objective-c - 为什么唯一可用的 AVAssetExportSession.outputFileType = AVFileTypeQuickTimeMovie

Question

我设置了一个 AVAssetExportSession，只有 2 个音频轨道，没有视频，它在 AVPlayer 中播放时就像我想要的那样 - 但是当我开始的时候要导出它，唯一可用的 outputFileType 是 AVFileTypeQuickTimeMovie - 为什么我不能选择音频格式？

当我 NSLog(@"%@", [session supportedFileTypes]); 我得到;

[51330:c07] (
    "com.apple.quicktime-movie"
)

这是我的代码；

- (AVMutableComposition *)getComposition {
    AVAsset *backingAsset = [AVAsset assetWithURL:self.urlForEightBarAudioFile];
    AVAsset *vocalsAsset = [AVAsset assetWithURL:self.recorder.url];
    AVMutableComposition *composition = [AVMutableComposition composition];
    AVMutableCompositionTrack *compositionBackingTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    AVMutableCompositionTrack *compositionVocalTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

    AVAssetTrack *backingAssetTrack = [backingAsset.tracks objectAtIndex:0];
    AVAssetTrack *vocalsAssetTrack = [vocalsAsset.tracks objectAtIndex:0];

    CMTimeRange timeRange = CMTimeRangeFromTimeToTime(kCMTimeZero, backingAsset.duration);

    [compositionBackingTrack insertTimeRange:timeRange ofTrack:backingAssetTrack atTime:kCMTimeZero error:nil];
    [compositionVocalTrack insertTimeRange:timeRange ofTrack:vocalsAssetTrack atTime:kCMTimeZero error:nil];

    return composition;
}


- (IBAction)acceptRecording:(id)sender {
    AVAssetExportSession * session = [[AVAssetExportSession alloc] initWithAsset:[self getComposition] presetName:AVAssetExportPresetMediumQuality];
    NSURL *output = [self.urlForPathToEightBarRecordings URLByAppendingPathComponent:@"mix.mov"];
    session.outputURL = output;
    session.outputFileType = AVFileTypeQuickTimeMovie;

    NSLog(@"%@", [session supportedFileTypes]);
    [session exportAsynchronouslyWithCompletionHandler:^() {
        switch (session.status) {
            case AVAssetExportSessionStatusCompleted:
                NSLog(@"It's done...hallelujah");
                break;

            default:
                break;
        }
    }];
}

Answer 1

啊对了所以它只给我 quicktime 电影选项的原因是因为我的预设设置为 AVAssetExportPresetMediumQuality 我猜这是一个视频预设。我将我的预设设置为 AVAssetExportPresetAppleM4A 并将输出文件类型设置为 AVFileTypeAppleM4A 并且导出成功!