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Hi all,</div>
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I am trying to get a GStreamer application working where the upstream element (an appsink) will be able to pass a custom buffer pool into an avdec_mjpeg decoder. The reason for doing this is to avoid a memcpy() operation between the avdec_mjpeg decode and
the display. This implementation is an embedded system with limited resources (it is an FPGA SoC, Xilinx Zynq) and so avoiding a memcpy is essential to maintaining performance.</div>
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In the ideal world, I would implement a custom allocator that when presented with a request for a new buffer would choose one of the N buffers available in FPGA space. (N ~14 at present, could be extended later.) Or I could set up a bufferpool with all these
buffers available. The buffer addresses are fixed: they are mmap'd representations of physical addresses, so unfortunately I can't do this any other way (unless I write my own JPEG decoder, which I'm trying to avoid doing.)</div>
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In the ideal world, the JPEG decode would directly decompress the pixel data into the passed framebuffer, achieving zero-copy performance. </div>
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The problem I'm having is I've tried setting up an ALLOCATION query like so:</div>
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gst_element_foreach_sink_pad(GST_ELEMENT(gAppSink), cb_padForeach, NULL);</div>
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then my <span style="background-color:rgb(255,255,255); display:inline!important">cb_padForeach implementation is like this:</span></div>
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<span style="background-color:rgb(255,255,255); display:inline!important"><br>
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<span style="background-color:rgb(255,255,255); display:inline!important">
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gboolean cb_padForeach(GstElement *element, GstPad *pad, gpointer user_data)
<div> {</div>
<div> printf("pad %08x %08x %08x\n", element, pad, user_data);</div>
<div><br>
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<div> GstCaps *resultCaps = gst_caps_new_empty_simple("result");</div>
<div> GstCaps *caps = gst_caps_new_empty_simple("mycaps");</div>
<div> gboolean need_pool = FALSE;</div>
<div> </div>
<div> GstQuery *query = gst_query_new_allocation(caps, TRUE);</div>
<div> gst_pad_query(pad, query);</div>
<div><br>
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<div> gst_query_parse_allocation(query, &resultCaps, &need_pool);</div>
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<div> GstBufferPool *pool = gst_buffer_pool_new();</div>
<div> gst_buffer_pool_config_set_params(GST_STRUCTURE(pool), NULL, 460800, 36, 36);</div>
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<div> gst_query_add_allocation_pool(query, pool, 460800, 36, 36);</div>
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<div> gst_caps_unref(caps);</div>
<div> gst_caps_unref(resultCaps);</div>
<div><br>
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<div> return TRUE;</div>
}<br>
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It may be obvious, but I don't *really* know what I'm doing here; I'm trying to set the bufferpool up for now to have 36 qty of buffers each 460800 bytes long, but avdec_mjpeg is still using its two buffers (I can see if I print the buffer addresses going
into appsink.) I know this block is entered, but it doesn't appear to influence any behaviour in GStreamer. <span style="background-color:rgb(255, 255, 255);display:inline !important">N.B. I use 36 in this example as I saw some code in the avdec_X plugin
that suggested it wanted to see at least 32 buffers in its ALLOCATION query, but I'm unclear as to whether that is encountered here. I just set it high for now so I could ensure I wasn't trapping on this. And I'm aware that this is not using my FPGA buffer
addresses, but one step at a time!</span></div>
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<span style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">I'd appreciate pointers (no pun intended) to any examples of setting up custom bufferpools or allocators in the upstream.
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This is my pipeline (in gstreamer syntax, the implementation is in C):</div>
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udpsrc port=5555 ! 'application/x-rtp,payload=26' ! rtpjpegdepay ! queue ! jpegparse ! avdec_mjpeg ! videoconvert ! appsink</div>
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I know this pipeline works ok as I can replace appsink with a display sink and I see video from my test pattern generator, also running with GStreamer. </div>
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[P.S. I had posted this on IRC, but as I was using a web-client I lost any chat history, and I've just moved house so I've been offline for a week, so apologies if I'm repeating myself.]</div>
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Thanks in advance for any advice,</div>
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Tom </div>
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