Loading video files using VideoCapture in Android

asked 2017-02-10 06:13:36 -0600

iuq
6 ●1 ●8 ●3

Hi,

My aim is to load two video files, grabbing the frames from each file and creating a single frame.

I have understood I can use VideoCapture java class to load files and use Mat class to work on individual frames.

I have two AVI files stored at /storage/emulated/0/Download/received_files/<file>.avi. However VideoCapture is unable to open the files.

VideoCapture vc1 = new VideoCapture();
 VideoCapture vc2 = new VideoCapture();

 if (!vc1.open(video1)) {
    Log.e(TAG, "Could not open the video file1");
 } else {
    Log.i(TAG, "Video1 loaded");
 }

 if (!vc2.open(video1)) {
    Log.e(TAG, "Could not open the video file1");
 } else {
    Log.i(TAG, "Video2 loaded");
 }

It always pronts "Could not open ..." message. I have tested the file paths using File.exists and it returns true. What am I missing here?

I am using OpenCV 3.2.0 for Android and Android lollipop.

My Android setup is done properly and I can view the camera in JavaCameraView.

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2 answers

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answered 2017-02-10 06:35:52 -0600

berak
32993 ●7 ●81 ●312

unfortunately, you cannot load arbitrary video files on android, only MJPG codec in an avi container is supported from opencv (due to missing backend, like ffmpeg or gstreamer)

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Thanks Berak for these pointer, I'll explore it more.

In fact, end product is stitching/merging multiple streams from cameras connected to an Android tablet via OTG USB hub. I am novice in this area and that is why I have picked up working with couple of offline videos first. I hope my approach is correct?

Great if you could share some links regrading opencv+ffmpeg on Android or anything related to my project! Thanks.

iuq ( 2017-02-11 00:42:01 -0600 )edit

in that case, you might be better off, avoiding opencv, and using ffmpeg directly

berak ( 2017-02-11 00:52:20 -0600 )edit

seems ffmpeg can be used as a plugin to opencv!

iuq ( 2017-02-11 06:20:50 -0600 )edit

@berak, I tried couple of videos both in AVI and MP4 format with respective extensions to no avail. I don't know how to put MPEG in AVI! I have tried this command ffmpeg -i input.avi -c:v mpeg4 -vtag xvid output.avi to convert the video but video was still not loaded by VideoCapture.

iuq ( 2017-02-13 02:07:17 -0600 )edit

again, xvid codec is not supported natively. you need MJPG, as said before.

berak ( 2017-02-13 02:09:35 -0600 )edit

Got it finally! My source video is input.mp4. First, I converted that to MJPEG ffmpeg -i input.mp4 -vcodec mjpeg output.mjpeg and then ffmpeg -i output.mjpeg -vocdec output.avi. My bad, initially I read MJPG as MPEG in you reply! Thanks.

iuq ( 2017-02-13 03:58:12 -0600 )edit

Hi, Could you please explain how do you run "ffmpeg -i input.mp4 -vcodec mjpeg output.mjpeg" in an Android app? Do you install ffmpeg on the device and run something like "Process process = Runtime.getRuntime().exec(commandLine);" in your code?