How to find the right RAW format

问题

I have this code

SNDFILE *sf;
SF_INFO info;
int num_channels;
int num, num_items;
int *buf;
int f,sr,c;
int i,j;
FILE *out;

/* Open the WAV file. */
info.format     = (SF_FORMAT_RAW | SF_FORMAT_PCM_16);  
info.samplerate = 44100;
info.channels = 2;  

sf = sf_open("test.raw",SFM_READ,&info);

if (sf == NULL)
    {
    printf("Failed to open the file. ( %d )\n",sf_perror(sf));
    exit(-1);
    }
/* Print some of the info, and figure out how much data to read. */
f = info.frames;
sr = info.samplerate;
c = info.channels;
num_items = f*c;
/* Allocate space for the data to be read, then read it. */
buf = (int *) malloc(num_items*sizeof(int));
num = sf_read_int(sf,buf,num_items);
sf_close(sf);
printf("Read %d items\n",num);
/* Write the data to filedata.out. */
out = fopen("test.txt","w");  
int links;
int rechts;
for (i = 0; i < num; i += c)
{
  for (j = 0; j < c; ++j)
      fprintf(out,"%d ",buf[i+j]);
  fprintf(out,"\n");
}  
fclose(out);

It's purpose is to read "test.raw", convert it to an array and write this into "test.txt". "test.raw" is a raw pcm created by

...    
static const pa_sample_spec ss = 
{
    .format = PA_SAMPLE_S16LE,
    .rate = 44100,
    .channels = 2
};
pa_simple *s = NULL;
int ret = 1;
int error;
s = pa_simple_new(NULL, 
        "rec", 
        PA_STREAM_RECORD, 
        "bluez_source.00_00_00_00_00_00", 
        "rec", 
        &ss, 
        NULL, 
        NULL, 
        &error)  
...

from the pulseaudio audio recording sample(download).

Thing is, I get something like

219676672 -131072 
219676672 327680 
219611136 655360 
219217920 327680 
218955776 -131072 
219152384 -393216 
218693632 -720896

in test.txt. I added headers, to get

SAMPLES:    365568
BITSPERSAMPLE:  16
CHANNELS:   2
SAMPLERATE: 44100
NORMALIZED: FALSE
219676672 -131072 
219676672 327680 
219611136 655360 
219217920 327680 
218955776 -131072 
219152384 -393216 
218693632 -720896

and imported into adobe audition as ascii file. I use 44100, 16 bit and stereo there aswell as the intel(also tried the motorola).

Each time I only get "bars" ie periods of constant volume. When reading "test.raw" in audition i see the data as it should be using the intel property.

What do I need to tweak for this to work?

回答1:

By looking at your data, it seems that you have a confusion between 16-bit and 32-bit signed integer data. Your .raw data is 16-bit and is probably okay, but your .txt data has numbers like 219676672, -131072 which is clearly out of 16-bit data range (minimum is -32768, maximum is 32767).

What you are describing as Each time I only get "bars" i.e. periods of constant volume, is called saturation: You are trying to display numbers above the limits so the values are replaced by the limit. Audition detects your data is 32-bit so it will display it correctly.

How to fix it?

I think your int is 32-bit, so you should not store read data to an int, but a short or the 16-bit equivalent.

short *buf;

. . .

/* Allocate space for the data to be read, then read it. */
buf = (short *) malloc(num_items*sizeof(short));
num = sf_read_short(sf,buf,num_items);

来源：https://stackoverflow.com/questions/17547110/how-to-find-the-right-raw-format

标签

pulseaudio

libsndfile