我正在使用 AVAssetWriter
和 captureOutput
回调录制视频+音频。问题是,在大约 5% 的情况下,我无法从第二个零生成缩略图(如果我尝试在视频中走得更远,那么就没有问题)。我得到的错误是:
Error Domain=AVFoundationErrorDomain Code=-11832 "Cannot Open" UserInfo=0x4b31b0 {NSLocalizedFailureReason=This media cannot be used., NSUnderlyingError=0x4effb0 "The operation couldn’t be completed. (OSStatus error -12431.)", NSLocalizedDescription=Cannot Open}
这是我使用的代码:
AVURLAsset *asset=[[AVURLAsset alloc] initWithURL:url options:nil];
AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
generator.appliesPreferredTrackTransform=TRUE;
[asset release];
CMTime thumbTime = CMTimeMakeWithSeconds(0,30);
AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error)
{
if (result != AVAssetImageGeneratorSucceeded)
{
[self NSLogPrint:[NSString stringWithFormat:@"couldn't generate thumbnail, error:%@", error]];
}
UIImage *thumbImg=[[UIImage imageWithCGImage:im] retain];
[image setImage:thumbImg];
[thumbImg release];
[generator release];
};
CGSize maxSize = CGSizeMake(177, 100);
generator.maximumSize = maxSize;
[generator generateCGImagesAsynchronouslyForTimes:[NSArray arrayWithObject:[NSValue valueWithCMTime:thumbTime]] completionHandler:handler];
下面是我如何设置我的视频 AVAssetWriterInput:
- (BOOL) setupAssetWriterVideoInput:(CMFormatDescriptionRef)currentFormatDescription
{
float bitsPerPixel;
CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions(currentFormatDescription);
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 = 11.04; // This bitrate matches the quality produced by AVCaptureSessionPresetHigh.
bitsPerSecond = numPixels * bitsPerPixel;
NSDictionary *videoCompressionSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoCodecH264, AVVideoCodecKey,
[NSNumber numberWithInteger:dimensions.width], AVVideoWidthKey,
[NSNumber numberWithInteger:dimensions.height], AVVideoHeightKey,
[NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInteger:bitsPerSecond], AVVideoAverageBitRateKey,
[NSNumber numberWithInteger:30], AVVideoMaxKeyFrameIntervalKey,
nil], AVVideoCompressionPropertiesKey,
nil];
if ([_videoWriter canApplyOutputSettings:videoCompressionSettings forMediaType:AVMediaTypeVideo])
{
self._videoWriterInput = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo outputSettings:videoCompressionSettings];
self._videoWriterInput.expectsMediaDataInRealTime = YES;
self._videoWriterInput.transform = [self returnOrientation];
if ([_videoWriter canAddInput:self._videoWriterInput])
[_videoWriter addInput:self._videoWriterInput];
else
{
NSLog(@"Couldn't add asset writer video input.");
return NO;
}
}
else
{
NSLog(@"Couldn't apply video output settings.");
return NO;
}
return YES;
}
我知道错误是当时没有图像,但为什么会这样?
我还使用 AVCaptureMovieFileOutput 测试了录制,并且始终会生成缩略图。 此外,如果我将视频导出到相机胶卷,则预览也无法在照片中使用。
P.S:我也在某处读到这可能与关键帧间隔有关,但我不确定如何。
最佳答案
我有点解决了我的问题。我在 iOS 4.2.1 上运行,并决定升级到 iOS 5.1.1,问题消失了。
关于iphone - 从使用 AVAssetWriter 创建的视频生成缩略图,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/11485608/