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Bug 1014

Summary: SDL_ConvertAudio crashes
Product: SDL Reporter: Mārtiņš Možeiko <mm.5p4mbox>
Component: audioAssignee: Ryan C. Gordon <icculus>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: critical    
Priority: P2    
Version: HG 2.0   
Hardware: x86   
OS: Windows 7   
Attachments: Reproducing crash
patch for sdlgenaudiocvt.pl

Description Mārtiņš Možeiko 2010-07-01 02:09:21 UTC 
When converting AUDIO_S16, 16kHz, 1 channel audio to AUDIO_S16, 44.1kHz, 2 channel  crash occurs in SDL_ConvertAudio function. Crash happens somewhere in SDL_Upsample_S16LSB_2c function.

I'm using MSVC2008 to build SDL from hg.

Code to reproduce crash is attached. Same code with SDL-1.2.14 runs fine and prints out: "Converted from 10 to 40"
Comment 1 Mārtiņš Možeiko 2010-07-01 02:10:29 UTC 
Created attachment 513 [details]
Reproducing crash
Comment 2 Mark.Howson 2010-12-15 07:41:49 UTC 
Created attachment 549 [details]
patch for sdlgenaudiocvt.pl
Comment 3 Mark.Howson 2010-12-15 07:45:25 UTC 
Reproducible here under Windows and Linux. Looking at the code for SDL_Upsample_S16LSB_2c:

const int dstsize = (int) (((double)cvt->len_cvt) * cvt->rate_incr);
Sint16 *dst = ((Sint16 *) (cvt->buf + dstsize)) - 2;
const Sint16 *target = ((const Sint16 *) cvt->buf) - 2;
while (dst > target) {
   dst[1] = ((Sint16) SDL_SwapLE16(sample1));
   dst[0] = ((Sint16) SDL_SwapLE16(sample0));
   dst -= 2;
...

if dstsize is odd (and therefore dst), it'll write to target[1] which is one byte before the allocated buf.

The attached patch to sdlgenaudiocvt.pl changes dst > target to dst >= target, and removes the - $channels for the upsample case. The patch is not fully tested, but seems to work here.
Comment 4 Sam Lantinga 2012-01-08 14:11:28 UTC 
Looks good, thanks!
http://hg.libsdl.org/SDL/rev/ba275696ab7a