[SDL] Crash in SDL_mixer post-mixing callback on x86 Mac running XP

Sun Apr 8 23:05:27 PDT 2007

Looks like no dice on the sampling frequency idea. I had him run
a new compile modified to print the information returned by
Mix_QuerySpec and it gives this:

Mix_QuerySpec: fmt=S16LSB, freq=44100, chans=2

This seems to be the same as the format requested in the call
to Mix_OpenAudio.  Thanks for the suggestion, however. It's
always useful to rule things out.

James

>From: "Ryan C. Gordon" <icculus at icculus.org>
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>Subject: Re: [SDL] Crash in SDL_mixer post-mixing callback on x86 Mac 
>running XP
>Date: Mon, 09 Apr 2007 00:57:06 -0400
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>James Haley wrote:
> > The sound code of my Doom port, the Eternity Engine, is crashing
> > for one of my users who is running XP on an x86 Mac machine. When
> > compiled using SDL 1.2.10 and SDL_mixer 1.2.7, the program suffers
> > a crash at a seemingly arbitrary point within the post-mix callback
> > function. The game actually remains playable, but the standard
> > Windows error report dialog appears over the screen and the sound
> > begins to constantly repeat the last bytes of sound played. When
> > compiled with SDL 1.2.11, the main game thread also locks up.
> >
> > The application error reported is 0xc0000005 (a memory access error
> > according to MSDN).
> >
> > Here is a screenshot of the error happening:
> > http://sl4.dmclub.org/ee_error.png
> >
> > And in this folder are some shots of the error report:
> > http://sl4.dmclub.org/wads/ee-error/
> >
> > The error seems to occur within the function I_SDLUpdateSound
> > (this is the closest symbol to the crash address found in the map file
> > generated by Visual C++). That function can be found in this file:
> >
> > http://eternity.mancubus.net/svn/trunk/eternity/source/i_sound.c
> >
> > I cannot make any inroads against this problem, since the crash is
> > only occurring for this particular user. Literally thousands of man 
>hours
> > of play testing have gone into the game without this error ever
> > occuring elsewhere, so I'm hesitant to blame my own code. If
> > anyone has any clues as to what could cause this, I'd be highly
> > appreciative.
>
>I'm wondering if he's got an onboard audio chip that can only ever do
>48000Hz for a sample rate...SDL would probably be trying to upsample,
>incorrectly, from 44100Hz.
>
>SDL 1.2 is buggy when resampling from rates that aren't multiples...so
>it could do 24000Hz to 48000Hz or 48000Hz to 96000Hz, but 44100 to 48000
>would probably cause an internal buffer in SDL to overflow.
>
>Add a call to Mix_QuerySpec() in there after the Mix_OpenAudio() call
>and see what it reports. Consider failing to initialize the game's audio
>subsystem if Mix_QuerySpec() doesn't report a frequency that
>snd_samplerate is a multiple of (or vice versa)...at least, until
>someone fixes that bug in SDL. Hell, SDL should probably just fail in
>this case, in the meantime, too.
>
>Based on a first look at your code, that would be my best guess. Most
>audio hardware can do 41000Hz, but I've seen motherboard chips that can
>only do 48000, and you might have just stumbled upon one for the first 
>time.
>
>--ryan.
>
>
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