support mp3 decoding over libavcodec

platform/common/mp3.c

@@ -1,12 +1,26 @@
 /*
  * PicoDrive
- * (C) notaz, 2010
+ * (C) notaz, 2010,2013
  *
  * This work is licensed under the terms of MAME license.
  * See COPYING file in the top-level directory.
  */
+#include <stdio.h>
+#include <string.h>
+
+#include <pico/pico_int.h>
+#include <pico/sound/mix.h>
 #include "mp3.h"
 
+static FILE *mp3_current_file;
+static int mp3_file_len, mp3_file_pos;
+static int cdda_out_pos;
+static int decoder_active;
+
+unsigned short mpeg1_l3_bitrates[16] = {
+	0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320
+};
+
 int mp3_find_sync_word(const unsigned char *buf, int size)
 {
 	const unsigned char *p, *pe;
@@ -34,3 +48,152 @@ int mp3_find_sync_word(const unsigned char *buf, int size)
 	return -1;
 }
 
+static int try_get_bitrate(unsigned char *buf, int buf_size)
+{
+	int offs1, offs = 0;
+	int ret;
+
+	while (1)
+	{
+		offs1 = mp3_find_sync_word(buf + offs, buf_size - offs);
+		if (offs1 < 0)
+			return -2;
+		offs += offs1;
+		if (buf_size - offs < 4)
+			return -3;
+
+		// printf("trying header %08x\n", *(int *)(buf + offs));
+
+		ret = mpeg1_l3_bitrates[buf[offs + 2] >> 4];
+		if (ret > 0)
+			return ret;
+	}
+
+	return -2;
+}
+
+int mp3_get_bitrate(void *f_, int len)
+{
+	unsigned char buf[2048];
+	FILE *f = f_;
+	int retval = -1;
+	int ret;
+
+	memset(buf, 0, sizeof(buf));
+
+	fseek(f, 0, SEEK_SET);
+	ret = fread(buf, 1, sizeof(buf), f);
+	if (ret != sizeof(buf))
+		goto out;
+
+	ret = try_get_bitrate(buf, sizeof(buf));
+	if (ret <= 0) {
+		// try to read somewhere around the middle
+		fseek(f, len / 2, SEEK_SET);
+		fread(buf, 1, sizeof(buf), f);
+		ret = try_get_bitrate(buf, sizeof(buf));
+	}
+	if (ret > 0)
+		retval = ret;
+
+	//printf("bitrate: %i\n", retval);
+
+out:
+	fseek(f, 0, SEEK_SET);
+	return retval;
+}
+
+void mp3_start_play(void *f_, int pos)
+{
+	unsigned char buf[2048];
+	FILE *f = f_;
+	int ret;
+
+	mp3_file_len = mp3_file_pos = 0;
+	mp3_current_file = NULL;
+	cdda_out_pos = 0;
+	decoder_active = 0;
+
+	if (!(PicoOpt & POPT_EN_MCD_CDDA) || f == NULL) // cdda disabled or no file?
+		return;
+
+	ret = mp3dec_start();
+	if (ret != 0)
+		return;
+
+	decoder_active = 1;
+
+	mp3_current_file = f;
+	fseek(f, 0, SEEK_END);
+	mp3_file_len = ftell(f);
+
+	// search for first sync word, skipping stuff like ID3 tags
+	while (mp3_file_pos < 128*1024) {
+		int offs, bytes;
+
+		fseek(f, mp3_file_pos, SEEK_SET);
+		bytes = fread(buf, 1, sizeof(buf), f);
+		if (bytes < 4)
+			break;
+		offs = mp3_find_sync_word(buf, bytes);
+		if (offs >= 0) {
+			mp3_file_pos += offs;
+			break;
+		}
+		mp3_file_pos += bytes - 3;
+	}
+
+	// seek..
+	if (pos) {
+		unsigned long long pos64 = mp3_file_len - mp3_file_pos;
+		pos64 *= pos;
+		mp3_file_pos += pos64 >> 10;
+	}
+
+	mp3dec_decode(mp3_current_file, &mp3_file_pos, mp3_file_len);
+}
+
+void mp3_update(int *buffer, int length, int stereo)
+{
+	int length_mp3, shr = 0;
+	void (*mix_samples)(int *dest_buf, short *mp3_buf, int count) = mix_16h_to_32;
+
+	if (mp3_current_file == NULL || mp3_file_pos >= mp3_file_len)
+		return; /* no file / EOF */
+
+	if (!decoder_active)
+		return;
+
+	length_mp3 = length;
+	if (PsndRate <= 11025 + 100) {
+		mix_samples = mix_16h_to_32_s2;
+		length_mp3 <<= 2; shr = 2;
+	}
+	else if (PsndRate <= 22050 + 100) {
+		mix_samples = mix_16h_to_32_s1;
+		length_mp3 <<= 1; shr = 1;
+	}
+
+	if (1152 - cdda_out_pos >= length_mp3) {
+		mix_samples(buffer, cdda_out_buffer + cdda_out_pos * 2,
+			length * 2);
+
+		cdda_out_pos += length_mp3;
+	} else {
+		int ret, left = 1152 - cdda_out_pos;
+
+		mix_samples(buffer, cdda_out_buffer + cdda_out_pos * 2,
+			(left >> shr) * 2);
+
+		ret = mp3dec_decode(mp3_current_file, &mp3_file_pos,
+			mp3_file_len);
+		if (ret == 0) {
+			cdda_out_pos = length_mp3 - left;
+			mix_samples(buffer + (left >> shr) * 2,
+				cdda_out_buffer,
+				(cdda_out_pos >> shr) * 2);
+		} else
+			cdda_out_pos = 0;
+	}
+}
+