uint.MaxValue) to gnlcomposition objects. My "timeline" looks like this: 659.24s file, start position 2s (2s gap before the file) 881.04s file, start position 661.24s (4s gap before the file) When I disable the audio part, the video works nicely - the file fragments are played exactly when scheduled and the gaps between them are precisely the required length. Perfect! The problems occur when I enable the audio section - the gaps become much shorter, strange things start to happen. When I try to play both video and audio, the first file begins after just 0.4s, and when it ends, the video skips the second gap and jumps many seconds into the second file and the video remains frozen, it waits for the audio (which is playing nicely except for the 1.6 second shorter gap) to that position and then continues. What's interesting the length of the initial gap is always 1.6 seconds shorter than it should be - when the gap should be 20s, it is played within 18.4 seconds. The second gap is always completely wrong. It's not the problem with the video, if I disable the video section, the audio is wrong, the gaps are shorter than scheduled. What's wrong with my pipeline? My video files are: video: Xvid ISO MPEG-4 720x576 25fps audio: MPEG-1 Layer 2 48kHz 192kb/s stereo The audio gnlcomposition runs at 48kHz, the audio is then converted using audioconvert. The audiotestsrc runs at 44.1kHz. The autoaudiosink runs at 44.1kHz. -- View this message in context: <a href="http://gstreamer-devel.966125.n4.nabble.com/Synchronising-audio-and-video-in-gnonlin-tp4303968p4303968.html" target="_blank">http://gstreamer-devel.966125.n4.nabble.com/Synchronising-audio-and-video-in-gnonlin-tp4303968p4303968.html</a> Sent from the GStreamer-devel mailing list archive at Nabble.com. _______________________________________________ gstreamer-devel mailing list <a href="mailto:gstreamer-devel@lists.freedesktop.org">gstreamer-devel@lists.freedesktop.org</a> <a href="http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel" target="_blank">http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel</a> </blockquote></div>