Question

因此,我面临一个非常令人厌恶和奇怪的问题,并想知道是否有其他人来处理这个问题。我从手机音乐图书馆获得MPMediaItem的原始数据,然后通过吉卜赛人协会将其送往其他地方。在我提出问题时,我是从一卷零4a号档案中收集原始数据,看来是遗漏的。例如,如果我从旁听的原始档案是7.4mb,那么从我的法典中发现的病情是7.3mb。我做了一些研究,发现一个m4a文档实际上是一种cap,我认为,我没有仅仅依靠原始音乐数据,因此无法辨认。我的守则给我提供了MPMediaItem的原始音乐数据。

                    NSError * error = nil;
                    MPMediaQuery *query = [MPMediaQuery albumsQuery];
                    NSArray * songs = query.items;  
                    MPMediaItem * song = [songs objectAtIndex:socket_data_index];  
                    AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:[song valueForProperty:MPMediaItemPropertyAssetURL] options:nil];
                    AVAssetReader * reader = [[AVAssetReader alloc] initWithAsset:songAsset error:&error];                  
                    AVAssetTrack * songTrack = [songAsset.tracks objectAtIndex:0];
                    AVAssetReaderTrackOutput * output = [[AVAssetReaderTrackOutput alloc] initWithTrack:songTrack outputSettings:nil];
                    [reader addOutput:output];                         
                    [output release]; 



                    [reader startReading];

                    while (reader.status == AVAssetReaderStatusReading)
                    {                            
                        AVAssetReaderTrackOutput * trackOutput = (AVAssetReaderTrackOutput *)[reader.outputs objectAtIndex:0];
                        CMSampleBufferRef sampleBufferRef = [trackOutput copyNextSampleBuffer];                            
                        if (sampleBufferRef)
                        {
                            CMBlockBufferRef blockBufferRef = CMSampleBufferGetDataBuffer(sampleBufferRef);

                            size_t length = CMBlockBufferGetDataLength(blockBufferRef);
                            NSMutableData * data = [[NSMutableData alloc] initWithLength:length];
                            CMBlockBufferCopyDataBytes(blockBufferRef, 0, length, data.mutableBytes);

                            [data_to_return appendData:data];
                            [data release];

                            CMSampleBufferInvalidate(sampleBufferRef);
                            CFRelease(sampleBufferRef);
                        }
                    }

                    if (reader.status == AVAssetReaderStatusFailed || reader.status == AVAssetReaderStatusUnknown)
                    {
                        // Something went wrong. Handle it.
                    }

                    if (reader.status == AVAssetReaderStatusCompleted)
                    {                         

                       return [[[HTTPDataResponse alloc] initWithData:data_to_return] autorelease];
                    }

                    [reader release];

我确实并且将获得有关电话图书馆的p.mp3文档的正确数据,但就m4a而言,似乎有些部分缺失。

再次感谢你们花时间帮助我。

Answer 1

我也遇到了同样的问题。 AVAssetReader只回收原始视听数据。由于档案格式只是一个包含所有参与者需要击退档案的 frames方。您可能注意到,出口档案中所有id3信息都缺失。

.m4a audio files are containers that wrap around aac audio data. You received only the audio data, without further information i.e. samplerate or the seek-table.

解决你的问题的办法是利用AVAssetExportSession将AVAssetTrack出口到电话档案中,并从那里将档案输入。我对此事进行了具体审理,并撰写了一份工作文件。

The following Code is based on 果树例子:如何出口三毫米的音频资产 :

// create the export session
AVAssetExportSession *exportSession = [AVAssetExportSession
                                       exportSessionWithAsset: songAsset
                                       presetName:AVAssetExportPresetAppleM4A];
if (nil == exportSession)
    NSLog(@"Error");

// configure export session  output with all our parameters
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;
NSString *filePath = [NSString stringWithFormat: @"%@/export.m4a", basePath];

exportSession.outputURL = [NSURL fileURLWithPath: filePath]; // output path
exportSession.outputFileType = AVFileTypeAppleM4A; // output file type

[exportSession exportAsynchronouslyWithCompletionHandler:^{
    if (AVAssetExportSessionStatusCompleted == exportSession.status)
    {
        NSLog(@"AVAssetExportSessionStatusCompleted");
    }
    else if (AVAssetExportSessionStatusFailed == exportSession.status)
    {
        // a failure may happen because of an event out of your control
        // for example, an interruption like a phone call comming in
        // make sure and handle this case appropriately
        NSLog(@"AVAssetExportSessionStatusFailed");
    }
    else
    {
        NSLog(@"Export Session Status: %d", exportSession.status);
    }
}];

解决办法的下部分是,文件必须放在软盘上。我仍在寻找更好的办法处理Mm4a档案。

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