Encode signed 16 bit 16 kHz PCM to FLAC file

simple_flac_encoder.c

#include "FLAC/stream_encoder.h"

#define CHUNKSIZE 512

FLAC__StreamEncoderWriteStatus callback
    (const FLAC__StreamEncoder *encoder
    ,const FLAC__byte buffer[]
    ,size_t bytes
    ,unsigned samples
    ,unsigned current_frame
    ,void *client_data)
{
    /* write to file */
    FILE *output_file = (FILE*) client_data;
    fprintf(stdout, "writing %d bytes\n", samples);
    fwrite((void*)buffer, 1, bytes, output_file);

    return FLAC__STREAM_ENCODER_WRITE_STATUS_OK;
}

int main(int argc, char *argv[])
{
    FLAC__int16 buffer[CHUNKSIZE];
    FLAC__int32 flac_buffer[CHUNKSIZE];
    FLAC__int32 const *flac_buffers[] = {flac_buffer};
    FLAC__StreamEncoder *p_enc = FLAC__stream_encoder_new();

    /* open output file */
    FILE *output_file = fopen("output.flac", "w+b");
    if(!output_file)
    {
        fprintf(stderr, "Error opening output file\n");
        return -1;
    }

    /* initialize the encoder and stream callback function */
    FLAC__stream_encoder_set_channels(p_enc, 1);
    FLAC__stream_encoder_set_bits_per_sample(p_enc, 16);
    FLAC__stream_encoder_set_sample_rate(p_enc, 16000);
    FLAC__stream_encoder_init_stream(p_enc, callback, NULL, NULL, NULL, output_file);

    /* process entire file */
    FILE *input_file = fopen("vice.pcm", "r+b");
    if(!input_file)
    {
        fprintf(stderr, "Error opening input file\n");
        return -1;
    }

    /* process entire pcm file */
    for(;;)
    {
        /* try to read a full chunk */
        const size_t num_read = fread(buffer, sizeof(FLAC__int16), CHUNKSIZE, input_file);

        /* check for EOF */
        if(num_read == 0)
        {
            break;
        }

        /* cast FLAC__int16 to a buffer of FLAC__int32 */
        for(int i = 0; i < num_read; ++i)
        {
            flac_buffer[i] = (FLAC__int32)buffer[i];
        }

        /* process the buffer */
        fprintf(stdout, "processing %zu (16-bit/2-byte) samples\n", num_read);
        FLAC__stream_encoder_process(p_enc, flac_buffers, CHUNKSIZE);
    }

    /* finish and clean up */
    FLAC__stream_encoder_finish(p_enc);
    FLAC__stream_encoder_delete(p_enc);
    fclose(output_file);
    fclose(input_file);

    return 0;
}