使用Apple音频文件流服务，iOS 7，无法解析M4A，AAC文件 [英] Fail Parsing M4A, AAC file with Apple Audio File Stream Services, iOS 7

问题描述

我正在使用本教程

但如果您使用lets say encoding.com对m4a文件进行编码，您将获得不同类型的编码。

它们在从磁盘播放整个文件时都能正常工作，但优化版本将被正确解析/流式传输。

现在你得到的错误告诉你，解析器无法从你正在解析的文件中获取正确的 AudioStreamBasicDescription ，文件可能拒绝提供比特率信息...

尝试查看此代码以更好地理解处理m4a类型 http://www.cocoawithlove.com/2010/03/streaming-mp3aac-audio-again.html

I'm using this tutorial Multipeer Connectivity Audio Stream To Multiple Peers and this project Github Repository , in order to stream audio from NSInputStream, which is obtained by:

-(void)session:didReceiveStream:withName:fromPeer:

MCSession delegate method.

After, this open a new Audio File Stream (TDAudioFileStreamer/Classes/AudioFileStream.m:39):

OSStatus err = AudioFileStreamOpen((__bridge void *)self, TDAudioFileStreamPropertyListener, TDAudioFileStreamPacketsListener, 0, &_audioFileStreamID); 

Then read bytes from NSInputStream and try to parse by this way (TDAudioFileStreamer/Classes/AudioFileStream.m:98):

err = AudioFileStreamParseBytes(self.audioFileStreamID, length, data, kAudioFileStreamParseFlag_Discontinuity);

Or:

err = AudioFileStreamParseBytes(self.audioFileStreamID, length, data, 0);

Depending of the data flow.

And finally, this fill AudioQueue Buffer with the parsed data in order to playback (i guess - TDAudioFileStreamer/Classes/TDAudioQueueFiller.m) .

This works really nice for MP3 format files, but with others formats when try to parse the bytes get "unsupported file format" error.

The Apple documentation, says Audio File Stream services support a lot of formats and they are listed in this Link: Apple Stream Services supported formats, but for me only works with MP3.

I was trying too, when open the Audio File Stream pass a hint about file format like this and send a M4A or AAC file:

OSStatus err = AudioFileStreamOpen((__bridge void *)self, TDAudioFileStreamPropertyListener, TDAudioFileStreamPacketsListener, kAudioFileAAC_ADTSType, &_audioFileStreamID);

Where kAudioFileAAC_ADTSType is the type of sent file that will be streamed, by this way , the "unsupported file format error" disappears , but the application crashes and get a new error

This says: io: lpc and client: aac.

• Someone know what this mean?
• The Queue is expecting AAC format file?
• Why LPCM( Linear Pulse Code Modulation), i'm sending M4A or AAC not LPCM?

Thanks in advance.

解决方案

In order stream/parse M4A with AudioFileStream, the m4a file needs to be optimized for streaming.

That means the header needs to be in the front of the file and has the correct information that will let your parser to do its job.

Some encoders will optimize the m4a for you, but some encoders wont. For example If you create an m4a file with itunes player, by simply right clicking and choosing "Create AAC Version", that will create an m4a file that is optimized for streaming.

You can check it by using http://ridiculousfish.com/hexfiend/

but if you use lets say encoding.com to encode your m4a files, you will get a different type of encoding.

they will both work when playing the whole file from disk but optimized version will be parsed/streamed correctly.

Now the error you are getting tells you that parser couldnt get the correct AudioStreamBasicDescription from the file you are parsing, file probably refuse to give the bitrate info...

Try to take a look at this code for better understanding handling m4a types http://www.cocoawithlove.com/2010/03/streaming-mp3aac-audio-again.html

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