iOS视频到音频文件的转换

Question

我管理它使用NSUrlConnection下载YouTube视频并将其保存到设备.现在我想将此(我猜.mp4)文件转换为.mp3音频文件.有谁知道这个问题的解决方案？也许有办法只从视频中下载音频？这将节省大量时间.

Answer 1

首先,你不想转换任何东西,这很慢.而是想要从mp4文件中提取音频流.您可以通过创建AVMutableComposition仅包含原始文件的音轨,然后使用a导出合成来完成此操作AVAssetExportSession.这是目前以m4a为中心的.如果要同时处理M4A和MP3输出,检查音轨类型,一定要设置正确的文件扩展名之间进行选择AVFileTypeMPEGLayer3或AVFileTypeAppleM4A在出口会话.

    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");
        }
    }];