audio-tool/rms.c

/*
 * rms.c
 *
 * calculate RMS of a wav file per channel
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#include <inttypes.h>

#include "rms.h"

#define MAX_FILENAME_LEN 256
#define MAX_CHANNELS 8

#define ID_RIFF 0x46464952
#define ID_WAVE 0x45564157
#define ID_FMT  0x20746d66
#define ID_DATA 0x61746164

struct wav_header {
	uint32_t riff_id;
	uint32_t riff_sz;
	uint32_t riff_fmt;
	uint32_t fmt_id;
	uint32_t fmt_sz;
	uint16_t audio_format;
	uint16_t num_channels;
	uint32_t sample_rate;
	uint32_t byte_rate;
	uint16_t block_align;
	uint16_t bits_per_sample;
	uint32_t data_id;
	uint32_t data_sz;
};

/* Reuse tinyplay/tinycap code for header parsing */
static int parse_header (char * filename, struct wav_header * wav_header) {
	FILE* file;
	file = fopen(filename, "rb");
	if (!file) {
		fprintf(stderr, "Unable to open file '%s'\n", filename);
		return 1;
	}
	fread(wav_header, sizeof(struct wav_header), 1, file);
	if ((wav_header->riff_id != ID_RIFF) ||
			(wav_header->riff_fmt != ID_WAVE) ||
			(wav_header->data_id != ID_DATA)) {
		fprintf(stderr, "Error: '%s' is not a PCM Wav file\n", filename);
		fclose(file);
		return 1;
	}
	fclose(file);
	return 0;
}

static int rms (char *filename, const struct wav_header * wav_header) {
	char outname[MAX_FILENAME_LEN];
	uint8_t i = 0;
	char *extension_pos;
	FILE *fp;                   /* input file pointer  */
	uint16_t data[MAX_CHANNELS];
	uint64_t rms[MAX_CHANNELS];
	uint64_t num_samples = 0;

	fp = fopen(filename, "rb");
	/* Jump to data block  */
	fseek(fp, sizeof(struct wav_header), SEEK_SET);

	strncpy(outname, filename, sizeof(outname));
	/* Get extension index of filename */
	extension_pos = strrchr(outname, '.');
	/* Point to '\0' instead if no extension is found */
	if (!extension_pos)
		extension_pos = strrchr(outname, '\0');
	if (!extension_pos) {
		fprintf(stderr, "Filename is too long!\n");
		return 1;
	}

	/* Split data block */
	while(fread(data, wav_header->block_align, 1, fp) == 1) {
		num_samples++;
		for (i = 0; i < wav_header->num_channels; i++)
                        rms[i] += data[i]*data[i];
	}

	for (i = 0; i < wav_header->num_channels; i++) {
		printf("channel %d rms is %f\n",i, sqrt((float)rms[i])/num_samples);
	}
	fclose(fp);
	return 0;
}

int rms_main (int argc, char* argv[]) {
	char *filename;
	struct wav_header wav_header, wav_header_out;

	if (argc != 2) {
		fprintf(stderr, "Usage: audio-tool rms file.wav\n");
		return 1;
	}
	filename = argv[1];

	if (parse_header(filename, &wav_header))
		return 1;

	if (wav_header.num_channels > MAX_CHANNELS) {
		fprintf(stderr, "Error: only support %d or less channels\n", MAX_CHANNELS);
		return 1;
	}

	if(rms(filename, &wav_header))
		return 1;

	return 0;
}