audio-tool/wav_chan_splitter.c

/*
 * wav_chan_splitter.c
 *
 * Utility for splitting a multichannel wav file to multiple mono wav files.
 */

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

#include "wav_chan_splitter.h"

#define MAX_FILENAME_LEN 256
#define MAX_CHANNELS 8
#define MAX_BYTES 4 // Up to 32-bit samples

/* Reuse tinyplay/tinycap code for header parsing */
static int parse_header (char * filename, wav_header_t * 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(wav_header_t), 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;
}

/* Create mono header based on multichannel header  */
static int create_new_header (wav_header_t * wav_header_out, wav_header_t * wav_header) {
	if (!wav_header_out || !wav_header) {
		fprintf(stderr, "Invalid argument for %s\n", __func__);
		return 1;
	}
	memcpy(wav_header_out, wav_header, sizeof(wav_header_t));
	wav_header_out->num_channels = 1;
	wav_header_out->byte_rate = (wav_header->byte_rate)/(wav_header->num_channels);
	wav_header_out->block_align = (wav_header->block_align)/(wav_header->num_channels);
	wav_header_out->data_sz = (wav_header->data_sz)/(wav_header->num_channels);
	/* Tinycap doesn't set riff_sz field, fill it up for the split files */
	/* Definition: size of the rest of header (36 bytes) + datachunk size */
	wav_header_out->riff_sz = wav_header_out->data_sz + 36;
	return 0;
}

static int split (char *filename, const wav_header_t * wav_header, const wav_header_t * wav_header_out) {
	char outname[MAX_FILENAME_LEN];
	uint8_t i = 0;
	char *extension_pos;
	FILE *fp;                   /* input file pointer  */
	FILE *fplist[MAX_CHANNELS]; /* output file pointers  */
	uint8_t data[MAX_CHANNELS*MAX_BYTES];
        size_t num_bytes_per_sample;

	fp = fopen(filename, "rb");
	/* Jump to data block  */
	fseek(fp, sizeof(wav_header_t), 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;
	}

	printf("splitting...\n");

	/* Create files <filename_[01 - N].wav> and copy headers */
	for (i = 0; i < wav_header->num_channels; i++) {
		snprintf(extension_pos, sizeof(outname) - (extension_pos - outname), "_%02d.wav", i + 1);
		fplist[i] = fopen(outname, "wb");
		fwrite(wav_header_out, sizeof(wav_header_t), 1, fplist[i]);
	}

        num_bytes_per_sample = wav_header_out->bits_per_sample >> 3;

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

	for (i = 0; i < wav_header->num_channels; i++) {
		fclose(fplist[i]);
	}
	fclose(fp);
	return 0;
}

int split_main (int argc, char* argv[]) {
	char *filename;
	wav_header_t wav_header, wav_header_out;

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

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

	printf("filename: %s\nformat: %d\nnum_channels: %d\nsample_rate: %d\nbyte_rate: %d\nblock_align: %d\nbits_per_sample: %d\n\n",
		filename, wav_header.audio_format, wav_header.num_channels, wav_header.sample_rate,
		wav_header.byte_rate, wav_header.block_align, wav_header.bits_per_sample);

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

	if (wav_header.num_channels <= 1) {
		fprintf(stderr, "Error: audio channel is already mono or invalid\n");
		return 1;
	}

	if (create_new_header(&wav_header_out, &wav_header))
		return 1;

	if(split(filename, &wav_header, &wav_header_out))
		return 1;

	printf("Done!\n");
	return 0;
}