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Camera framerate is not fixed. #233

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Williangalvani opened this issue Mar 20, 2019 · 4 comments

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@Williangalvani
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commented Mar 20, 2019

The issue was previously open in bluerobotics/qgroundcontrol#217.

Discussion was started here.

The framerate can be checked by playing the video with this gstreamer pipeline:

gst-launch-1.0 -v udpsrc port=5600 caps='application/x-rtp, media=(string)video, clock-rate=(int)90000, encoding-name=(string)H264' \
! rtph264depay \
! avdec_h264 \
! videoconvert \
! fpsdisplaysink

I was unable to make it fixed by playing with the camera settings.
Also while increasing exposure time gives us a low framerate, I was unable to get 30fps even with manual minimum exposure.

@jaxxzer

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commented Mar 20, 2019

I think we should get some sort of live statistics in QGC and/or companion in order to explore this more under various conditions and with different cameras.

@Williangalvani

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commented May 17, 2019

I think a good test will be using a simple pipeline. I suspect some uv4l settings are probably to blame

@quattrinili

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commented May 17, 2019

Although in the video that I attached in the BlueRobotics forum I did not a good job on keeping the camera with the same field of view, I thought that I tried under same conditions over the repetitions of the same experiments, but apparently not.

I did another test with the spare camera I have, and indeed, it is the auto exposure that does not constrain the maximum exposure time according to the framerate set.

In particular, the experiment involves camera without any obstruction, and camera with my hands covering the field of view to make it darker, and indeed the framerate drops, when the auto exposure is set to the default value which according to the get command of v4l2-ctl is 3. Setting the auto exposure to false through this command
v4l2-ctl --set-ctrl=exposure_auto=1 works. Note that this was tested with the exposure left to the default (156)

And just to test this hypothesis, I also tried to change exposure_absolute, if we set it to the maximum, it dropx to 1fps, if we set it to the minimum clearly it works. Experimentally, it seems that the value where the dropping of the frames starts is around 310. If I have time I will plot the dropping.

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