ios - 使用 AVAssetReaderVideoCompositionOutput 导出进行到一半，然后以 AVFoundationErrorDomain Code=-11800 退出

Question

我已经从 AVAssets 构建了一个 AVMutableComposition 和 VideoComposition 并且能够播放它。我也可以使用 AVAssetExportSession 导出它，但是 AVAssetExportSession 不提供对设置的太多控制，所以我使用 AVAssetReader/AVAssetWriter 导出它，但不幸的是我遇到了一个我不理解的错误并且只写了部分输出文件。

这是我目前的代码。我已经省略了编写器和尽可能多的其他内容(包括一些错误检查)，我认为这些内容与使代码更易于阅读无关，因为它很多。请注意，我还没有处理音轨——我正在尝试一次一个步骤地执行此操作，但也许这是我的问题？

变量 asset 是 AVMutableComposition。

// ------- reader
_assetReader = [AVAssetReader assetReaderWithAsset:asset error:error];

_assetReader.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);
_duration = asset.duration;

// --- video reader
NSArray *videoTracks = [asset tracksWithMediaType:AVMediaTypeVideo];

NSDictionary *videoOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];

_assetReaderOutput = [AVAssetReaderVideoCompositionOutput assetReaderVideoCompositionOutputWithVideoTracks:videoTracks
                                                                                             videoSettings:videoOptions];
((AVAssetReaderVideoCompositionOutput *)_assetReaderOutput).videoComposition = composition;
[_assetReader addOutput:_assetReaderOutput];


// -- leaving out the export settings and construction
//    of the assetWriter since that doesn't seem to be the issue


// -- here's the actual export:

[self.assetWriter startWriting];
[self.assetWriter startSessionAtSourceTime:kCMTimeZero];
[self.assetReader startReading];


CMSampleBufferRef buffer;


while ( [self.assetReader status]==AVAssetReaderStatusReading )
{
    if(![self.assetWriterInput isReadyForMoreMediaData])
        continue;

    buffer = [self.assetReaderOutput copyNextSampleBuffer];


    NSLog(@"READING");

    if(buffer)
        [self.assetWriterInput appendSampleBuffer:buffer];

    NSLog(@"WRITTING...");


}
if( self.assetReader.status == AVAssetReaderStatusFailed ) {
    NSLog( @"%@", self.assetReader.error ); //<--------- I get a problem here
}


//Finish the session:
[self.assetWriterInput markAsFinished];
[self.assetWriter finishWriting];
NSLog(@"Write Ended");

问题是循环在短时间后退出，我得到这个输出:

Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo=0x17f1dfa0 {NSLocalizedDescription=The operation could not be completed, NSUnderlyingError=0x191617f0 "The operation couldn’t be completed. (OSStatus error -308.)", NSLocalizedFailureReason=An unknown error occurred (-308)}

Answer 1

似乎我遵循了一些错误的示例代码，而不是苹果提供的正确示例代码，关于如何执行此操作非常清楚，即使非常冗长:

https://developer.apple.com/library/Mac/DOCUMENTATION/AudioVideo/Conceptual/AVFoundationPG/Articles/05_Export.html#//apple_ref/doc/uid/TP40010188-CH9-SW2

虽然我已经完全重写了我的代码，但我认为我遇到的具体问题是没有在从 [self.assetReaderOutput copyNextSampleBuffer] 返回的 CMSampleBufferRef 上调用 CFRelease。您需要在循环内执行此操作。