How to access external usb camera on unrooted android devices -

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i want access extern usb cameras via v4l on android.

i tried simplewebcam. after slight modifications of original source codes, achieved make work on rooted android device. however, on unrooted devices, keeps complaining "not have permission access "/dev/video*". checked permission of /dev/video* "ls -l /dev/video*", , got

crw-rw---- system camera 81, 0 2015-08-18 18:31 video0

i understand means /dev/video* owned system, , readable/writable users in group "camera". think if add

<uses-permission android:name="android.permission.camera" />

in manifest of app, user id of app added group "camera", app allowed read data /dev/video*.

but, still complains "not have permission access /dev/video*" now.

i tried

<uses-permission android:name="android.permission.camera" /> <uses-feature android:name="android.hardware.camera" /> <uses-feature android:name="android.hardware.camera.autofocus" />

, still not working.

do miss somthing or misunderstand somthing. or discussion appreciated.

the codes used open device 

int opendevice(int i) { struct stat st;  sprintf(dev_name,"/dev/video%d",i);  if (-1 == stat (dev_name, &st)) {     loge("cannot identify '%s': %d, %s", dev_name, errno, strerror (errno));     return error_local; }  if (!s_ischr (st.st_mode)) {     loge("%s no device", dev_name);     return error_local; }  fd = open (dev_name, o_rdwr);// | o_nonblock, 0);  if (-1 == fd) {     loge("cannot open '%s': %d, %s", dev_name, errno, strerror (errno));     return error_local; } return success_local; }

the return value of open -1, logcat: 

 cannot open '/dev/video3': 13, permission denied

i achieve read images external usb camera on unrooted android devices using opensource project named uvccamera. here link, https://github.com/saki4510t/uvccamera


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