如何用AVAssetWriter写一部有视频和音频的电影？
我想用AVAssetWriter导出电影，但不知道如何同步包含视频和音频曲目。只导出视频效果很好，但当我添加音频时，结果电影如下所示：
首先我看到视频(没有音频)，然后视频冻结(显示最后一个图像帧直到结束)，几秒钟后我听到音频。
我尝试了一些CMSampleBufferSetOutputPresentationTimeStamp (从当前音频中减去第一个CMSampleBufferGetPresentationTimeStamp )的方法，但都不起作用，我认为这不是正确的方向，因为源电影中的视频和音频无论如何都应该是同步的……
我的设置简而言之:我创建一个AVAssetReader和2个AVAssetReaderTrackOutput (一个用于视频，一个用于音频)并将它们添加到AVAssetReader中，然后我创建一个AVAssetWriter和2个AVAssetWriterInput (视频和音频)并将它们添加到AVAssetWriter中……我从以下几个方面开始：
[assetReader startReading];
[assetWriter startWriting];
[assetWriter startSessionAtSourceTime:kCMTimeZero];然后我运行两个队列来做样本缓冲区的事情：
dispatch_queue_t queueVideo=dispatch_queue_create("assetVideoWriterQueue", NULL);
[assetWriterVideoInput requestMediaDataWhenReadyOnQueue:queueVideo usingBlock:^
{
while([assetWriterVideoInput isReadyForMoreMediaData])
{
CMSampleBufferRef sampleBuffer=[assetReaderVideoOutput copyNextSampleBuffer];
if(sampleBuffer)
{
[assetWriterVideoInput appendSampleBuffer:sampleBuffer];
CFRelease(sampleBuffer);
} else
{
[assetWriterVideoInput markAsFinished];
dispatch_release(queueVideo);
videoFinished=YES;
break;
}
}
}];
dispatch_queue_t queueAudio=dispatch_queue_create("assetAudioWriterQueue", NULL);
[assetWriterAudioInput requestMediaDataWhenReadyOnQueue:queueAudio usingBlock:^
{
while([assetWriterAudioInput isReadyForMoreMediaData])
{
CMSampleBufferRef sampleBuffer=[assetReaderAudioOutput copyNextSampleBuffer];
if(sampleBuffer)
{
[assetWriterAudioInput appendSampleBuffer:sampleBuffer];
CFRelease(sampleBuffer);
} else
{
[assetWriterAudioInput markAsFinished];
dispatch_release(queueAudio);
audioFinished=YES;
break;
}
}
}];在主循环中，我等待两个队列，直到它们完成：
while(!videoFinished && !audioFinished)
{
sleep(1);
}
[assetWriter finishWriting];此外，我尝试使用以下代码将结果文件保存在库中...
NSURL *url=[[NSURL alloc] initFileURLWithPath:path];
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
if([library videoAtPathIsCompatibleWithSavedPhotosAlbum:url])
{
[library writeVideoAtPathToSavedPhotosAlbum:url completionBlock:^(NSURL *assetURL, NSError *error)
{
if(error)
NSLog(@"error=%@",error.localizedDescription);
else
NSLog(@"completed...");
}];
} else
NSLog(@"error, video not saved...");
[library release];
[url release];...but我得到了这个错误：
Video /Users/cb/Library/Application Support/iPhone Simulator/4.2/Applications/E9865BF9-D190-4912-9248-66768B1AB635/Documents/export.mp4 cannot be saved to the saved photos album: Error Domain=NSOSStatusErrorDomain Code=-12950 "Movie could not be played." UserInfo=0x5e4fb90 {NSLocalizedDescription=Movie could not be played.}
代码在另一个程序中运行时没有任何问题。所以这部电影出了什么问题...？
回答 2
Stack Overflow用户
发布于 2013-10-19 17:58:34
-(void)mergeAudioVideo
{
NSString *videoOutputPath=[_documentsDirectory stringByAppendingPathComponent:@"dummy_video.mp4"];
NSString *outputFilePath = [_documentsDirectory stringByAppendingPathComponent:@"final_video.mp4"];
if ([[NSFileManager defaultManager]fileExistsAtPath:outputFilePath])
[[NSFileManager defaultManager]removeItemAtPath:outputFilePath error:nil];
NSURL *outputFileUrl = [NSURL fileURLWithPath:outputFilePath];
NSString *filePath = [_documentsDirectory stringByAppendingPathComponent:@"newFile.m4a"];
AVMutableComposition* mixComposition = [AVMutableComposition composition];
NSURL *audio_inputFileUrl = [NSURL fileURLWithPath:filePath];
NSURL *video_inputFileUrl = [NSURL fileURLWithPath:videoOutputPath];
CMTime nextClipStartTime = kCMTimeZero;
AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:video_inputFileUrl options:nil];
CMTimeRange video_timeRange = CMTimeRangeMake(kCMTimeZero,videoAsset.duration);
AVMutableCompositionTrack *a_compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[a_compositionVideoTrack insertTimeRange:video_timeRange ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];
AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:audio_inputFileUrl options:nil];
CMTimeRange audio_timeRange = CMTimeRangeMake(kCMTimeZero, audioAsset.duration);
AVMutableCompositionTrack *b_compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[b_compositionAudioTrack insertTimeRange:audio_timeRange ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:nextClipStartTime error:nil];
AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetMediumQuality];
_assetExport.outputFileType = @"com.apple.quicktime-movie";
_assetExport.outputURL = outputFileUrl;
[_assetExport exportAsynchronouslyWithCompletionHandler:
^(void ) {
if (_assetExport.status == AVAssetExportSessionStatusCompleted) {
//Write Code Here to Continue
}
else {
//Write Fail Code here
}
}
];
}您可以使用此代码来合并音频和视频。
Stack Overflow用户
发布于 2013-06-17 15:57:59
它认为assetWriterAudioInput忽略了音频写入的采样缓冲时间。这样做。
1)写入视频轨道。
2)完成后，将其标记为完成，即videoWriterInput markAsFinished；
3)执行assetWriter startSessionAtSourceTime:timeRangeStart；
3)实例化音频阅读器，开始写入音频。
https://stackoverflow.com/questions/5481268
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