Technical Q&A QA1740

How to capture screen activity to a movie file using AV Foundation on OS X 10.7 Lion and later

Q: How do I capture screen activity to a QuickTime movie on OS X 10.7 Lion and later?

A: On OS X 10.7 Lion and later, the way to make a movie of screen activity is to use AV Foundation.

// Create an image from the entire main display

CGImageRef image = CGDisplayCreateImage(kCGDirectMainDisplay);

See How to take an image snapshot of the screen on Mac OS X Lion for more information.

To perform a real-time screen capture and save it to a QuickTime movie file, you need minimally three AV objects:

An AVCaptureSession object, which coordinates the flow of data from AV input sources to outputs.
An AVCaptureScreenInput object, which is the input data source that provides video data from the given display.
An AVCaptureMovieFileOutput object, which is the output destination for you to write captured media data to a QuickTime movie file.

In the following example, the code creates a capture session, adds a screen input to provide video frames, adds an output destination to save captured frames, starts the flow of data from the input to the output, and stops the flow in 5 seconds. By letting the class conform to the AVCaptureFileOutputRecordingDelegate protocol and setting the recording delegate properly, you can monitor when the recording is finished via the delegate method.

Listing 1 Conforming to the AVCaptureFileOutputRecordingDelegate protocol

#import <Foundation/Foundation.h>

#import <AVFoundation/AVFoundation.h>

@interface Recorder : NSObject <AVCaptureFileOutputRecordingDelegate> {

@private

    AVCaptureSession *mSession;

    AVCaptureMovieFileOutput *mMovieFileOutput;

    NSTimer *mTimer;

-(void)screenRecording:(NSURL *)destPath;

@end

Listing 2 Screen recording example

-(void)screenRecording:(NSURL *)destPath

    // Create a capture session

    mSession = [[AVCaptureSession alloc] init];

    // Set the session preset as you wish

    mSession.sessionPreset = AVCaptureSessionPresetMedium;

    // If you're on a multi-display system and you want to capture a secondary display,

    // you can call CGGetActiveDisplayList() to get the list of all active displays.

    // For this example, we just specify the main display.

    // To capture both a main and secondary display at the same time, use two active

    // capture sessions, one for each display. On Mac OS X, AVCaptureMovieFileOutput

    // only supports writing to a single video track.

    CGDirectDisplayID displayId = kCGDirectMainDisplay;

    // Create a ScreenInput with the display and add it to the session

    AVCaptureScreenInput *input = [[[AVCaptureScreenInput alloc] initWithDisplayID:displayId] autorelease];

    if (!input) {

        [mSession release];

        mSession = nil;

        return;

    if ([mSession canAddInput:input])

        [mSession addInput:input];

    // Create a MovieFileOutput and add it to the session

    mMovieFileOutput = [[[AVCaptureMovieFileOutput alloc] init] autorelease];

    if ([mSession canAddOutput:mMovieFileOutput])

        [mSession addOutput:mMovieFileOutput];

    // Start running the session

    [mSession startRunning];

    // Delete any existing movie file first

    if ([[NSFileManager defaultManager] fileExistsAtPath:[destPath path]])

        NSError *err;

        if (![[NSFileManager defaultManager] removeItemAtPath:[destPath path] error:&err])

            NSLog(@"Error deleting existing movie %@",[err localizedDescription]);

    // Start recording to the destination movie file

    // The destination path is assumed to end with ".mov", for example, @"/users/master/desktop/capture.mov"

    // Set the recording delegate to self

    [mMovieFileOutput startRecordingToOutputFileURL:destPath recordingDelegate:self];

    // Fire a timer in 5 seconds

    mTimer = [[NSTimer scheduledTimerWithTimeInterval:5 target:self selector:@selector(finishRecord:) userInfo:nil repeats:NO] retain];

-(void)finishRecord:(NSTimer *)timer

    // Stop recording to the destination movie file

    [mMovieFileOutput stopRecording];

    [mTimer release];

    mTimer = nil;

// AVCaptureFileOutputRecordingDelegate methods

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error

    NSLog(@"Did finish recording to %@ due to error %@", [outputFileURL description], [error description]);

    // Stop running the session

    [mSession stopRunning];

    // Release the session

    [mSession release];

    mSession = nil;

Document Revision History

Date	Notes
2015-05-20	Added additional notes about capturing the main and secondary displays at the same time. Other miscellaneous changes.
2011-08-10	Corrected a link.
2011-05-13	New document that shows how to capture screen activity to a movie file using AV Foundation on OS X 10.7 Lion and later.