如何使用 AVAssetWriter 编写带有视频和音频的电影？

Question

我想使用 AVAssetWriter 导出电影，但不知道如何同步包含视频和音频轨道。仅导出视频效果很好，但是当我添加音频时，生成的电影如下所示：

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。

我尝试使用 CMSampleBufferSetOutputPresentationTimeStamp （从当前减去第一个 CMSampleBufferGetPresentationTimeStamp）来获取音频，但这一切都不起作用，我不认为这是正确的方向，因为视频和无论如何，源电影中的音频应该同步...

我的设置简而言之：我创建一个 AVAssetReader 和 2 AVAssetReaderTrackOutput （一个用于视频，一个用于音频）并添加将它们添加到 AVAssetReader 中，然后创建一个 AVAssetWriter 和 2 AVAssetWriterInput （视频和音频）并将它们添加到 AVAssetWriter< /code>...我开始一切：

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

然后我运行 2 个队列来执行示例缓冲区内容：

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，我尝试将生成的文件保存在库中以下代码...

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];

...但我收到错误：

视频 /Users/cb/Library/Application Support/iPhone Simulator/4.2/Applications/E9865BF9-D190-4912-9248-66768B1AB635/Documents/export.mp4 无法保存到已保存的相册：错误 Domain=NSOSStatusErrorDomain Code=-12950“电影无法播放。” UserInfo=0x5e4fb90 {NSLocalizedDescription=电影无法播放 已播放。}

该代码在另一个程序中运行没有问题。那么这部电影有什么问题吗...？

Answer 1

-(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。

Answer 2

assetWriterAudioInput 似乎忽略了音频写入的样本缓冲时间。
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）实例化音频读取器并开始写入音频。