如何使用 AVAssetExportSession 导出 AVPlayer 音频 mp3 文件？

Question

I am now trying to export an mp3 file that has been player using AVPlayer (using an url) so it doesn't have to be downloaded twice.

This is my sample code:

I've tried every outputFileType...

    self.exporter = [[AVAssetExportSession alloc] initWithAsset:self.asset presetName:AVAssetExportPresetPassthrough];
        }

        NSError *error;

        NSLog(@"export.supportedFileTypes : %@",self.exporter.supportedFileTypes);
       //        "com.apple.quicktime-movie",
//        "com.apple.m4a-audio",
//        "public.mpeg-4",
//        "com.apple.m4v-video",
//        "public.3gpp",
//        "org.3gpp.adaptive-multi-rate-audio",
//        "com.microsoft.waveform-audio",
//        "public.aiff-audio",
//        "public.aifc-audio",
//        "com.apple.coreaudio-format"

        self.exporter.outputFileType = @"public.aiff-audio";
        self.exporter.shouldOptimizeForNetworkUse = YES;

        NSURL *a = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:YES error:&error];

        NSURL *url = [a URLByAppendingPathComponent:@"filename.mp3"];

        NSString *filePath = [url absoluteString];

        self.exporter.outputURL = url;

        if (![[NSFileManager defaultManager] fileExistsAtPath:filePath]){
            [self.exporter exportAsynchronouslyWithCompletionHandler:^{

                if (self.exporter.status == AVAssetExportSessionStatusCompleted)
                {

                    if (![[NSFileManager defaultManager] fileExistsAtPath:filePath]){
                        NSLog(@"File doesn't exist at path");
                    }else {
                        NSLog@"File saved!");
}                    
                }
                else if(self.exporter.status == AVAssetExportSessionStatusFailed){
                    NSLog(@"Failed");
                }else if(self.exporter.status == AVAssetExportSessionStatusUnknown){
                    NSLog(@"Unknown");
                }else if(self.exporter.status == AVAssetExportSessionStatusCancelled){
                    NSLog(@"Cancelled");
                }else if(self.exporter.status == AVAssetExportSessionStatusWaiting){
                    NSLog(@"Waiting");
                }else if(self.exporter.status == AVAssetExportSessionStatusExporting){
                    NSLog(@"Exporting");
                }

                NSLog(@"Exporter error! : %@",self.exporter.error);

              }];

        }}else{
            NSLog(@"File already exists at path");
        }

If this is not possible to accomplish, is there any work around?

Also, as I can change the format of the audio file. What's the ideal type to work with AVAudioPlayer?

Answer 1

It appears AVAssetExportSession only supports filetypes for mp3 transcoding with com.apple.quicktime-movie (.mov) and com.apple.coreaudio-format (.caf) using the AVAssetExportPresetPassthrough preset. You must also be sure to use one of these file extensions when writing your output file otherwise it won't save.

Supported output filetype and extensions for an mp3 input file are in bold (tested on OS X 10.11.6):

• com.apple.quicktime-movie (.mov)
• com.apple.m4a-audio (.m4a)
• public.mpeg-4 (.mp4)
• com.apple.m4v-video (.m4v)
• org.3gpp.adaptive-multi-rate-audio (.amr)
• com.microsoft.waveform-audio (.wav)
• public.aiff-audio (.aiff)
• public.aifc-audio (.aifc)
• com.apple.coreaudio-format (.caf)

If you don't mind performing a proper transcode of the audio data to another format, then you don't have to use the AVAssetExportPresetPassthrough preset. There are also AVAssetExportPresetLowQuality , AVAssetExportPresetMediumQuality , and AVAssetExportPresetHighestQuality . In the sample code that follows, the output URL has extension .m4a and the resulting transcode plays in iTunes and other media players:

AVAsset * asset = [AVAsset assetWithURL:inputURL];
AVAssetExportSession * exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality];
exportSession.outputFileType = AVFileTypeMPEG4;
exportSession.outputURL = outputURL;
exportSession.metadata = asset.metadata;       
[exportSession exportAsynchronouslyWithCompletionHandler:^{

    if (exportSession.status == AVAssetExportSessionStatusCompleted)
    {
            NSLog(@"AV export succeeded.");
    }
    else if (exportSession.status == AVAssetExportSessionStatusCancelled)
    {
        NSLog(@"AV export cancelled.");
    }
    else
    {
        NSLog(@"AV export failed with error: %@ (%ld)", exportSession.error.localizedDescription, (long)exportSession.error.code);
    }
}];

Answer 2

I tried to export audio file with mp3 format from ipod library. and this is my solution below.

extension DirectoryListViewController: MPMediaPickerControllerDelegate {
public func mediaPicker(_ mediaPicker: MPMediaPickerController, didPickMediaItems mediaItemCollection: MPMediaItemCollection) {
    guard let mediaItem = mediaItemCollection.items.first else { ImportExternalFileService.shared.alertImportError(); return  }
    guard let url = mediaItem.assetURL else { ImportExternalFileService.shared.alertImportError(); return }
    guard let songTitle = mediaItem.title else { ImportExternalFileService.shared.alertImportError(); return }
    guard let exportSession = AVAssetExportSession(asset: AVURLAsset(url: url), presetName: AVAssetExportPresetAppleM4A) else {
        ImportExternalFileService.shared.alertImportError(); return
    }
    exportSession.outputFileType = .m4a
    exportSession.metadata = AVURLAsset(url: url).metadata
    exportSession.shouldOptimizeForNetworkUse = true
    guard let fileExtension = UTTypeCopyPreferredTagWithClass(exportSession.outputFileType!.rawValue as CFString, kUTTagClassFilenameExtension) else {
        ImportExternalFileService.shared.alertImportError(); return
    }
    let documentURL = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
    let outputURL = documentURL.appendingPathComponent("\(songTitle).\(fileExtension.takeUnretainedValue())")
    /* Dont't forget to remove the existing url, or exportSession will throw error: can't save file */
    do {
        try FileManager.default.removeItem(at: outputURL)
    } catch let error as NSError {
        print(error.debugDescription)
    }
    exportSession.outputURL = outputURL
    exportSession.exportAsynchronously(completionHandler: {
        if exportSession.status == .completed {
            DispatchQueue.main.async {
                ImportExternalFileService.shared.importRecordFile(url: exportSession.outputURL!)
            }
        } else {
            print("AV export failed with error:- ", exportSession.error!.localizedDescription)
        }
    })
}

public func mediaPickerDidCancel(_ mediaPicker: MPMediaPickerController) {
    dismiss(animated: true, completion: nil)
}

}

Answer 3

You can't, but you can export m4a.

AVAssetExportSession *exportSession = [AVAssetExportSession exportSessionWithAsset:audioAsset presetName:AVAssetExportPresetAppleM4A];
exportSession.outputURL = [NSURL fileURLWithPath:exportPath];
exportSession.outputFileType = AVFileTypeAppleM4A;
[exportSession exportAsynchronouslyWithCompletionHandler:^{

}];