loosen dependencies over mpegaudiodec

Originally committed as revision 9080 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegaudio_parser.c

@@ -22,6 +22,7 @@
 
 #include "parser.h"
 #include "mpegaudio.h"
+#include "mpegaudiodecheader.h"
 
 
 typedef struct MpegAudioParseContext {
@@ -41,6 +42,43 @@ typedef struct MpegAudioParseContext {
 #define SAME_HEADER_MASK \
    (0xffe00000 | (3 << 17) | (3 << 10) | (3 << 19))
 
+/* useful helper to get mpeg audio stream infos. Return -1 if error in
+   header, otherwise the coded frame size in bytes */
+int mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate)
+{
+    MPADecodeContext s1, *s = &s1;
+    s1.avctx = avctx;
+
+    if (ff_mpa_check_header(head) != 0)
+        return -1;
+
+    if (decode_header(s, head) != 0) {
+        return -1;
+    }
+
+    switch(s->layer) {
+    case 1:
+        avctx->frame_size = 384;
+        break;
+    case 2:
+        avctx->frame_size = 1152;
+        break;
+    default:
+    case 3:
+        if (s->lsf)
+            avctx->frame_size = 576;
+        else
+            avctx->frame_size = 1152;
+        break;
+    }
+
+    *sample_rate = s->sample_rate;
+    avctx->channels = s->nb_channels;
+    avctx->bit_rate = s->bit_rate;
+    avctx->sub_id = s->layer;
+    return s->frame_size;
+}
+
 static int mpegaudio_parse_init(AVCodecParserContext *s1)
 {
     MpegAudioParseContext *s = s1->priv_data;