为什么使用 AVCaptureSession、AVAssetWriter 和 AVPlayer 录制和重放视频会卡顿？

Question

我正在尝试制作一个显示相机预览的应用程序，然后在某些情况下开始使用语音输入录制此预览，最后重复录制的电影。

我已经编写了用于预览/录制/重放的类以及管理它们协调的控制器。

看起来这些函数在独立调用时工作得很好，但是我无法让它们一起工作：重播视频时，声音运行，但图像需要大约五秒钟的时间才能显示，然后断断续续。

这是我的代码：

预览：

- (void) createSession
{
    _session = [[AVCaptureSession alloc] init];

    AVCaptureDevice *device = [AVCaptureDevice deviceWithUniqueID:FRONT_CAMERA_ID];
    if (!device) device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

    NSError *error = nil;
    _cVideoInput = [[AVCaptureDeviceInput deviceInputWithDevice:device error:&error] retain];
    if (!error) [_session addInput:_cVideoInput];

    device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];

    error = nil;
    _cAudioInput = [[AVCaptureDeviceInput deviceInputWithDevice:device error:&error] retain];
    if (!error) [_session addInput:_cAudioInput];

    _cameraLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_session];
    _cameraLayer.frame = self.bounds;
    [self.layer addSublayer:_cameraLayer];

    _videoOutput = [[AVCaptureVideoDataOutput alloc] init];
    [_session setSessionPreset:AVCaptureSessionPreset640x480];
    [_videoOutput setVideoSettings:[NSDictionary dictionaryWithContentsOfFile:VIDEO_SETTINGS]];

    _audioOutput = [[AVCaptureAudioDataOutput alloc] init];

    dispatch_queue_t queue = dispatch_queue_create(OUTPUT_QUEUE_NAME, NULL);
    [_videoOutput setSampleBufferDelegate:self queue:queue];
    [_session addOutput:_videoOutput];

    [_audioOutput setSampleBufferDelegate:self queue:queue];
    [_session addOutput:_audioOutput];

    dispatch_set_context(queue, self);
    dispatch_set_finalizer_f(queue, queue_finalizer);

    dispatch_release(queue);

    [_session startRunning];
}

- (void) deleteSession
{
    [_session stopRunning];

    [(AVCaptureVideoPreviewLayer *)_cameraLayer setSession:nil];
    [_cameraLayer removeFromSuperlayer];
    [_cameraLayer release];
    _cameraLayer = nil;

    [_audioOutput setSampleBufferDelegate:nil queue:NULL];
    [_videoOutput setSampleBufferDelegate:nil queue:NULL];

    [_audioOutput release];
    _audioOutput = nil;

    [_videoOutput release];
    _videoOutput = nil;

    [_cAudioInput release];
    _cAudioInput = nil;

    [_cVideoInput release];
    _cVideoInput = nil;

    NSArray *inputs = [_session inputs];
    for (AVCaptureInput *input in inputs)
         [_session removeInput:input];

    NSArray *outputs = [_session outputs];
    for (AVCaptureOutput *output in outputs)
        [_session removeOutput:output];

    [_session release];
    _session = nil;
}

录音：

- (void) createWriter
{
    NSString *file = [self file];

    if ([[NSFileManager defaultManager] fileExistsAtPath:file]) [[NSFileManager defaultManager] removeItemAtPath:file error:NULL];

    NSError *error = nil;
    _writer = [[AVAssetWriter assetWriterWithURL:[NSURL fileURLWithPath:file] fileType:AVFileTypeQuickTimeMovie error:&error] retain];

    if (error)
    {
        [_writer release];
        _writer = nil;

        NSLog(@"%@", error);
        return;
    }

    AudioChannelLayout acl;
    bzero( &acl, sizeof(acl));
    acl.mChannelLayoutTag = kAudioChannelLayoutTag_Mono;

    NSDictionary *settings = [NSDictionary dictionaryWithObjectsAndKeys:
                              [NSNumber numberWithInt:kAudioFormatMPEG4AAC], AVFormatIDKey,
                              [NSNumber numberWithFloat:44100.0], AVSampleRateKey,
                              [NSNumber numberWithInt:1], AVNumberOfChannelsKey,
                              [NSNumber numberWithInt:64000], AVEncoderBitRateKey,
                              [NSData dataWithBytes:&acl length:sizeof(acl)], AVChannelLayoutKey,
                              nil ];

    _wAudioInput = [[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:settings] retain];

    [_writer addInput:_wAudioInput];

    settings = [NSDictionary dictionaryWithObjectsAndKeys:
                AVVideoCodecH264, AVVideoCodecKey,
                [NSNumber numberWithInt:640], AVVideoWidthKey,
                [NSNumber numberWithInt:480], AVVideoHeightKey,
                nil];

    _wVideoInput = [[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:settings] retain];

    [_writer addInput:_wVideoInput];
}

- (void) deleteWriter
{
    [_wVideoInput release];
    _wVideoInput = nil;

    [_wAudioInput release];
    _wAudioInput = nil;

    [_writer release];
    _writer = nil;
}

- (void) RecordingAudioWithBuffer:(CMSampleBufferRef)sampleBuffer
{
    if (![self canRecordBuffer:sampleBuffer])
        return;

    if ([_wAudioInput isReadyForMoreMediaData])
        [_wAudioInput appendSampleBuffer:sampleBuffer];
}

- (void) RecordingVideoWithBuffer:(CMSampleBufferRef)sampleBuffer
{
    if (![self canRecordBuffer:sampleBuffer])
        return;

    if ([_wVideoInput isReadyForMoreMediaData])
        [_wVideoInput appendSampleBuffer:sampleBuffer];
}

播放：

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    AVPlayerItem *item = (AVPlayerItem *)object;
    [item removeObserver:self forKeyPath:@"status"];

    switch (item.status) 
    {
        case AVPlayerItemStatusReadyToPlay:

            [_player seekToTime:kCMTimeZero];
            [_player play];

            [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(finishPlaying:) name:AVPlayerItemDidPlayToEndTimeNotification object:item];
            break;
        case AVPlayerItemStatusUnknown:
        case AVPlayerItemStatusFailed:
            break;
        default:
            break;
    }
}

- (void) finishPlaying:(NSNotification *)notification
{
    [_player pause];
    [_playerLayer removeFromSuperlayer];

    [_playerLayer release];
    _playerLayer = nil;

    [_player release];
    _player = nil;

    [[NSNotificationCenter defaultCenter] removeObserver:self name:AVPlayerItemDidPlayToEndTimeNotification object:nil];
}

- (void) play:(NSString *)path
{
    _player = [[AVPlayer playerWithURL:[NSURL fileURLWithPath:path]] retain];

    _playerLayer = [[AVPlayerLayer playerLayerWithPlayer:_player] retain];
    _playerLayer.transform = CATransform3DScale(CATransform3DMakeRotation(M_PI_2, 0, 0, 1), 1, -1, 1);
    _playerLayer.frame = self.bounds;
    [self.layer addSublayer:_playerLayer];

    [_player.currentItem addObserver:self forKeyPath:@"status" options:0 context:NULL];
}

Answer 1

我遇到了类似的问题，虽然这并没有完全解决它，但确实有很大帮助：
如果您不准备再次写入，不要只是丢失示例缓冲区，而是尝试让设备休眠一会儿，然后重新评估是否可以写入数据。

- (void) RecordingVideoWithBuffer:(CMSampleBufferRef)sampleBuffer
{
if (![self canRecordBuffer:sampleBuffer])
    return;

if (!_wVideoInput.readyForMoreMediaData && _isRecording)
{
    [self performSelector:@selector(RecordingVideoWithBuffer:) withObject:(__bridge id)(sampleBuffer) afterDelay:0.05];
    return;
}

[_wVideoInput appendSampleBuffer:sampleBuffer];

如果您不使用 ARC，则只需使用sampleBuffer即可。但ARC需要添加__bridge。

编辑：
我使用了 PerformSelector 和 return，而不是使用 NSThread sleep 的 while 循环，因为它是非阻塞的。
封锁很糟糕。