第一次在这里问一个问题。我希望帖子清晰，示例代码格式正确。
我正在尝试AVFoundation和时间推移摄影。
我的目的是从iOS设备（我的iPod touch，版本4）的摄像机中抓取每个第N帧，并将每个帧写入文件以创建游戏中时光倒流。我正在使用AVCaptureVideoDataOutput，AVAssetWriter和AVAssetWriterInput。
问题是，如果我使用传递给
captureOutput:idOutputSampleBuffer:fromConnection:的CMSampleBufferRef，每帧的回放是原始输入帧之间的时间长度。帧率为1fps。我希望得到30fps。
我尝试使用
CMSampleBufferCreateCopyWithNewTiming()，但是在将13帧写入文件后，
captureOutput:idOutputSampleBuffer:fromConnection:停止被调用。界面处于活动状态，我可以点击按钮停止捕获并将其保存到照片库进行播放。它看起来像我想要的那样回放，30fps，但它只有那13帧。
如何实现30fps播放的目标？ 如何判断应用程序丢失的原因以及原因？
我已经放置了一个名为useNativeTime的标志，因此我可以测试这两种情况。当设置为YES时，我得到了我感兴趣的所有帧，因为回调不会“迷路”。当我将该标志设置为NO时，我只处理了13帧，并且再也没有返回到该方法。如上所述，在这两种情况下我都可以播放视频。
感谢您的帮助。
这是我正在尝试重新定时的地方。
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
BOOL useNativeTime = NO;
BOOL appendSuccessFlag = NO;
//NSLog(@"in captureOutpput sample buffer method");
if( !CMSampleBufferDataIsReady(sampleBuffer) )
{
NSLog( @"sample buffer is not ready. Skipping sample" );
//CMSampleBufferInvalidate(sampleBuffer);
return;
}
if (! [inputWriterBuffer isReadyForMoreMediaData])
{
NSLog(@"Not ready for data.");
}
else {
// Write every first frame of n frames (30 native from camera).
intervalFrames++;
if (intervalFrames > 30) {
intervalFrames = 1;
}
else if (intervalFrames != 1) {
//CMSampleBufferInvalidate(sampleBuffer);
return;
}
// Need to initialize start session time.
if (writtenFrames < 1) {
if (useNativeTime) imageSourceTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
else imageSourceTime = CMTimeMake( 0 * 20 ,600); //CMTimeMake(1,30);
[outputWriter startSessionAtSourceTime: imageSourceTime];
NSLog(@"Starting CMtime");
CMTimeShow(imageSourceTime);
}
if (useNativeTime) {
imageSourceTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
CMTimeShow(imageSourceTime);
// CMTime myTiming = CMTimeMake(writtenFrames * 20,600);
// CMSampleBufferSetOutputPresentationTimeStamp(sampleBuffer, myTiming); // Tried but has no affect.
appendSuccessFlag = [inputWriterBuffer appendSampleBuffer:sampleBuffer];
}
else {
CMSampleBufferRef newSampleBuffer;
CMSampleTimingInfo sampleTimingInfo;
sampleTimingInfo.duration = CMTimeMake(20,600);
sampleTimingInfo.presentationTimeStamp = CMTimeMake( (writtenFrames + 0) * 20,600);
sampleTimingInfo.decodeTimeStamp = kCMTimeInvalid;
OSStatus myStatus;
//NSLog(@"numSamples of sampleBuffer: %i", CMSampleBufferGetNumSamples(sampleBuffer) );
myStatus = CMSampleBufferCreateCopyWithNewTiming(kCFAllocatorDefault,
sampleBuffer,
1,
&sampleTimingInfo, // maybe a little confused on this param.
&newSampleBuffer);
// These confirm the good heath of our newSampleBuffer.
if (myStatus != 0) NSLog(@"CMSampleBufferCreateCopyWithNewTiming() myStatus: %i",myStatus);
if (! CMSampleBufferIsValid(newSampleBuffer)) NSLog(@"CMSampleBufferIsValid NOT!");
// No affect.
//myStatus = CMSampleBufferMakeDataReady(newSampleBuffer); // How is this different; CMSampleBufferSetDataReady ?
//if (myStatus != 0) NSLog(@"CMSampleBufferMakeDataReady() myStatus: %i",myStatus);
imageSourceTime = CMSampleBufferGetPresentationTimeStamp(newSampleBuffer);
CMTimeShow(imageSourceTime);
appendSuccessFlag = [inputWriterBuffer appendSampleBuffer:newSampleBuffer];
//CMSampleBufferInvalidate(sampleBuffer); // Docs don't describe action. WTF does it do? Doesn't seem to affect my problem. Used with CMSampleBufferSetInvalidateCallback maybe?
//CFRelease(sampleBuffer); // - Not surprisingly - “EXC_BAD_ACCESS”
}
if (!appendSuccessFlag)
{
NSLog(@"Failed to append pixel buffer");
}
else {
writtenFrames++;
NSLog(@"writtenFrames: %i", writtenFrames);
}
}
//[self displayOuptutWritterStatus]; // Expect and see AVAssetWriterStatusWriting.
}
我的安装程序。
- (IBAction) recordingStartStop: (id) sender
{
NSError * error;
if (self.isRecording) {
NSLog(@"~~~~~~~~~ STOPPING RECORDING ~~~~~~~~~");
self.isRecording = NO;
[recordingStarStop setTitle: @"Record" forState: UIControlStateNormal];
//[self.captureSession stopRunning];
[inputWriterBuffer markAsFinished];
[outputWriter endSessionAtSourceTime:imageSourceTime];
[outputWriter finishWriting]; // Blocks until file is completely written, or an error occurs.
NSLog(@"finished CMtime");
CMTimeShow(imageSourceTime);
// Really, I should loop through the outputs and close all of them or target specific ones.
// Since I'm only recording video right now, I feel safe doing this.
[self.captureSession removeOutput: [[self.captureSession outputs] objectAtIndex: 0]];
[videoOutput release];
[inputWriterBuffer release];
[outputWriter release];
videoOutput = nil;
inputWriterBuffer = nil;
outputWriter = nil;
NSLog(@"~~~~~~~~~ STOPPED RECORDING ~~~~~~~~~");
NSLog(@"Calling UIVideoAtPathIsCompatibleWithSavedPhotosAlbum.");
NSLog(@"filePath: %@", [projectPaths movieFilePath]);
if (UIVideoAtPathIsCompatibleWithSavedPhotosAlbum([projectPaths movieFilePath])) {
NSLog(@"Calling UISaveVideoAtPathToSavedPhotosAlbum.");
UISaveVideoAtPathToSavedPhotosAlbum ([projectPaths movieFilePath], self, @selector(video:didFinishSavingWithError: contextInfo:), nil);
}
NSLog(@"~~~~~~~~~ WROTE RECORDING to PhotosAlbum ~~~~~~~~~");
}
else {
NSLog(@"~~~~~~~~~ STARTING RECORDING ~~~~~~~~~");
projectPaths = [[ProjectPaths alloc] initWithProjectFolder: @"TestProject"];
intervalFrames = 30;
videoOutput = [[AVCaptureVideoDataOutput alloc] init];
NSMutableDictionary * cameraVideoSettings = [[[NSMutableDictionary alloc] init] autorelease];
NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey;
NSNumber* value = [NSNumber numberWithUnsignedInt: kCVPixelFormatType_32BGRA]; //kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange];
[cameraVideoSettings setValue: value forKey: key];
[videoOutput setVideoSettings: cameraVideoSettings];
[videoOutput setMinFrameDuration: CMTimeMake(20, 600)]; //CMTimeMake(1, 30)]; // 30fps
[videoOutput setAlwaysDiscardsLateVideoFrames: YES];
queue = dispatch_queue_create("cameraQueue", NULL);
[videoOutput setSampleBufferDelegate: self queue: queue];
dispatch_release(queue);
NSMutableDictionary *outputSettings = [[[NSMutableDictionary alloc] init] autorelease];
[outputSettings setValue: AVVideoCodecH264 forKey: AVVideoCodecKey];
[outputSettings setValue: [NSNumber numberWithInt: 1280] forKey: AVVideoWidthKey]; // currently assuming
[outputSettings setValue: [NSNumber numberWithInt: 720] forKey: AVVideoHeightKey];
NSMutableDictionary *compressionSettings = [[[NSMutableDictionary alloc] init] autorelease];
[compressionSettings setValue: AVVideoProfileLevelH264Main30 forKey: AVVideoProfileLevelKey];
//[compressionSettings setValue: [NSNumber numberWithDouble:1024.0*1024.0] forKey: AVVideoAverageBitRateKey];
[outputSettings setValue: compressionSettings forKey: AVVideoCompressionPropertiesKey];
inputWriterBuffer = [AVAssetWriterInput assetWriterInputWithMediaType: AVMediaTypeVideo outputSettings: outputSettings];
[inputWriterBuffer retain];
inputWriterBuffer.expectsMediaDataInRealTime = YES;
outputWriter = [AVAssetWriter assetWriterWithURL: [projectPaths movieURLPath] fileType: AVFileTypeQuickTimeMovie error: &error];
[outputWriter retain];
if (error) NSLog(@"error for outputWriter = [AVAssetWriter assetWriterWithURL:fileType:error:");
if ([outputWriter canAddInput: inputWriterBuffer]) [outputWriter addInput: inputWriterBuffer];
else NSLog(@"can not add input");
if (![outputWriter canApplyOutputSettings: outputSettings forMediaType:AVMediaTypeVideo]) NSLog(@"ouptutSettings are NOT supported");
if ([captureSession canAddOutput: videoOutput]) [self.captureSession addOutput: videoOutput];
else NSLog(@"could not addOutput: videoOutput to captureSession");
//[self.captureSession startRunning];
self.isRecording = YES;
[recordingStarStop setTitle: @"Stop" forState: UIControlStateNormal];
writtenFrames = 0;
imageSourceTime = kCMTimeZero;
[outputWriter startWriting];
//[outputWriter startSessionAtSourceTime: imageSourceTime];
NSLog(@"~~~~~~~~~ STARTED RECORDING ~~~~~~~~~");
NSLog (@"recording to fileURL: %@", [projectPaths movieURLPath]);
}
NSLog(@"isRecording: %@", self.isRecording ? @"YES" : @"NO");
[self displayOuptutWritterStatus];
}
答案 0 :(得分：10)
好的，我在第一篇文章中发现了这个错误。
使用时
myStatus = CMSampleBufferCreateCopyWithNewTiming(kCFAllocatorDefault,
sampleBuffer,
1,
&sampleTimingInfo,
&newSampleBuffer);
您需要与CFRelease(newSampleBuffer);
将CVPixelBufferRef与AVAssetWriterInputPixelBufferAdaptor实例的piexBufferPool一起使用时，同样的想法也适用。调用CVPixelBufferRelease(yourCVPixelBufferRef);方法后，您将使用appendPixelBuffer: withPresentationTime:。
希望这对其他人有帮助。
答案 1 :(得分：3)
通过更多的搜索和阅读，我有一个有效的解决方案。不知道这是最好的方法，但到目前为止，还不错。
在我的设置区域中，我设置了AVAssetWriterInputPixelBufferAdaptor。代码添加看起来像这样。
InputWriterBufferAdaptor = [AVAssetWriterInputPixelBufferAdaptor
assetWriterInputPixelBufferAdaptorWithAssetWriterInput: inputWriterBuffer
sourcePixelBufferAttributes: nil];
[inputWriterBufferAdaptor retain];
为了完整理解下面的代码，我在设置方法中也有这三行。
fpsOutput = 30; //Some possible values: 30, 10, 15 24, 25, 30/1.001 or 29.97;
cmTimeSecondsDenominatorTimescale = 600 * 100000; //To more precisely handle 29.97.
cmTimeNumeratorValue = cmTimeSecondsDenominatorTimescale / fpsOutput;
而不是将重定时应用于样本缓冲区的副本。我现在有以下三行代码可以有效地执行相同的操作。请注意适配器的withPresentationTime参数。通过将我的自定义值传递给我，我获得了正确的时间。
CVPixelBufferRef myImage = CMSampleBufferGetImageBuffer( sampleBuffer );
imageSourceTime = CMTimeMake( writtenFrames * cmTimeNumeratorValue, cmTimeSecondsDenominatorTimescale);
appendSuccessFlag = [inputWriterBufferAdaptor appendPixelBuffer: myImage withPresentationTime: imageSourceTime];
使用AVAssetWriterInputPixelBufferAdaptor.pixelBufferPool属性可能会有一些收获，但我还没有想到这一点。