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Subject: Re: MPEG Audio format

Re: MPEG Audio format

From: Dave Chapman <dave_at_dchapman.com>
Date: 2006-01-14

Thom Johansen wrote:
> Bluechip wrote:
>
>> Pretty much got a proper core written for an Audio file processor now.
>>
>> I have another simple question about MPEG Audio files.
>>
>> Am I ever likely to encounter an MPEG Audio file which will contain
>> AUDIO frames which differ in VERSION, LAYER, SAMPLERATE and/or
>> CHANNELS? Eg. Some frames are 48KHz and other frames are 44.1KHz
>> ...or some frames in Stereo, some in Joint-Stereo?
>>
>> I have been unable to find any documentation which explicitly states
>> whether this should or shouldn't be allowed by the MPEG standard, and
>> nothing to say explicitly whether any players do or don't support this
>> type of change.
>
>
> When it comes to sample rate, layer and version switching, I think you're
> reasonably safe, though it is probably legal. Stereo mode I think you will
> find encoders may switch from frame to frame.

I can confirm that the stereo mode can vary between frames in the same
stream - every digital radio (layer-2) broadcast stream I've seen which
uses "joint stereo" frames also has some plain "stereo" frames mixed in.

I've never seen stereo and mono mixed together in the same stream, but
that obviously doesn't mean it's illegal.

Dave.
Received on Sat Jan 14 01:37:54 2006


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