support mp3 decoding over libavcodec

platform/common/mp3_libavcodec.c

@@ -0,0 +1,117 @@
+/*
+ * Some mp3 related code for Sega/Mega CD.
+ * Uses Libav/FFmpeg libavcodec
+ * (C) notaz, 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 <libavcodec/avcodec.h>
+
+#include <pico/pico_int.h>
+#include "../libpicofe/lprintf.h"
+#include "mp3.h"
+
+static AVCodecContext *ctx;
+
+int mp3dec_decode(FILE *f, int *file_pos, int file_len)
+{
+	unsigned char input_buf[2 * 1024];
+	int frame_size;
+	AVPacket avpkt;
+	int bytes_in;
+	int bytes_out;
+	int offset;
+	int len;
+
+	av_init_packet(&avpkt);
+
+	do
+	{
+		if (*file_pos >= file_len)
+			return 1; // EOF, nothing to do
+
+		fseek(f, *file_pos, SEEK_SET);
+		bytes_in = fread(input_buf, 1, sizeof(input_buf), f);
+
+		offset = mp3_find_sync_word(input_buf, bytes_in);
+		if (offset < 0) {
+			lprintf("find_sync_word (%i/%i) err %i\n",
+				*file_pos, file_len, offset);
+			*file_pos = file_len;
+			return 1; // EOF
+		}
+
+		// to avoid being flooded with "incorrect frame size" errors,
+		// we must calculate and pass exact frame size - lame
+		frame_size = mpeg1_l3_bitrates[input_buf[offset + 2] >> 4];
+		frame_size = frame_size * 144000 / 44100;
+		frame_size += (input_buf[offset + 2] >> 1) & 1;
+
+		if (offset > 0 && bytes_in - offset < frame_size) {
+			// underflow
+			*file_pos += offset;
+			continue;
+		}
+
+		avpkt.data = input_buf + offset;
+		avpkt.size = frame_size;
+		bytes_out = sizeof(cdda_out_buffer);
+
+		len = avcodec_decode_audio3(ctx, cdda_out_buffer,
+			&bytes_out, &avpkt);
+		if (len <= 0) {
+			lprintf("mp3 decode err (%i/%i) %i\n",
+				*file_pos, file_len, len);
+
+			// attempt to skip the offending frame..
+			*file_pos += offset + 1;
+			continue;
+		}
+
+		*file_pos += offset + len;
+	}
+	while (0);
+
+	return 0;
+}
+
+int mp3dec_start(void)
+{
+	AVCodec *codec;
+	int ret;
+
+	if (ctx != NULL)
+		return 0;
+
+	// init decoder
+
+	//avcodec_init();
+	avcodec_register_all();
+
+	// AV_CODEC_ID_MP3 ?
+	codec = avcodec_find_decoder(CODEC_ID_MP3);
+	if (codec == NULL) {
+		lprintf("mp3dec: codec missing\n");
+		return -1;
+	}
+
+	ctx = avcodec_alloc_context();
+	if (ctx == NULL) {
+		lprintf("mp3dec: avcodec_alloc_context failed\n");
+		return -1;
+	}
+
+	ret = avcodec_open(ctx, codec);
+	if (ret < 0) {
+		lprintf("mp3dec: avcodec_open failed: %d\n", ret);
+		av_free(ctx);
+		ctx = NULL;
+		return -1;
+	}
+
+	return 0;
+}