Android VideoCapture from video file always return null

edit

I use example code as following to try open MP4 video file and put some text to video file but open result always return failed.

extern "C"
{
//.... something code............

const char* arrURL = "mnt/sdcard/Download/VID_20140317_104750.mp4";
string source(arrURL);

VideoCapture inputVideo;              // Open input
//inputVideo.open(source);

if (!inputVideo.open(source)) -> alway return false here...
{
    env->ReleaseStringUTFChars(URL, arrURL);
    env->ReleaseStringUTFChars(sInputText, arrInputText);
    return;
}
//....

i used eclipse CDT - juno, NDK-r9, OpenCV 2.4.8 do everyone can help me answer some questions? - VideoCapture can not be supported on android? - Do you know any other solution on android? (not FFMPEG lib)

Thanks