我正在使用AVAssetWriterInputPixelBufferAdaptor使用AVAssetWriter编写MP4视频文件。
来源是来自UIImagePickerController的视频，可以从相机或资产库中新捕获。现在的质量是UIImagePickerControllerQualityTypeMedium。
有时候作家失败了。它的状态为AVAssetWriterStatusFailed，AVAssetWriter个对象的错误属性为：
Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed"
UserInfo=0xf5d8990 {NSLocalizedFailureReason=An unknown error occurred (-536870210),
NSUnderlyingError=0x4dd8e0 "The operation couldn’t be completed. (OSStatus error -536870210.)",
NSLocalizedDescription=The operation could not be completed
错误发生在代码运行的大约20％的时间。它似乎在iPhone 4 / 4S上比在iPhone 5上更频繁地失败。
如果源视频质量较高，也会更频繁地发生。 使用UIImagePickerControllerQualityTypeLow错误并不经常发生。 使用UIImagePickerControllerQualityTypeHigh，错误发生得更频繁。
我还注意到其他事情： 它似乎有点波澜。当它失败时，即使我删除了应用程序并重新安装它，以下运行也经常会失败。这让我想知道，我的程序是否泄漏了一些内存，即使应用程序被杀死，该内存是否仍然存活（甚至可能？）。
以下是我用来渲染视频的代码：
- (void)writeVideo
{
offlineRenderingInProgress = YES;
/* --- Writer Setup --- */
[locationQueue cancelAllOperations];
[self stopWithoutRewinding];
NSError *writerError = nil;
BOOL succes;
succes = [[NSFileManager defaultManager] removeItemAtURL:self.outputURL error:nil];
// DLog(@"Url: %@, succes: %i, error: %@", self.outputURL, succes, fileError);
writer = [AVAssetWriter assetWriterWithURL:self.outputURL fileType:(NSString *)kUTTypeQuickTimeMovie error:&writerError];
//writer.shouldOptimizeForNetworkUse = NO;
if (writerError) {
DLog(@"Writer error: %@", writerError);
return;
}
float bitsPerPixel;
CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions((__bridge CMVideoFormatDescriptionRef)([readerVideoOutput.videoTracks[0] formatDescriptions][0]));
int numPixels = dimensions.width * dimensions.height;
int bitsPerSecond;
// Assume that lower-than-SD resolutions are intended for streaming, and use a lower bitrate
if ( numPixels < (640 * 480) )
bitsPerPixel = 4.05; // This bitrate matches the quality produced by AVCaptureSessionPresetMedium or Low.
else
bitsPerPixel = 11.4; // This bitrate matches the quality produced by AVCaptureSessionPresetHigh.
bitsPerSecond = numPixels * bitsPerPixel;
NSDictionary *videoCompressionSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoCodecH264, AVVideoCodecKey,
[NSNumber numberWithFloat:videoSize.width], AVVideoWidthKey,
[NSNumber numberWithInteger:videoSize.height], AVVideoHeightKey,
[NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInteger:30], AVVideoMaxKeyFrameIntervalKey,
nil], AVVideoCompressionPropertiesKey,
nil];
writerVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoCompressionSettings];
writerVideoInput.transform = movie.preferredTransform;
writerVideoInput.expectsMediaDataInRealTime = YES;
[writer addInput:writerVideoInput];
NSDictionary *sourcePixelBufferAttributesDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:kCVPixelFormatType_32ARGB], kCVPixelBufferPixelFormatTypeKey, nil];
writerPixelAdaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerVideoInput
sourcePixelBufferAttributes:sourcePixelBufferAttributesDictionary];
BOOL couldStart = [writer startWriting];
if (!couldStart) {
DLog(@"Could not start AVAssetWriter!");
abort = YES;
[locationQueue cancelAllOperations];
return;
}
[self configureFilters];
CIContext *offlineRenderContext = [CIContext contextWithOptions:@{kCIContextUseSoftwareRenderer : @NO}];
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
if (!self.canEdit) {
[self createVideoReaderWithAsset:movie timeRange:CMTimeRangeFromTimeToTime(kCMTimeZero, kCMTimePositiveInfinity) forOfflineRender:YES];
} else {
[self createVideoReaderWithAsset:movie timeRange:CMTimeRangeWithNOVideoRangeInDuration(self.thumbnailEditView.range, movie.duration) forOfflineRender:YES];
}
CMTime startOffset = reader.timeRange.start;
DLog(@"startOffset: %llu", startOffset.value);
[self.thumbnailEditView removeFromSuperview];
// self.thumbnailEditView = nil;
[glLayer removeFromSuperlayer];
glLayer = nil;
[playerView removeFromSuperview];
playerView = nil;
glContext = nil;
[writerVideoInput requestMediaDataWhenReadyOnQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) usingBlock:^{
@try {
BOOL didWriteSomething = NO;
DLog(@"Preparing to write...");
while ([writerVideoInput isReadyForMoreMediaData]) {
if (abort) {
NSLog(@"Abort == YES");
[locationQueue cancelAllOperations];
[writerVideoInput markAsFinished];
videoConvertCompletionBlock(NO, writer.error.localizedDescription);
}
if (writer.status == AVAssetWriterStatusFailed) {
DLog(@"Writer.status: AVAssetWriterStatusFailed, error: %@", writer.error);
[[NSUserDefaults standardUserDefaults] setObject:[NSNumber numberWithInt:1] forKey:@"QualityOverride"];
[[NSUserDefaults standardUserDefaults] synchronize];
abort = YES;
[locationQueue cancelAllOperations];
videoConvertCompletionBlock(NO, writer.error.localizedDescription);
return;
DLog(@"Source file exists: %i", [[NSFileManager defaultManager] fileExistsAtPath:movie.URL.relativePath]);
}
DLog(@"Writing started...");
CMSampleBufferRef buffer = nil;
if (reader.status != AVAssetReaderStatusUnknown) {
if (reader.status == AVAssetReaderStatusReading) {
buffer = [readerVideoOutput copyNextSampleBuffer];
if (didWriteSomething == NO) {
DLog(@"Copying sample buffers...");
}
}
if (!buffer) {
[writerVideoInput markAsFinished];
DLog(@"Finished...");
CGColorSpaceRelease(colorSpace);
[self offlineRenderingDidFinish];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[writer finishWriting];
if (writer.error != nil) {
DLog(@"Error: %@", writer.error);
} else {
DLog(@"Succes!");
}
if (writer.status == AVAssetWriterStatusCompleted) {
videoConvertCompletionBlock(YES, nil);
}
else {
abort = YES;
videoConvertCompletionBlock(NO, writer.error.localizedDescription);
}
});
return;
}
didWriteSomething = YES;
}
else {
DLog(@"Still waiting...");
//Reader just needs a moment to get ready...
continue;
}
CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(buffer);
if (pixelBuffer == NULL) {
DLog(@"Pixelbuffer == NULL");
continue;
}
//DLog(@"Sample call back! Pixelbuffer: %lu", CVPixelBufferGetHeight(pixelBuffer));
//NSDictionary *options = [NSDictionary dictionaryWithObject:(__bridge id)CGColorSpaceCreateDeviceRGB() forKey:kCIImageColorSpace];
CIImage *ciimage = [CIImage imageWithCVPixelBuffer:pixelBuffer options:nil];
CIImage *outputImage = [self filteredImageWithImage:ciimage];
CVPixelBufferRef outPixelBuffer = NULL;
CVReturn status;
CFDictionaryRef empty; // empty value for attr value.
CFMutableDictionaryRef attrs;
empty = CFDictionaryCreate(kCFAllocatorDefault, // our empty IOSurface properties dictionary
NULL,
NULL,
0,
&kCFTypeDictionaryKeyCallBacks,
&kCFTypeDictionaryValueCallBacks);
attrs = CFDictionaryCreateMutable(kCFAllocatorDefault,
1,
&kCFTypeDictionaryKeyCallBacks,
&kCFTypeDictionaryValueCallBacks);
CFDictionarySetValue(attrs,
kCVPixelBufferIOSurfacePropertiesKey,
empty);
CFDictionarySetValue(attrs,
kCVPixelBufferCGImageCompatibilityKey,
(__bridge const void *)([NSNumber numberWithBool:YES]));
CFDictionarySetValue(attrs,
kCVPixelBufferCGBitmapContextCompatibilityKey,
(__bridge const void *)([NSNumber numberWithBool:YES]));
status = CVPixelBufferCreate(kCFAllocatorDefault, ciimage.extent.size.width, ciimage.extent.size.height, kCVPixelFormatType_32BGRA, attrs, &outPixelBuffer);
//DLog(@"Output image size: %f, %f, pixelbuffer height: %lu", outputImage.extent.size.width, outputImage.extent.size.height, CVPixelBufferGetHeight(outPixelBuffer));
if (status != kCVReturnSuccess) {
DLog(@"Couldn't allocate output pixelBufferRef!");
continue;
}
[offlineRenderContext render:outputImage toCVPixelBuffer:outPixelBuffer bounds:outputImage.extent colorSpace:colorSpace];
CMTime currentSourceTime = CMSampleBufferGetPresentationTimeStamp(buffer);
CMTime currentTime = CMTimeSubtract(currentSourceTime, startOffset);
CMTime duration = reader.timeRange.duration;
if (CMTIME_IS_POSITIVE_INFINITY(duration)) {
duration = movie.duration;
}
CMTime durationConverted = CMTimeConvertScale(duration, currentTime.timescale, kCMTimeRoundingMethod_Default);
float durationFloat = (float)durationConverted.value;
float progress = ((float) currentTime.value) / durationFloat;
//DLog(@"duration : %f, progress: %f", durationFloat, progress);
[self updateOfflineRenderProgress:progress];
if (pixelBuffer != NULL && writerVideoInput.readyForMoreMediaData) {
[writerPixelAdaptor appendPixelBuffer:outPixelBuffer withPresentationTime:currentTime];
} else {
continue;
}
if (writer.status == AVAssetWriterStatusWriting) {
DLog(@"Writer.status: AVAssetWriterStatusWriting");
}
CFRelease(buffer);
CVPixelBufferRelease(outPixelBuffer);
}
}
@catch (NSException *exception) {
DLog(@"Catching exception: %@", exception);
}
}];
}
答案 0 :(得分：13)
好的，我想我自己解决了。坏人就是这句话：
[writerVideoInput requestMediaDataWhenReadyOnQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) usingBlock:^{ ....
我传递的全局队列是并发队列。这允许在前一个回调完成之前进行新的回调。资产编写器不是设计为一次从多个线程写入。
创建和使用新的串行队列似乎可以解决问题：
assetWriterQueue = dispatch_queue_create("AssetWriterQueue", DISPATCH_QUEUE_SERIAL);
[writerVideoInput requestMediaDataWhenReadyOnQueue:assetWriterQueue usingBlock:^{...