Segmentation fault in samplerate conversion function - c

Question

playmp3() using libmpg123
if (isPaused==0 && mpg123_read(mh, buffer, buffer_size, &done) == MPG123_OK)
{
char * resBuffer=&buffer[0]; //22100=0,5s
buffer = resample(resBuffer,22100,22100);
if((ao_play(dev, (char*)buffer, done)==0)){
return 1;
}
resample() Using avcodec from ffmpeg
#define LENGTH_MS 500 // how many milliseconds of speech to store
#define RATE 44100 // the sampling rate (input)
#define FORMAT PA_SAMPLE_S16NE // sample size: 8 or 16 bits
#define CHANNELS 2 // 1 = mono 2 = stereo
struct AVResampleContext* audio_cntx = 0;
char * resample(char in_buffer[(LENGTH_MS*RATE*16*CHANNELS)/8000],int out_rate,int nsamples)
{
char out_buffer[ sizeof( in_buffer ) * 4];
audio_cntx = av_resample_init( out_rate, //out rate
RATE, //in rate
16, //filter length
10, //phase count
0, //linear FIR filter
1.0 ); //cutoff frequency
assert( audio_cntx && "Failed to create resampling context!");
int samples_consumed;
int samples_output = av_resample( audio_cntx, //resample context
(short*)out_buffer, //buffout
(short*)in_buffer, //buffin
&samples_consumed, //&consumed
nsamples, //nb_samples
sizeof(out_buffer)/2,//lenout
0);//is_last
assert( samples_output > 0 && "Error calling av_resample()!" );
av_resample_close( audio_cntx );
//*resample = malloc(sizeof(out_buffer));
return &out_buffer[0];
}
When i run this code i get 3393 Segmentation fault (core dump created). Why?
For example, the use of pointers is correct?
and 22100 are the samples that are contained in 0.5 seconds of the song?

Answer 1

You have two issues that I can see right off the bat. These are noob questions, but everyone does this at least once, so don't worry!
Check that sizeof( in_buffer ) is giving you the size of the buffer you expect ((LENGTH_MS*RATE*16*CHANNELS)/8000) or the size of the pointer(which would be 2, 4 or 8 depending on your system.) Using sizeof on an array on the stack gives you its total size, because there is no pointer only a buffer. Sizeof an array on the parameter list gives you the size of the pointer even if you use [] on the param list, because there only is a pointer.
Also, returning a stack based buffer is undefined (i.e. will crash), since the stack gets reused on the next function call:
return &out_buffer[0];
Don't do that. Pass in the out buffer already allocated by the caller.