# Send video frame into OpenCV?
**URL:** https://discourse.processing.org/t/send-video-frame-into-opencv/18075
**Category:** Libraries
**Created:** [February 24, 2020, 5:34pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075 "2020-02-24T17:34:20Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@jeffthompson](https://discourse.processing.org/u/jeffthompson)
#### Post date: [February 24, 2020, 5:34pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/1 "2020-02-24T17:34:20Z")
I’m trying to read the frame of a video and send it into OpenCV for blob detection, but am getting a strange error.
With this simple example:
```auto
import processing.video.*;
Movie mov;
OpenCV cv;
void setup() {
size(640, 360);
mov = new Movie(this, sketchPath("transit.mov"));
mov.play();
mov.jump(0);
cv = new OpenCV(this, mov.width, mov.height);
}
void draw() {
if (mov.available()) {
mov.read();
cv.loadImage(mov);
cv.threshold(150);
image(cv.getOutput(), 0, 0);
}
}
```
I get the error (three times, then it quits):
```auto
IndexOutOfBoundsException: Index: 3, Size: 0
IndexOutOfBoundsException: Index: 3, Size: 0
```
The video is from the Video library example, so I know it plays ok in Processing. Help!
---
### Author:  [@20203](https://discourse.processing.org/u/20203)
#### Post date: [February 25, 2020, 11:57pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/2 "2020-02-25T23:57:16Z")
Which line is the error coming from? Do you have a .mov file called “transit.mov”?
---
### Author:  [@jeffthompson](https://discourse.processing.org/u/jeffthompson)
#### Post date: [February 26, 2020, 1:22am UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/3 "2020-02-26T01:22:58Z")
Sorry – it’s on the `cv.loadImage(mov);` line. Definitely have the video and it loads/plays fine. Crashes only when I try to pass the frame into OpenCV.
---
### Author:  [@jeffthompson](https://discourse.processing.org/u/jeffthompson)
#### Post date: [February 26, 2020, 8:16pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/4 "2020-02-26T20:16:27Z")
Ok, I got this to work but it’s a total hack:
```auto
import gab.opencv.*;
import processing.video.*;
Movie mov;
OpenCV cv;
void setup() {
size(640, 360);
mov = new Movie(this, sketchPath("transit.mov"));
mov.play();
mov.jump(0);
mov.loop();
cv = new OpenCV(this, mov.width, mov.height);
}
void draw() {
if (mov.available()) {
mov.read();
// display the frame onscreen
image(mov, 0,0);
// then pass it to OpenCV using get()
cv = new OpenCV(this, get(0,0,width,height));
cv.threshold(150);
image(cv.getOutput(), 0, 0);
}
}
```
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [February 27, 2020, 1:05am UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/5 "2020-02-27T01:05:45Z")
> [@jeffthompson](#):
>
> … but it’s a total hack:
- For a better performance you can use a separate cloned PImage.
- Then use **arrayCopy()** to transfer the library’s PImage to the cloned 1:
- [arrayCopy() / Reference / Processing.org](http://Processing.org/reference/arrayCopy_.html)
- I believe it’s safe now to pass the cloned PImage to the OpenCV instance.
- Take a look at this example sketch below using Capture w/ **arrayCopy()** and a separate PImage:
```auto
// https://Discourse.Processing.org/t/send-video-frame-into-opencv/18075/5
// GoToLoop 2020-Feb-26
import processing.video.Capture;
Capture cam;
PImage frame = new PImage();
static final int CAM = 1, DELAY = 5;
void setup() {
size(640, 480);
initFeed();
println("Cam's size:", cam.width, 'x', cam.height);
}
void draw() {
set(0, 0, frame);
getSurface().setTitle( str(round(frameRate)) );
}
void captureEvent(final Capture c) {
c.read();
if (frame.width == c.width) {
c.loadPixels();
arrayCopy(c.pixels, frame.pixels);
frame.updatePixels();
} else frame = c.get();
}
void initFeed() {
final String[] cams = Capture.list();
printArray(cams);
println("\nChosen Cam #" + CAM + ':', cams[CAM], ENTER);
( cam = new Capture(this, cams[CAM]) ).start();
println("cam.width: " + cam.width);
while (cam.width == 0) delay(DELAY);
println("cam.width: " + cam.width + ENTER);
if (cam.width > 0) getSurface().setSize(cam.width, cam.height);
}
```
---
### Author:  [@jeffthompson](https://discourse.processing.org/u/jeffthompson)
#### Post date: [February 27, 2020, 1:28pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/6 "2020-02-27T13:28:59Z")
Thanks! I’m actually not seeing any improvement in performance here, which is surprising. This sample video (from the `Video` library) is `640 x 360` but I’m still getting 60fps on both.
Would still be interested to know if this is an OpenCV or Video lib issue.
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [February 27, 2020, 1:33pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/7 "2020-02-27T13:33:43Z")
> [@jeffthompson](#):
>
> Would still be interested to know if this is an OpenCV or Video lib issue.
- You need to consider that the video library is constantly mutating its _pixels[]_ internal array.
- Therefore passing its reference to another library can be problematic depending on what the other library does to it.
- Passing instead a vanilla PImage clone to OpenCV seems like an excellent workaround IMO.
---
### Author:  [@jeffthompson](https://discourse.processing.org/u/jeffthompson)
#### Post date: [February 27, 2020, 1:44pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/8 "2020-02-27T13:44:45Z")
Totally – just weird because you can easily pass a `Capture` object from the same lib with no issues.
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [February 27, 2020, 1:49pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/9 "2020-02-27T13:49:28Z")
> [@jeffthompson](#):
>
> … you can easily pass a Capture object from the same lib with no issues.
Is it true? In my posted example I’m passing the cloned PImage _frame_ as **image()**'s argument in place of the original Capture _cam_.
The idea here is that you can use the same strategy when invoking OpenCV::**loadImage()**.
---
### Author:  [@neilcsmith](https://discourse.processing.org/u/neilcsmith)
#### Post date: [February 27, 2020, 4:02pm UTC](https://discourse.processing.org/t/send-video-frame-into-opencv/18075/10 "2020-02-27T16:02:52Z")
> [@GoToLoop](#):
>
> You need to consider that the video library is constantly mutating its _pixels[]_ internal array.
No it isn’t.
> [@GoToLoop](#):
>
> println(“Cam’s size:”, cam.width, ‘x’, cam.height);
This on the other hand is more interesting. The width and height of the Movie are probably going to be 0 when the `cv = new OpenCV(this, mov.width, mov.height);` line executes. Try outputting them. If so, maybe try -
```auto
if (mov.available()) {
mov.read();
if (cv == null) {
cv = new OpenCV(this, mov.width, mov.height);
}
```