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I'm trying to take snapshots with my Pi3 + USB camera. I've tried a few different things, but all with different results. I've tried:

  mplayer -vo jpeg -frames 1 tv://

And the output text is:


MPlayer2 2.0-728-g2c378c7-4build1 (C) 2000-2012 MPlayer Team
Cannot open file '/home/jems/.mplayer/input.conf': No such file or directory
Failed to open /home/jems/.mplayer/input.conf.

Playing tv://.
Detected file format: TV
Selected driver: v4l2
 name: Video 4 Linux 2 input
 author: Martin Olschewski 
 comment: first try, more to come ;-)
v4l2: your device driver does not support VIDIOC_G_STD ioctl, VIDIOC_G_PARM was used instead.
Selected device: UVC Camera (046d:0990)
 Capabilities:  video capture  streaming
 supported norms:
 inputs: 0 = Camera 1;
 Current input: 0
 Current format: MJPEG
tv.c: norm_from_string(pal): Bogus norm parameter, setting default.
v4l2: ioctl enum norm failed: Inappropriate ioctl for device
Error: Cannot set norm!
Selected input hasn't got a tuner!
v4l2: ioctl set mute failed: Invalid argument
v4l2: ioctl query control failed: Invalid argument
jpeg: Progressive JPEG disabled.
jpeg: Baseline JPEG enabled.
Opening video filter: [scale]
[ass] auto-open
Selected video codec: MJPEG (Motion JPEG) [libavcodec]
Audio: no sound
Starting playback...
v4l2: select timeout
[mjpeg @ 0x76186870]No JPEG data found in image
Error while decoding frame!
[mjpeg @ 0x76186870]No JPEG data found in image
Error while decoding frame!
v4l2: select timeout
[mjpeg @ 0x76186870]No JPEG data found in image
Error while decoding frame!
[mjpeg @ 0x76186870]Changeing bps to 8
VIDEO:  640x480  15.000 fps    0.0 kbps ( 0.0 kB/s)
[swscaler @ 0x7587a488]bicubic scaler, from yuv420p to rgb24 using C
[swscaler @ 0x7587a488]No accelerated colorspace conversion found from yuv420p to rgb24.
[swscaler @ 0x7587a488]using unscaled yuv420p -> rgb24 special converter
VO: [jpeg] 640x480 => 640x480 RGB 24-bit 
jpeg: . - Output directory already exists and is writable.
V:   0.0   4/  4 ??% ??% ??,?% 0 0 

v4l2: ioctl set mute failed: Invalid argument
v4l2: 3 frames successfully processed, 0 frames dropped.

Exiting... (End of file)
$

It works, and creates and image, but the image color is all blue and red:

enter image description here

Also, if I try to run the command again, I get no image and the following output:

$ mplayer -vo jpeg -frames 1 tv://
MPlayer2 2.0-728-g2c378c7-4build1 (C) 2000-2012 MPlayer Team
Cannot open file '/home/jems/.mplayer/input.conf': No such file or directory
Failed to open /home/jems/.mplayer/input.conf.

Playing tv://.
Detected file format: TV
Selected driver: v4l2
 name: Video 4 Linux 2 input
 author: Martin Olschewski 
 comment: first try, more to come ;-)
v4l2: your device driver does not support VIDIOC_G_STD ioctl, VIDIOC_G_PARM was used instead.
Selected device: UVC Camera (046d:0990)
 Capabilities:  video capture  streaming
 supported norms:
 inputs: 0 = Camera 1;
 Current input: 0
 Current format: MJPEG
v4l2: ioctl set format failed: Input/output error
v4l2: ioctl set mute failed: Invalid argument
v4l2: 0 frames successfully processed, 0 frames dropped.
Opening as detected format "TV" failed.
Failed to recognize file format.


Exiting... (End of file)

So I tried using ffmpeg, as follows:

ffmpeg -i /dev/video0 -vframes 1 output.png

Which created a smaller picture, but it worked:

enter image description here

However, I can only run either command once. If I try again, I get an error:

/dev/video0: Input/output error

And I have to reboot in order to take another picture.

Does anyone have a solution which works consistently? The first command I mentioned works well on my Linux Mint desktop every time, so I don't think there is a problem with my camera.

Thanks!

Jessica 6
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  • Not exactly ideal, but you could try just resetting the USB port after each image capture, rather than rebooting. – goobering Mar 23 '16 at 20:20
  • In regards to your "there is no problem with my camera" assumption. The drivers used on the RPi and your desktop are likely different - causing these issues. So, even if your camera (through its drivers) works on your desktop, it could be a problem related the driver you are using on the RPi – Chris Mar 24 '16 at 04:32

2 Answers2

5

Does fswebcam could work for you ?

Install it with:

sudo apt-get install fswebcam

Basic usage:

fswebcam image.jpg

Specific resolution:

fswebcam -r 1280x720 image2.jpg

Otherwise you could use OpenCV and write a small C/C++ program which use:

 cvQueryFrame(cap);
 cvSameImage(filename, frame, params);

See OpenCV API for example.

ssinfod
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  • Ok, this works better! But again, after 1 or 2 captures, it will fail to work. The output I get:Trying source module v4l2... /dev/video0 opened. No input was specified, using the first. But I could some code to 'reset the usb device', which works. So, I guess I kinda have a solution with a reset script. Thanks! – Jessica 6 Mar 24 '16 at 00:53
  • Maybe try a python script with OpenCV code as suggested and let us know if that works - would be interesting for me to hear. – Chris Mar 24 '16 at 04:28
  • Here is a very short intro to using fswebcam: https://www.youtube.com/watch?v=JnQh-o9aSD0 – SDsolar Jun 17 '18 at 06:57
1

Most of your examples try to make use of the Video4Linux2 driver. A USB camera should work with this API with no problem. Check that the tools for this are correctly installed:

sudo apt-get install v4l-utils

I know you are using a USB camera but just for other people's benefit, if you use the RPI camera interface you have to load the BCM driver:

sudo modprobe bcm2835-v4l2

Then you can access the camera device which is at /dev/videoN where N is normally 0 if there is only one camera.

You can check all the information about video devices using

v4l2-ctl --all

or more specific modes available using

v4l2-ctl --device=/dev/video0 --list-formats-ext

These commands should show you if there are general errors using this driver to access information about the camera. You can get the driver information by typing

v4l2-ctl -D

You can even capture a jpeg with:

v4l2-ctl --set-fmt-video=width=2592,height=1944,pixelformat=3
v4l2-ctl --stream-mmap=3 --stream-count=1 --stream-to=somefile.jpg

You might have to set the correct width and height parameters for your camera.

Robotbugs
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