Hi, gstreamer-devel:     Thanks, Arnout! I got it. Eric Zhang <div class="gmail_quote">2008/11/10 Arnout Vandecappelle <<a href="mailto:arnout@mind.be">arnout@mind.be</a>> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="Ih2E3d">On Monday 10 November 2008 03:58:18 Eric Zhang wrote: >     So could you explain a little bit why we should add this extra > capsfilter to make decodebin works? Thanks a lot. </div> If you think a bit about it, it's easy enough to understand.  gst-launch is completely agnostic about what all the pipeline elements do, but it somehow has to choose which sink pad to connect to which source pad of the rtspsrc. Look at the gst-launch command: <div class="Ih2E3d"> gst-launch rtspsrc location="rtsp://xxxxxx" name=d  d. ! decodebin ! ffmpegcolorspace ! xvimagesink  d. ! decodebin ! audioconvert ! alsasink </div>When rtspsrc creates a video source pad, gst-launch has to choose which of the two decodebins to connect to it.  Since they look identical (gst-launch can't look into the rest of the pipeline, who knows what decodebin will do anyway?), gst-launch randomly connect the video source to one of the decodebins.  After prerolling, the decodebin creates a source pad for the video and gst-launch has to connect it to the next element.  Now, if you're lucky, gst-launch had select the first decodebin and all goes well.  If you're unlucky, however, it has chosen the second decodebin, and gst-launch connects the audioconvert to the decodebin's video source pad...  That doesn't work, so the linking fails.  That doesn't crash your application yet.  It's only when the pipeline goes into PLAYING and the source starts pushing data in the decodebin, that it turns out that the decodebin doesn't have anywhere to send the data to. That's what triggers the 'Not linked' error.  When you use the depayloader and decoder explicitly instead of decodebin, the linking works correctly: <div class="Ih2E3d"> gst-launch rtspsrc location="rtsp://xxxxxx" name=d  d. ! rtph263pdepay ! ffdec_h263 ! ffmpegcolorspace ! xvimagesink  d. ! rtpamrdepay ! amrnbdec ! audioconvert ! alsasink </div>Now, the two branches of the pipeline are no longer identical.  gst-launch looks at the caps of rtph263pdepay and rtpamrdepay to see which one matches the video source.  It will therefore always select the right one.  You get the same behaviour with a decodebin by providing caps explicitly.  Regards,  Arnout -- Arnout Vandecappelle                               arnout at mind be Senior Embedded Software Architect                 +32-16-286540 Essensium/Mind                                     <a href="http://www.mind.be" target="_blank">http://www.mind.be</a> G.Geenslaan 9, 3001 Leuven, Belgium                BE 872 984 063 RPR Leuven LinkedIn profile: <a href="http://www.linkedin.com/in/arnoutvandecappelle" target="_blank">http://www.linkedin.com/in/arnoutvandecappelle</a> GPG fingerprint:  D206 D44B 5155 DF98 550D  3F2A 2213 88AA A1C7 C933 <div><div></div><div class="Wj3C7c"> ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world <a href="http://moblin-contest.org/redirect.php?banner_id=100&url=/" target="_blank">http://moblin-contest.org/redirect.php?banner_id=100&url=/</a> _______________________________________________ gstreamer-devel mailing list <a href="mailto:gstreamer-devel@lists.sourceforge.net">gstreamer-devel@lists.sourceforge.net</a> <a href="https://lists.sourceforge.net/lists/listinfo/gstreamer-devel" target="_blank">https://lists.sourceforge.net/lists/listinfo/gstreamer-devel</a> </div></div></blockquote></div>