Question

我正在玩AVFoundation，灵感来自this Technical Q&A code sample - 通过Lion上的AVFoundation进行屏幕截图。

示例代码运行良好，但如果我将 AVCaptureSessionPresetMedium 更改为 AVCaptureSessionPresetHigh 且跟随错误，则一直都会失败：

由于错误错误，即将完成录制 Domain = AVFoundationErrorDomain Code = -11812“录制已停止” UserInfo = 0x1001ccb60 {AVErrorRecordingSuccessfullyFinishedKey = false， NSLocalizedRecoverySuggestion =停止使用的任何其他操作录制设备，然后再试一次。，NSLocalizedDescription =录制停止}

会话停止时会发生这种情况。错误代码为AVErrorMediaDiscontinuity。使用[mSession stopRunning]正常停止录制。

我仔细阅读了所有文档，但无法找到解释为什么会在切换会话预设时发生这种情况的说明。对我来说，它似乎是一个错误。 [mSession canSetSessionPreset：AVCaptureSessionPresetHigh]甚至返回true。简单的源代码：

@implementation ScreenRecorder

-(void)screenRecording:(NSURL *)destPath
{
    // Create a capture session
    mSession = [[AVCaptureSession alloc] init];

    if ([mSession canSetSessionPreset:AVCaptureSessionPresetHigh])
        NSLog(@"Can set high preset");
    else
        NSLog(@"CANNOT set high preset");

    [mSession setSessionPreset: AVCaptureSessionPresetHigh];// Fails, but AVCaptureSessionPresetMedium works splendidly


    input = [[AVCaptureScreenInput alloc] initWithDisplayID: kCGDirectMainDisplay];
    if (!input) {
        mSession = nil;
        NSLog(@"Input not valid!");
        return;
    }
    if ([mSession canAddInput:input]){
        [mSession addInput:input];
    }
    else
        NSLog(@"Could not add input!!");


    mMovieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
    if ([mSession canAddOutput:mMovieFileOutput])
        [mSession addOutput:mMovieFileOutput];
    else
        NSLog(@"Could not add movie file output!!");

    [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]);
        }
    }

    NSLog(@"Starting recording..");
    [mMovieFileOutput startRecordingToOutputFileURL:destPath recordingDelegate:self];
}

-(void)stopRecording
{
    NSLog(@"Stopping recording..");
    [mMovieFileOutput stopRecording];
}

//
// AVCaptureFileOutputRecordingDelegate methods
//
- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didStartRecordingToOutputFileAtURL:(NSURL *)fileURL fromConnections:(NSArray *)connections
{
    NSLog(@"Started recording to %@", [fileURL description]);
}

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput willFinishRecordingToOutputFileAtURL:(NSURL *)fileURL fromConnections:(NSArray *)connections error:(NSError *)error
{
    NSLog(@"About to finish recording due to error %@", [error description]);
}

- (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]);

    [mSession stopRunning];
    mSession = nil;
}

@end

记录输出：

2013-05-28 19:51:45.058 ScreenEmailer[1330:303] Can set high preset 
2013-05-28 19:51:45.584 ScreenEmailer[1330:303] Starting recording.. 
2013-05-28 19:53:39.757 ScreenEmailer[1330:303] Stopping recording.. 
2013-05-28 19:53:44.758 ScreenEmailer[1330:303] About to finish recording due to error Error Domain=AVFoundationErrorDomain Code=-11812 "Recording Stopped" UserInfo=0x1001ccb60 {AVErrorRecordingSuccessfullyFinishedKey=false, NSLocalizedRecoverySuggestion=Stop any other actions using the recording device and try again., NSLocalizedDescription=Recording Stopped}

为什么会这样？如何配置更高的录音质量？

由于

Answer 1

结果AVCaptureSessionPresetHigh要求您定义录制区域：

mSession = [[AVCaptureSession alloc] init];
[mSession setSessionPreset: AVCaptureSessionPresetHigh];
input = [[AVCaptureScreenInput alloc] initWithDisplayID: kCGDirectMainDisplay];
input.cropRect = CGRectMake(0.0, 0.0, 700.0, 700.0); // is required for AVCaptureSessionPresetHigh

此后录音工作非常精彩。

感谢Gordon Apple＆lt; 3

AVFoundation：AVCaptureSessionPresetHigh可防止录制完成

1 个答案: