iOS 视频到音频文件的转换

Question

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Answer 1

首先，您不想转换任何东西，那很慢。相反，您想从 mp4 文件中提取音频流。为此，您可以创建一个仅包含原始文件音轨的 AVMutableComposition，然后使用 AVAssetExportSession 导出组合。目前以 m4a 为中心。如果您想同时处理 m4a 和 mp3 输出，请检查音轨类型，确保设置正确的文件扩展名，并在导出 session 中选择 AVFileTypeMPEGLayer3 或 AVFileTypeAppleM4A。

    NSURL*      dstURL = [NSURL fileURLWithPath:dstPath];
    [[NSFileManager defaultManager] removeItemAtURL:dstURL error:nil];

    AVMutableComposition*   newAudioAsset = [AVMutableComposition composition];

    AVMutableCompositionTrack*  dstCompositionTrack;
    dstCompositionTrack = [newAudioAsset addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];


    AVAsset*    srcAsset = [AVURLAsset URLAssetWithURL:srcURL options:nil];
    AVAssetTrack*   srcTrack = [[srcAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];


    CMTimeRange timeRange = srcTrack.timeRange;

    NSError*    error;

    if(NO == [dstCompositionTrack insertTimeRange:timeRange ofTrack:srcTrack atTime:kCMTimeZero error:&error]) {
        NSLog(@"track insert failed: %@\n", error);
        return;
    }


    AVAssetExportSession*   exportSesh = [[AVAssetExportSession alloc] initWithAsset:newAudioAsset presetName:AVAssetExportPresetPassthrough];

    exportSesh.outputFileType = AVFileTypeAppleM4A;
    exportSesh.outputURL = dstURL;

    [exportSesh exportAsynchronouslyWithCompletionHandler:^{
        AVAssetExportSessionStatus  status = exportSesh.status;
        NSLog(@"exportAsynchronouslyWithCompletionHandler: %i\n", status);

        if(AVAssetExportSessionStatusFailed == status) {
            NSLog(@"FAILURE: %@\n", exportSesh.error);
        } else if(AVAssetExportSessionStatusCompleted == status) {
            NSLog(@"SUCCESS!\n");
        }
    }];