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<p class="MsoNormal">Thanks a lot for your reply,</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have been able to adjust the pool size using a pad probe reply to the Allocation query.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Note that I needed to set the probe on a pad of either v4l2src or capsfilter. I could not make it work if I set the probe on the appsink pad (maybe because of probe replies aggregation in the tee element, I did not investigate further).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Side note:<o:p></o:p></p>
<p class="MsoNormal">I also noted that setting the v4l2src buffer pool size changed the way the v4l2src element behaves when there are no more buffer available (because they are all in the downstream elements):<o:p></o:p></p>
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<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1">Without any explicit buffer pool size, the count is set to a small value (4). If there is a need for more buffers, new buffers are allocated and data is copied in those. Capture can
continue to operate, at the cost of more memory management and memory copies.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1">With an explicit buffer pool size, if all the buffers of the pool are in use, then the V4L2 driver is not provided with any buffer to capture the images. Capture will then completely
stop.<o:p></o:p></li></ul>
<p class="MsoNormal">It is therefore very important to set the buffer pool count large enough.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Hi,<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">We are working on an application where the pipeline is configured as follow:<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">v4l2src ! capsfilter caps=[…] ! tee name=t ! appsink ! t. [remaining of pipeline not important for this discussion]<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">The v4l2src video source uses DMABUF acquisition, which is great to reduce memory copies.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">However, to completely prevent memory copies, the buffer pool in v4l2src should have enough buffers available for the v4l2 driver while acquired buffers are sent to the downstream
elements.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">If I understand correctly, the number of buffers in the v4l2src buffer pool is decided (amongst other things) according to the GST_QUERY_ALLOCATION query response to the downstream
elements. The downstream elements could inform the upstream v4l2src of their needs (for example, if they need to keep references to the acquired buffers).<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Here is where things get complicated: our application keeps references on many buffers sent to the app via appsink. The application needs to have some short time history of the
buffers. We allowed the app to keep references to a fixed number of buffers. As far as I investigated, there seems to be no way for the appsink to inform the upstream elements (v4l2src) about this fact, via GST_QUERY_ALLOCATION reply or via other means.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">My question:<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">What is the best way to configure the v4l2src to allocate a pool with a larger number of buffers?<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Is it possible via a reply to GST_QUERY_ALLOCATION from the downstream appsink (or other)?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">You can and should implement the allocation query using a pad probe. You probably want to expose the videometa support, and set a minimum number of buffers, be aware that the pool pointer can be left to null. Have a look at kmscube software
for some examples (only the meta though).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Is there a hidden way to configure the v42lsrc buffer pool size directly?<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Thanks<o:p></o:p></p>
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