Hi,
I would like to use 3 webcams. it’s works well with 2, but when I initialized 3 webcams
my application crash. Maybe be an usb bandwidth problem ?
the formats supported by my webcams :
Index : 0
Type : Video Capture
Pixel Format: ‘YUYV’
Name : YUV 4:2:2 (YUYV)
Index : 1
Type : Video Capture
Pixel Format: ‘MJPG’ (compressed)
Name : MJPEG
I would like to know if it’s possible to grab the “compressed” format ?
or if it’s not the problem ?
thanks in advance
it should work but never had the chance to test one, perhaps the easiest is to open that camera alone without the other 2 and see if it still crashes
I am trying to set a custom pipeline:
setPipeline("v4l2src name=video_source device=/dev/video1 ! video/x-raw,format=RGB,width=320,height=240,framerate=15/1 ", 24,false,320,240);
but I have the same probleme (it’s crash with 3)… how my cameras support “mjpg” I don’t know if it’s possible to change “video/x-raw” to get compressed image and get down the usb bandwidth?
yes, the videoplayer will always try to use a non compressed format to avoid the extra cpu usage from decompressing but something like:
setPipeline("v4l2src name=video_source device=/dev/video1 ! video/mpeg,width=320,height=240,framerate=15/1 ! decodebin ! videoconvert",24,false,320,240);
should work. i doubt though that at 320,240 the bandwidth is the problem. the bandwdth of 3 320x240 is around 10Mb/s while an HD stream at 30fps which usb2 is perfectly able to do is around 80Mb/s
About your pipeline I get nothing but no error, gst.isFrameNew() return false.
I think also that the problem about bandwidth it’s weird but I found this topic about opencv: http://stackoverflow.com/questions/9781770/capturing-multiple-webcams-uvcvideo-with-opencv-on-linux
"I had this exact problem, using three logitech quickcam pro 9000
cameras (using ubuntu). I could read from two, but not three. In my
case, I wasn’t using opencv, but was accessing the cameras through V4L2
directly, using memory-mapped IO. Simply put, there was not enough USB
bandwidth to allocate three buffers.
I was reading in the uncompressed frames, however. As soon as I
switched the format to MJPEG, the data was small enough, and I could
read from the three cameras. I used libjpeg to decode the MJPEG stream.
I haven’t looked into how to change the image format using OpenCV, but I do know that it needs to be MJPEG to fit all that data.
Before I switched to MJPEG, I spent a lot of time trying to access
each camera one at a time, streaming a single frame before switching to
the next. Not recommended!"
I noticed that the application run with 3 webcams all of times, the first run after the reboot of ubuntu but the second run ubuntu freeze and I have to stop the machin.
it’s maybe the vidGrabber which didn’t close properly ?
I have find the pipeline to get compressed image with my webcam:
gst[0]->setPipeline(“v4l2src name=video_source device=/dev/video0 ! image/jpeg,width=320,height=240,framerate=15/1 ! decodebin ! videoconvert”, 24,false,320,240);
I have less crash with this code:
the last webcam is start with the keyboard
and I have add sleep but this version still instable.
and when I close the application I have messages of error:
“GStreamer-CRITICAL **: gst_mini_object_unref: assertion ‘mini_object-> refcount > 0’ failed”
the code:
#include "ofApp.h"
//--------------------------------------------------------------
void ofApp::setup(){
test.allocate(320,240);
test2.allocate(320,240);
test3.allocate(320,240);
gst[0]= new ofGstVideoUtils();
gst[1]= new ofGstVideoUtils();
gst[2]= new ofGstVideoUtils();
//v4l2-ctl --set-fmt-video=width=320,height=240,pixelformat=1 -d /dev/video0
gst[0]->setPipeline("v4l2src name=video_source device=/dev/video0 ! image/jpeg,width=320,height=240,framerate=15/1 ! decodebin ! videoconvert", 24,false,320,240);
gst[0]->startPipeline();
gst[0]->play();
sleep(1);
gst[1]->setPipeline("v4l2src name=video_source device=/dev/video1 ! image/jpeg,width=320,height=240,framerate=15/1 ! decodebin ! videoconvert", 24,false,320,240);
gst[1]->startPipeline();
gst[1]->play();
}
//--------------------------------------------------------------
void ofApp::update(){
gst[0]->update();
if(gst[0]->isFrameNew()){
test.setFromPixels(gst[0]->getPixels(), 320, 240);
}
gst[1]->update();
if(gst[1]->isFrameNew()){
test2.setFromPixels(gst[1]->getPixels(), 320, 240);
}
if(last){
gst[2]->update();
if(gst[2]->isFrameNew()){
test3.setFromPixels(gst[2]->getPixels(), 320, 240);
}
}
}
//--------------------------------------------------------------
void ofApp::draw(){
test.draw(0,0);
test2.draw(320,0);
if(last)test3.draw(640,0);
}
void ofApp::exit(){
gst[0]->close();
delete gst[0];
gst[1]->close();
delete gst[1];
gst[2]->close();
delete gst[2];
}
//--------------------------------------------------------------
void ofApp::keyReleased(int key){
sleep(0.5);
last=true;
gst[2]->setPipeline("v4l2src name=video_source device=/dev/video2 ! image/jpeg,width=320,height=240,framerate=15/1 ! decodebin ! videoconvert", 24,false,320,240);
sleep(0.1);
gst[2]->startPipeline();
sleep(0.2);
gst[2]->play();
}