Dears, I found the reason why my buffer_alloc() is not called. So I answer this question by myself and for your reference if some body needs it. At first, I used the udpsrc as my source, but udpsrc malloc the buffer itself, and doesn't use gst_pad_alloc_buffer(). gst_pad_alloc_buffer() will invoke the sink's buffer_alloc() function. It is independent of pull-mode or push-mode. The source, videotestsrc, is an example to use gst_pad_alloc_buffer(). France Hsu <div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Hi! Tim, Thanks for your reply. I would misunderstand the meaning of "pull-mode sink". You mean, pull-mode and buffer allocated by sink are two different things, right? In the fact, my sink is for a HW device, so I want the source to use the HW buffer (allocated in sink) for data flow, not to allocate by source itself. I wish to use udpsrc for the pipeline, and found it is based on GstPushSrc. (Therefore, I thought I should implement a pull-based sink, and find a pull-based source) $ gst-launch udpsrc udp://IP:PORT ! mysink However, my buffer_alloc function is not called. France Hsu > Hi, > > > I'm a newbie for gstreamer and working on a sink that I wish it would > > provide buffer for source. I think it would be a pull-based sink. > > (...) > > I implemented this sink based on base-sink, and added the virtual > > function: buffer_alloc() (gst_my_sink_buffer_alloc) and render() > > (gst_my_sink_render). > > What kind of sink is this? > > There's no need for the sink to operate in pull mode to be able to > provide buffers to upstream. It should be sufficient to implement a > buffer alloc function. > > Take for example: > > $ GST_DEBUG=*src:5,*sink:5 videotestsrc num-buffers=2 ! ximagesink > > This will operate in push mode, but videotestsrc will call > gst_pad_alloc_buffer() to get a buffer from ximagesink and then fill > that with data and push it back to ximagesink. > > Pull mode for sinks is something that's not really used much in practice > and is rarely useful. Maybe you could provide some more details of what > you're trying to do? > > Cheers > -Tim > > </blockquote></div>