[mad-user] dual-thread libmad

[Steve Spano]

Hi John

Thanks for the reply.

I actually don't want any mixing at all. I want MP3(A) to be played on
channel A and MP3(B) to be played on channel B. Something is occurring,
which appears to be towards the output stage of my libmad, that is
causing the A and B samples to mix together. So I am looking for some
global buffer that is being using by both A and B or something like that
which the RTOS is mixing between both threads.

Steve Spano, President
Finger Lakes Engineering


-----Original Message-----
From: john cooper [mailto:john.cooper at third-harmonic.com] 
Sent: Saturday, December 08, 2007 9:04 AM
To: Steve Spano
Cc: mad-user at lists.mars.org
Subject: Re: [mad-user] dual-thread libmad

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