bug in parseCaps

I need to get the resolution of the webcam. In the source we have the following:

  // This is a temporary addition until it's decided how to bring back resolution/framerate caps to the official API.
  // The old way of doing things is still listed in the video tutorial:
  // https://processing.org/tutorials/video
  static public String[] getCapabilities(String device) {
    for (int i=0; i < devices.size(); i++) {
      String deviceName = assignDisplayName(devices.get(i), i);
      if (devices.get(i).getDisplayName().equals(device) || devices.get(i).getName().equals(device) || deviceName.equals(device)) {
        return parseCaps(devices.get(i));
      }
    }
    return new String[]{};
  }

The above calls parseCaps which has the following part (this is a piece of it):

      if (0 < indexWidth && 0 < indexHeight && 0 < indexFramerate) {
        stringWidth = cap.substring(indexWidth, cap.indexOf(',', indexWidth));
        stringHeight = cap.substring(indexHeight, cap.indexOf(", format", indexHeight));
        stringFramerate = cap.substring(indexFramerate, cap.indexOf(']', indexFramerate));
      }

An example of the String cap is " video/x-raw, format=(string)YUY2, width=(int)1280, height=(int)720, framerate=(fraction)10/1, pixel-aspect-ratio=(fraction)1/1".

The problem with the above code is that stringHeight = cap.substring(indexHeight, cap.indexOf(", format", indexHeight)); assumes a certain order of the elements being listed. The assumption being made is wrong resulting in the following error:

java.lang.StringIndexOutOfBoundsException: begin 52, end -1, length 127
        at java.base/java.lang.String.checkBoundsBeginEnd(String.java:4606)
        at java.base/java.lang.String.substring(String.java:2709)
        at processing.video.Capture.parseCaps(Capture.java:791)
        at processing.video.Capture.getCapabilities(Capture.java:768)
        at room_activity.Room_Activity.setup(Room_Activity.java:95)
        at processing.core.PApplet.handleDraw(PApplet.java:2051)
        at processing.opengl.PSurfaceJOGL$DrawListener.display(PSurfaceJOGL.java:840)
        at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:692)
        at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:674)
        at jogamp.opengl.GLAutoDrawableBase$2.run(GLAutoDrawableBase.java:443)
        at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1293)
        at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:1147)
        at com.jogamp.newt.opengl.GLWindow.display(GLWindow.java:797)
        at com.jogamp.opengl.util.AWTAnimatorImpl.display(AWTAnimatorImpl.java:81)
        at com.jogamp.opengl.util.AnimatorBase.display(AnimatorBase.java:471)
        at com.jogamp.opengl.util.FPSAnimator$MainTask.run(FPSAnimator.java:245)
        at java.base/java.util.TimerThread.mainLoop(Timer.java:566)
        at java.base/java.util.TimerThread.run(Timer.java:516)

Hello,

This was used to read the camera capability data from Processing Video’s internal device list:

import processing.video.*;

import java.lang.reflect.*;
import java.util.*;

void setup() 
  {
  try 
    {
    String[] cameras = Capture.list();
    printArray(cameras);
    println();
    
    // This failed:
    // println(Capture.getCapabilities(cameras[0]));
    // Related issue:
    // https://github.com/processing/processing-video/issues/224

    Field f = Capture.class.getDeclaredField("devices");
    f.setAccessible(true);
    
    List devices = (List) f.get(null);

    Object dev = devices.get(0);
    Method m = dev.getClass().getMethod("getCaps");

    println("Camera 0: " + cameras[0]);
    println();

    String modes = String.valueOf(m.invoke(dev));
   
    String formattedModes = modes.replace(";", ";\n");
    println(formattedModes);
    }
  catch (Exception e) 
    {
    e.printStackTrace();
    }
  }

/*
Capture.getCapabilities(cameras[0]) failed with:

java.lang.StringIndexOutOfBoundsException: begin 49, end -1, length 133
  at java.base/java.lang.String.checkBoundsBeginEnd(String.java:4606)
  at java.base/java.lang.String.substring(String.java:2709)
  at processing.video.Capture.parseCaps(Unknown Source)
  at processing.video.Capture.getCapabilities(Unknown Source)
  at sketch_260503a.setup(sketch_260503a.java:38)
  at processing.core.PApplet.handleDraw(PApplet.java:2055)
  at processing.awt.PSurfaceAWT$9.callDraw(PSurfaceAWT.java:1388)
  at processing.core.PSurfaceNone$AnimationThread.run(PSurfaceNone.java:356)
*/

It was a long list so test was for one camera only.

My research started here:
https://discourse.processing.org/t/capture-list-showing-duplicate-cameras/47153

Developed through research, testing, and input from various AI tools.

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bug in parseCaps #224

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bug in parseCaps #224

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glvjr commented on May 4, 2026

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