我正在使用AVFoundation。我想用两个（正面和背面）相机录制视频。当我将相机模式改回前方时，我在一侧录制视频，相机仍然会冻结。是否可以连续录制视频。
示例代码：
- (void) startup
{
if (_session == nil)
{
NSLog(@"Starting up server");
self.isCapturing = NO;
self.isPaused = NO;
_currentFile = 0;
_discont = NO;
// create capture device with video input
_session = [[AVCaptureSession alloc] init];
AVCaptureDevice *backCamera = [self frontCamera];
AVCaptureDeviceInput* input = [AVCaptureDeviceInput deviceInputWithDevice:backCamera error:nil];
[_session addInput:input];
// audio input from default mic
AVCaptureDevice* mic = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
AVCaptureDeviceInput* micinput = [AVCaptureDeviceInput deviceInputWithDevice:mic error:nil];
[_session addInput:micinput];
// create an output for YUV output with self as delegate
_captureQueue = dispatch_queue_create("com.softcraftsystems.comss", DISPATCH_QUEUE_SERIAL);
AVCaptureVideoDataOutput* videoout = [[AVCaptureVideoDataOutput alloc] init];
[videoout setSampleBufferDelegate:self queue:_captureQueue];
NSDictionary* setcapSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange], kCVPixelBufferPixelFormatTypeKey,
nil];
videoout.videoSettings = setcapSettings;
[_session addOutput:videoout];
_videoConnection = [videoout connectionWithMediaType:AVMediaTypeVideo];
// find the actual dimensions used so we can set up the encoder to the same.
NSDictionary* actual = videoout.videoSettings;
_cy = [[actual objectForKey:@"Height"] integerValue];
_cx = [[actual objectForKey:@"Width"] integerValue];
AVCaptureAudioDataOutput* audioout = [[AVCaptureAudioDataOutput alloc] init];
[audioout setSampleBufferDelegate:self queue:_captureQueue];
[_session addOutput:audioout];
_audioConnection = [audioout connectionWithMediaType:AVMediaTypeAudio];
// for audio, we want the channels and sample rate, but we can't get those from audioout.audiosettings on ios, so
// we need to wait for the first sample
// start capture and a preview layer
[_session startRunning];
_preview = [AVCaptureVideoPreviewLayer layerWithSession:_session];
_preview.videoGravity = AVLayerVideoGravityResizeAspectFill;
}
}
- (AVCaptureDevice *)frontCamera
{
NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
for (AVCaptureDevice *device in devices) {
if ([device position] == AVCaptureDevicePositionFront) {
return device;
}
}
return nil;
}
- (AVCaptureDevice *)backCamera
{
NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
for (AVCaptureDevice *device in devices) {
if ([device position] == AVCaptureDevicePositionBack) {
return device;
}
}
return nil;
}
- (void) startupFront
{
_session = nil;
[_session stopRunning];
if (_session == nil)
{
NSLog(@"Starting up server");
self.isCapturing = NO;
self.isPaused = NO;
_currentFile = 0;
_discont = NO;
// create capture device with video input
_session = [[AVCaptureSession alloc] init];
AVCaptureDevice *backCamera = [self backCamera];
AVCaptureDeviceInput* input = [AVCaptureDeviceInput deviceInputWithDevice:backCamera error:nil];
[_session addInput:input];
// audio input from default mic
AVCaptureDevice* mic = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
AVCaptureDeviceInput* micinput = [AVCaptureDeviceInput deviceInputWithDevice:mic error:nil];
[_session addInput:micinput];
// create an output for YUV output with self as delegate
_captureQueue = dispatch_queue_create("com.softcraftsystems.comss", DISPATCH_QUEUE_SERIAL);
AVCaptureVideoDataOutput* videoout = [[AVCaptureVideoDataOutput alloc] init];
[videoout setSampleBufferDelegate:self queue:_captureQueue];
NSDictionary* setcapSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange], kCVPixelBufferPixelFormatTypeKey,
nil];
videoout.videoSettings = setcapSettings;
[_session addOutput:videoout];
_videoConnection = [videoout connectionWithMediaType:AVMediaTypeVideo];
// find the actual dimensions used so we can set up the encoder to the same.
NSDictionary* actual = videoout.videoSettings;
_cy = [[actual objectForKey:@"Height"] integerValue];
_cx = [[actual objectForKey:@"Width"] integerValue];
AVCaptureAudioDataOutput* audioout = [[AVCaptureAudioDataOutput alloc] init];
[audioout setSampleBufferDelegate:self queue:_captureQueue];
[_session addOutput:audioout];
_audioConnection = [audioout connectionWithMediaType:AVMediaTypeAudio];
// for audio, we want the channels and sample rate, but we can't get those from audioout.audiosettings on ios, so
// we need to wait for the first sample
// start capture and a preview layer
[_session startRunning];
_preview = [AVCaptureVideoPreviewLayer layerWithSession:_session];
_preview.videoGravity = AVLayerVideoGravityResizeAspectFill;
}
}
- (void) startCapture
{
@synchronized(self)
{
if (!self.isCapturing)
{
NSLog(@"starting capture");
// create the encoder once we have the audio params
_encoder = nil;
self.isPaused = NO;
_discont = NO;
_timeOffset = CMTimeMake(0, 0);
self.isCapturing = YES;
}
}
}
- (void) stopCapture
{
@synchronized(self)
{
if (self.isCapturing)
{
NSString* filename = [NSString stringWithFormat:@"capture%d.mp4", _currentFile];
NSString* path = [NSTemporaryDirectory() stringByAppendingPathComponent:filename];
NSURL* url = [NSURL fileURLWithPath:path];
_currentFile++;
// serialize with audio and video capture
self.isCapturing = NO;
dispatch_async(_captureQueue, ^{
[_encoder finishWithCompletionHandler:^{
self.isCapturing = NO;
_encoder = nil;
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library writeVideoAtPathToSavedPhotosAlbum:url completionBlock:^(NSURL *assetURL, NSError *error){
NSLog(@"save completed");
[[NSFileManager defaultManager] removeItemAtPath:path error:nil];
}];
}];
});
}
}
}
- (void) pauseCapture
{
@synchronized(self)
{
if (self.isCapturing)
{
NSLog(@"Pausing capture");
self.isPaused = YES;
_discont = YES;
}
}
}
- (void) resumeCapture
{
@synchronized(self)
{
if (self.isPaused)
{
NSLog(@"Resuming capture");
self.isPaused = NO;
}
}
}
- (CMSampleBufferRef) adjustTime:(CMSampleBufferRef) sample by:(CMTime) offset
{
CMItemCount count;
CMSampleBufferGetSampleTimingInfoArray(sample, 0, nil, &count);
CMSampleTimingInfo* pInfo = malloc(sizeof(CMSampleTimingInfo) * count);
CMSampleBufferGetSampleTimingInfoArray(sample, count, pInfo, &count);
for (CMItemCount i = 0; i < count; i++)
{
pInfo[i].decodeTimeStamp = CMTimeSubtract(pInfo[i].decodeTimeStamp, offset);
pInfo[i].presentationTimeStamp = CMTimeSubtract(pInfo[i].presentationTimeStamp, offset);
}
CMSampleBufferRef sout;
CMSampleBufferCreateCopyWithNewTiming(nil, sample, count, pInfo, &sout);
free(pInfo);
return sout;
}
- (void) setAudioFormat:(CMFormatDescriptionRef) fmt
{
const AudioStreamBasicDescription *asbd = CMAudioFormatDescriptionGetStreamBasicDescription(fmt);
_samplerate = asbd->mSampleRate;
_channels = asbd->mChannelsPerFrame;
}
- (void) captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
BOOL bVideo = YES;
@synchronized(self)
{
if (!self.isCapturing || self.isPaused)
{
return;
}
if (connection != _videoConnection)
{
bVideo = NO;
}
if ((_encoder == nil) && !bVideo)
{
CMFormatDescriptionRef fmt = CMSampleBufferGetFormatDescription(sampleBuffer);
[self setAudioFormat:fmt];
NSString* filename = [NSString stringWithFormat:@"capture%d.mp4", _currentFile];
NSString* path = [NSTemporaryDirectory() stringByAppendingPathComponent:filename];
_encoder = [VideoEncoder encoderForPath:path Height:_cy width:_cx channels:_channels samples:_samplerate];
}
if (_discont)
{
if (bVideo)
{
return;
}
_discont = NO;
// calc adjustment
CMTime pts = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
CMTime last = bVideo ? _lastVideo : _lastAudio;
if (last.flags & kCMTimeFlags_Valid)
{
if (_timeOffset.flags & kCMTimeFlags_Valid)
{
pts = CMTimeSubtract(pts, _timeOffset);
}
CMTime offset = CMTimeSubtract(pts, last);
NSLog(@"Setting offset from %s", bVideo?"video": "audio");
NSLog(@"Adding %f to %f (pts %f)", ((double)offset.value)/offset.timescale, ((double)_timeOffset.value)/_timeOffset.timescale, ((double)pts.value/pts.timescale));
// this stops us having to set a scale for _timeOffset before we see the first video time
if (_timeOffset.value == 0)
{
_timeOffset = offset;
}
else
{
_timeOffset = CMTimeAdd(_timeOffset, offset);
}
}
_lastVideo.flags = 0;
_lastAudio.flags = 0;
}
// retain so that we can release either this or modified one
CFRetain(sampleBuffer);
if (_timeOffset.value > 0)
{
CFRelease(sampleBuffer);
sampleBuffer = [self adjustTime:sampleBuffer by:_timeOffset];
}
// record most recent time so we know the length of the pause
CMTime pts = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
CMTime dur = CMSampleBufferGetDuration(sampleBuffer);
if (dur.value > 0)
{
pts = CMTimeAdd(pts, dur);
}
if (bVideo)
{
_lastVideo = pts;
}
else
{
_lastAudio = pts;
}
}
// pass frame to encoder
[_encoder encodeFrame:sampleBuffer isVideo:bVideo];
CFRelease(sampleBuffer);
}
- (void) shutdown
{
NSLog(@"shutting down server");
if (_session)
{
[_session stopRunning];
_session = nil;
}
[_encoder finishWithCompletionHandler:^{
NSLog(@"Capture completed");
}];
}
答案 0 :(得分：0)
据我说。这是不可能的，当我们切换相机时继续录制， 因为，它们之间存在分辨率和质量差异，视频在整个视频中只能有一种分辨率和质量。 第二，每次在相机之间切换时，它都会分配并初始化相机。 不幸的是，根据我不可能。 但是如果你找到解决方案，请告诉我。