/*----------------------------------------------------------------------------
.MP3 file dumper
Chris Giese	<ChrisGiese@SisAndHappy.com>
http://SisAndHappy.com/ChrisGiese

This code is public domain (no copyright).
You can do whatever you want with it.

24 Aug 2018: first release
----------------------------------------------------------------------------*/
#include <stdio.h>
/****************************************************************************/
int main(int arg_c, char *arg_v[])
{
	static const char *mpeg_ver[2] =
	{
		"MPEG-2", "MPEG-1"
	};
	static const unsigned freq_table[2][4] =
	{
		{
			22050u, 24000u, 16000u, 0	/* MPEG-2 */
		}, {
			44100u, 48000u, 32000u, 0	/* MPEG-1 */
		}
	};
	static const unsigned short bitrate_table[2][4][16] =
	{
		{/* MPEG-2 */
			{0,32,48,56,64,80,96,112,128,144,160,176,192,224,256,0},
			{0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0},
			{0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0},
			{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}
		},{/* MPEG-1 */
			{0,32,64,96,128,160,192,224,256,288,320,352,384,416,448,0},
			{0,32,48,56,64,80,96,112,128,160,192,224,256,320,384,0},
			{0,32,40,48,56,64,80,96,112,128,160,192,224,256,320,0},
			{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}
		}
	};
	static const char *mode_table[4] =
	{
		"stereo", "joint stereo", "dual-channel", "mono"
	};
	static char buf[4];
/**/
	unsigned mpeg_id, layer, no_crc, bitrate_index, freq_index;
	unsigned has_padding, mode/*, mode_ext*/, bitrate, freq, bytes;
	unsigned long pos;
	FILE *in;
	int i;

	if(arg_c != 2)
	{
		printf("Dumps .MP3 files\n");
		return 1;
	}
	if((in = fopen(arg_v[1], "rb")) == NULL)
	{
		printf("Error: can't open input file %s\n", arg_v[1]);
		return 2;
	}
	buf[0] = 0xFF;
	while(1)
	{
/* eleven '1' bits = sync at start of an MP3 frame */
		do
		{
			do
			{
				if((i = fgetc(in)) == EOF)
					goto DONE;
			} while(i != 0xFF);
			if((i = fgetc(in)) == EOF)
				goto DONE;
		} while((i & 0xE0) != 0xE0);
/* it _still_ might not be an MP3 header -- validate below */
		buf[1] = i;
		pos = ftell(in) - 2;
/* read remaining two bytes of header */
		if(fread(&buf[2], 1, 2, in) != 2)
		{
			printf("Error: unexpected end of input file %s\n",
				arg_v[1]);
			return 2;
		}
/* ID: 1=MPEG-1, 0=MPEG-2 */
		mpeg_id		= (buf[1] >> 3) & 1;
/* layer: 0=?, 1=layer III, 2=layer II, 3=layer I */
		layer		= (buf[1] >> 1) & 3;
		no_crc		= (buf[1] & 1);

		bitrate_index	= (buf[2] >> 4) & 15;
		freq_index	= (buf[2] >> 2) & 3;
		has_padding	= (buf[2] >> 1) & 1;

		mode		= (buf[3] >> 6) & 3;
//		mode_ext	= mode ? 0 : (buf[3] >> 4) & 3;
/* validate */
		if(layer == 0 || bitrate_index == 15 || freq_index == 3)
		{
			fseek(in, -3, SEEK_CUR);
			continue;
		}
/* variable frame size ("free format") */
		if(bitrate_index == 0)
		{
			fseek(in, -3, SEEK_CUR);
			continue;
		}
		bitrate = bitrate_table[mpeg_id][3 - layer]
			[bitrate_index];
		freq = freq_table[mpeg_id][freq_index];
		printf("%7lu ID=%u (%s), layer=%u, no_crc=%u, bitrate_"
			"index=%2u (bitrate=%3u), freq_index=%u (freq=%u), "
			"has_padding=%u, mode=%u (%s)\n", pos, mpeg_id,
			mpeg_ver[mpeg_id], 4 - layer, no_crc, bitrate_index,
			bitrate, freq_index, freq, has_padding, mode,
			mode_table[mode]);
		bytes = (unsigned)((mpeg_id ? 144000L : 72000L)
			* bitrate / freq);
		if(has_padding)
			bytes++;
		if(!no_crc)
			bytes += 2;
		fseek(in, pos + bytes, SEEK_SET);
	}
DONE:
	fclose(in);
	return 0;
}