Re: Getting wrong data format for stream

Subject: Re: Getting wrong data format for stream
From: james mccartney <email@hidden>
Date: Tue, 21 Jul 2009 18:06:03 -0700
Delivered-to: email@hidden
Delivered-to: email@hidden

Are you supplying a buffer whose first byte begins an MPEG Layer 3 packet (optionally preceeded by an ID3 tag), or is it a buffer that starts in the middle of some random header data after which, at some point, there is MP3 data. If the former, then the parser may be picking up on the first bytes that look like an MPEG packet header and reporting that as the format.

There is not really any way to start in the middle of random data and reliably determine the format. There have been some fixes in this area to improve reliability, but there is no certain method for deducing the format starting from a random position in a finite buffer of arbitrary data.


On Jul 21, 2009, at 2:03 PM, Tom Harrington wrote:

I'm using Audio File Stream Services to play streaming audio from a web site.

The stream in question is MP3, 44100Hz, 112kbps, from a shoutcast
server (more details on request).  When I create the stream I provide
a file type hint of kAudioFileMP3Type.

Periodically, maybe one out of 8 times, I get bogus data for
kAudioFileStreamProperty_DataFormat.  It'll have an incorrect sample
rate (usually 32000Hz or 48000Hz) and a format of MP1
(kAudioFormatMPEGLayer1).  Playback then fails-- since I'm on iPhone,
AudioQueueNewOutput() returns kAudioFormatUnknownFormatError.

I look up the format by waiting for
kAudioFileStreamProperty_ReadyToProducePackets and then doing:

AudioStreamBasicDescription dataFormat;
UInt32 propertySize = sizeof(AudioStreamBasicDescription);
OSStatus audioStatus = AudioFileStreamGetProperty(inAudioFileStream,
kAudioFileStreamProperty_DataFormat, &propertySize, &dataFormat);

When I get bogus data, audioStatus is 0, but the returned format is
bogus.  What can I do to deal with this?

--
Tom Harrington
email@hidden
AIM: atomicbird1
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Re: Getting wrong data format for stream
From: james mccartney <email@hidden>


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  >Getting wrong data format for stream (From: Tom Harrington <email@hidden>)




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References:
	>Getting wrong data format for stream (From: Tom Harrington <email@hidden>)