AW: Slow Memory Access in AppSink

[Thornton, Keith]

Hi,
try asking if the buffer is writable (gst_buffer_is_writable). If it is not writeable, calling gst_buffer_map(GST_MAP_WRITE) will presumably make a copy if the reference count on the buffer is > 1. It is probably the copying of the data which takes so long.
With GST_MAP_READ you do the copy manually which would take the same amount of time. This is the same if you copy the data into a pre-allocated buffer.
Gruesse

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Von: gstreamer-devel <gstreamer-devel-bounces at lists.freedesktop.org> Im Auftrag von Kazanian
Gesendet: Dienstag, 1. September 2020 09:44
An: gstreamer-devel at lists.freedesktop.org
Betreff: Slow Memory Access in AppSink

Hi,

I'm working with an  NXP i.MX8M and I have built a GStreamer-pipeline where I decode a H264-stream and put the data in an appsink. In the appsink-callback-function, I do some resorting of all pixels to get it in a different format. The pipeline looks like this:
H264-file -> h264parse -> vpudec -> appsink -> resorting algorithm

It works so far, but to get memory access to the frame buffer in the callback-function, I use the function gst_buffer_map with the flag GST_MAP_WRITE and it takes too much time. For a 1920x1080 video frame, it takes 34 ms and then the resorting algorithm takes 5 ms.  If I use GST_MAP_READ instead, the map function is fast (0.02 ms), but then the resorting algorithm takes much longer. Probably because the data has to be fetched from some other memory.
What exactly is the reason for this? What can I do to make the mapping faster?

My idea to solve this was to allocate a few buffers before starting the pipeline and call gst_buffer_map with flag GST_MAP_WRITE on these buffers beforehand and let the gstreamer use these pre-allocated buffers. But I have not found a way to tell gstreamer to write the decoded data into these buffers? Is there a way to do this?

Thanks for any advice!



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