[mad-user] dual-thread libmad

[john cooper]

Steve Spano wrote:
> Hi John,
> 
> Thanks for the reply.
> 
> I did more tracking into this, the mad_decoder_buffer creates the
> instances on the frame/stream/sync data. I already created two instances
> of the mad_decoder_buffer so I could link them to each RTOS thread.
> 
> It looks like the samples are getting mixed up at the output stage. It
> turns out that one of the MP3s playing is a 1-channel and the other MP3
> is a 2-channel. Any thoughts perhaps on how mixing of sample data,
> between RTOS tasks, could occur on the output stages? 

You'll need to make output the data rates agree potentially
converting one to the other.  And you will need to
synchronize and mix the two streams before they hit the
audio device.  This should be relatively straightforward
but you may need to scale the data to avoid clipping during
the mix operation.

-john


> I figured this part out, that it is occurring at the output stage,
> Friday ~ 5pm. I have to look at it some more.
> 
> Thanks
> 
> Steve Spano, President
> Finger Lakes Engineering
> 
> 
> -----Original Message-----
> From: john cooper [mailto:john.cooper at third-harmonic.com] 
> Sent: Friday, December 07, 2007 10:09 AM
> To: Steve Spano
> Cc: mad-user at lists.mars.org; john cooper
> Subject: Re: [mad-user] dual-thread libmad
> 
> Steve Spano wrote:
> 
>> I have a simple RTOS which has two threads. Each thread starts lib mad
> 
>> with a dedicated mad_decoder buffer for each thread. I am now able to 
>> "read" data correcting into the decoders (i.e. I don't see decoding 
>> errors streaming everywhere on the debug trace) but the output audio
> is 
>> mixed up. Meaning that the audio from the two threads is being mixed 
>> (actually shuffled) during playback.
> 
> It is built into the API.  You'll need to keep separate
> frame/stream/synth data structures for each instance of
> a decode operation.  Sounds like you are rendering to the
> same set of structures multiplexed by the task scheduler.
> 
> -john
> 


-- 
john.cooper at third-harmonic.com