iphone - AVAssetExportSession 不导出音轨

Question

我有一个应用程序，允许附加多个视频资源并向合成添加一个或多个音轨。一切似乎都有效，我可以使用 AVPlayer 播放生成的作品(尽管音频级别似乎很低)。将乐曲导出到文件后，音轨丢失。

我的代码主要基于 WWDC10 session 中的 AVEditDemo 示例代码。我已经根据 AVEditDemo 代码仔细检查了我的代码，但找不到可能存在的问题。我也检查过论坛，但没有太多 AVFoundation 相关的帖子/解决方案。

非常欢迎任何帮助。干杯，

让-皮埃尔

<小时/>

使用额外音轨构建作品的方法

注释:

compositionArray:包含构建合成的资源。
AssetView:包含 AVURLAsset 的对象。

- (AVMutableComposition *)buildCompositionObjects
{
// no assets available, return nil
if ([compositionArray count] < 1)
{
    return nil;
}

// get the asset video size
AssetView * view =  [compositionArray objectAtIndex:0];
AVURLAsset * asset = view.asset;

CGSize videoSize = [asset naturalSize];

// create new composition
AVMutableComposition * cmp = [AVMutableComposition composition];

// set the size
cmp.naturalSize = videoSize;

// build composition
[self buildComposition:cmp];

// add any extra audio track
[self addAudioTrackToComposition:cmp];

// return the new composition
return cmp;
}

构建基础组合的方法

- (void) buildComposition:(AVMutableComposition *)cmp
{
// set the start time of contiguous tracks
CMTime nextClipStartTime = kCMTimeZero;

// clear the composition
[cmp removeTimeRange:CMTimeRangeMake(CMTimeMake(0, 600), cmp.duration)];

// add audio and video tracks
AVMutableCompositionTrack *compositionVideoTrack = [cmp addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableCompositionTrack *compositionAudioTrack = [cmp addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

// loop through all available assets
for (AssetView * view in compositionArray)
{
    AVURLAsset *asset = view.asset;

    CMTimeRange timeRangeInAsset;
    timeRangeInAsset = CMTimeRangeMake(kCMTimeZero, [asset duration]);

    AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    [compositionVideoTrack insertTimeRange:timeRangeInAsset ofTrack:clipVideoTrack atTime:nextClipStartTime error:nil];

    // make sure there is an audio track. Had to do this becaaause of this missing audio track issue. Crashes if check is not done  (out of bounds).
    if ([[asset tracksWithMediaType:AVMediaTypeAudio] count] > 0)
    {
        AVAssetTrack *clipAudioTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
        [compositionAudioTrack insertTimeRange:timeRangeInAsset ofTrack:clipAudioTrack atTime:nextClipStartTime error:nil];
    }

    // adjust next asset start
    nextClipStartTime = CMTimeAdd(nextClipStartTime, timeRangeInAsset.duration);
}
}

添加附加音轨的方法

- (void)addAudioTrackToComposition:(AVMutableComposition *)cmp
{
// no audio track, return
if ([audioTracks count] < 1)
{
    return;
}

// base track ID for additional audio tracks 
long baseTrackID = 100;

for (AVURLAsset * audioAsset in audioTracks)
{
    // make sure the audio track fits in the composition
    CMTimeRange commentaryTimeRange = CMTimeRangeMake(kCMTimeZero, audioAsset.duration);

    if (CMTIME_COMPARE_INLINE(CMTimeRangeGetEnd(commentaryTimeRange), >, [cmp duration]))
    {
        commentaryTimeRange.duration = CMTimeSubtract([cmp duration], commentaryTimeRange.start);
    }

    // Add the audio track.
    AVMutableCompositionTrack *compositionCommentaryTrack = [cmp addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:baseTrackID++];

    [compositionCommentaryTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, commentaryTimeRange.duration) ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:commentaryTimeRange.start error:nil];
}    

}

导出组合物的方法

- (void) save
{

NSString * eventFolder = [NSString stringWithFormat:@"%@/%@-%@", 
               DOCUMENTS_FOLDER, 
               event.title,
               [StringUtils stringForDate:event.timeStamp]];


NSString * exportVideoPath = [NSString stringWithFormat:@"%@/Edits/%@.MOV", eventFolder, [StringUtils stringForDate:[NSDate date]]];

video.path = exportVideoPath;

AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetHighestQuality];

NSURL *exportURL = [NSURL fileURLWithPath:exportVideoPath];
exportSession.outputURL = exportURL;
exportSession.outputFileType = AVFileTypeQuickTimeMovie;
[exportSession exportAsynchronouslyWithCompletionHandler:^
{
    switch (exportSession.status) 
    {
        case AVAssetExportSessionStatusFailed:
        {
            NSLog (@"FAIL");
            [self performSelectorOnMainThread:@selector (doPostExportFailed:)
                                   withObject:nil
                                waitUntilDone:NO];
            break;
        }
        case AVAssetExportSessionStatusCompleted: 
        {
            NSLog (@"SUCCESS");
            [self performSelectorOnMainThread:@selector (doPostExportSuccess:)
                                   withObject:nil
                                waitUntilDone:NO];
            break;
        }
        case AVAssetExportSessionStatusCancelled: 
        {
            NSLog (@"CANCELED");
            [self performSelectorOnMainThread:@selector (doPostExportCancelled:)
                                   withObject:nil
                                waitUntilDone:NO];
            break;
        }
    };
}];

}

Answer 1

没有得到任何回复。我通过添加一行代码就可以工作:

 exportSession.shouldOptimizeForNetworkUse = YES;

之前

[exportSession exportAsynchronouslyWithCompletionHandler:^

我不确定为什么这可以解决问题。因为这似乎与问题完全无关，但我能够毫无问题地导出十几个包含最多 5 个额外音轨的作品。

我希望这可以帮助其他几天来一直摸不着头脑的人。

干杯