Consistently getting 7.5fps using examples about libv4l-rs

[raymanfx]

What kind of camera are you using?
Please add the active format and parameters you are using. Also, are you running a release or debug mode build?

[mijoharas]

Hey, I'm using a pretty standard laptop webcam (goes up to 720p, and with MJPEG it'll do 30FPS, slightly lower on YUYV).
I've tried both release and debug.
I messed around with a few different formats (and shrinking it right down to eliminate a slow processor or something as an issue).

Here is some output from a couple of frames of stream_capture_mmap:

Using device: /dev/video0

Active format:
width          : 320
height         : 180
fourcc         : YUYV
field          : progressive
stride         : 640
size           : 115200
colorspace     : sRGB
quantization   : default
transfer       : default transfer function

Active parameters:
capabilities : TIME_PER_FRAME
modes        : (empty)
interval     : 1/30 [s]

Buffer
  sequence  : 2
  timestamp : 1665.073533 [s]
  flags     : MAPPED | TIMESTAMP_MONOTONIC | TSTAMP_SRC_SOE
  length    : 115200
Buffer
  sequence  : 3
  timestamp : 1665.205535 [s]
  flags     : MAPPED | TIMESTAMP_MONOTONIC | TSTAMP_SRC_SOE
  length    : 115200

FPS: 7.462410290914528
MB/s: 0.8201908832008339

Also, for info here is the formats supported from v4l2-ctl:

v4l2-ctl --list-formats-ext
ioctl: VIDIOC_ENUM_FMT
	Type: Video Capture

	[0]: 'YUYV' (YUYV 4:2:2)
		Size: Discrete 640x480
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 960x540
			Interval: Discrete 0.067s (15.000 fps)
		Size: Discrete 848x480
			Interval: Discrete 0.050s (20.000 fps)
		Size: Discrete 640x360
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 424x240
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 352x288
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 320x240
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 320x180
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 1280x720
			Interval: Discrete 0.100s (10.000 fps)
	[1]: 'MJPG' (Motion-JPEG, compressed)
		Size: Discrete 640x480
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 960x540
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 848x480
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 640x360
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 424x240
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 352x288
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 320x240
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 320x180
			Interval: Discrete 0.033s (30.000 fps)
		Size: Discrete 1280x720
			Interval: Discrete 0.033s (30.000 fps)

[mijoharas]

Also, one thing to note, it seems to be consistently very close to 7.5 FPS. it's not a rough number, and it's never been anything else during my testing. (I can't fully remember what it was when I was testing the other day, but wouldn't be surprised if it was the same).

[raymanfx]

I'm afraid I can't reproduce this using my Logitech C922 Pro Stream - I'm getting consistent 30 FPS in MJPG or 20-30 in YUYV. What kind of frame times are you getting when using v4l2-ctl for mmap streaming?

[mijoharas]

Oh wow... this is strange...:

time v4l2-ctl --device /dev/video0 --stream-mmap --stream-to=frame.raw --stream-count=100                                                                                                                                                         
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.15 fps, dropped buffers: 1
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.14 fps
<<<<<<<<<<<<<<<<<< 26.12 fps
<<<<<<<<<<< 22.37 fps
<<<<<<<< 19.25 fps

I then Ctrl+C-ed it, and did it again afterwards:

 time v4l2-ctl --device /dev/video0 --stream-mmap --stream-to=frame.raw --stream-count=1000
 <<<<<<<< 7.52 fps, dropped buffers: 1
<<<<<<<< 7.50 fps
<<<<<<< 7.51 fps
<<<<<<< 7.50 fps
<<<<<<<< 7.50 fps
<<<<<<< 7.50 fps

I wonder what could be causing this...

Thanks for your help. I guess I'll close this issue, as it doesn't seem to be to do with this library.

If you have any ideas for places I could look do let me know, but I'll dig into this by myself.

(and thanks for the tip, didn't realise you could stream directly from v4l2-ctl).

[mijoharas]

oh wow... I figured it out, that was quick https://stackoverflow.com/questions/46228379/v4l2-framerate-drops

moving to a brighter room sorts it out. Sorry for the distraction!

time v4l2-ctl --device /dev/video0 --stream-mmap --stream-to=frame.raw --stream-count=1000                                                                                                                                             INT ↵  5s    default 🐍  2.6.3   
<<<<<<<< 7.52 fps, dropped buffers: 1
<<<<<<<<<<<<<< 10.83 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 17.17 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 20.36 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 22.29 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 23.59 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 24.50 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 25.20 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 25.73 fps
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 30.08 fps

[mijoharas]

that explains why the framerate seems to drop when I code at night 😄

[raymanfx]

Oh sorry, I could have saved you some time there :D
Most, if not all, laptop cameras are really garbage products and way too sensitive to changing light conditions.