avcodec: Add avpriv_mpa_decode_header2()

The difference to avpriv_mpa_decode_header() is that it doesnt need or modify the context
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegaudiodecheader.c

@@ -108,7 +108,7 @@ int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
     return 0;
 }
 
-int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
+int avpriv_mpa_decode_header2(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
 {
     MPADecodeHeader s1, *s = &s1;
 
@@ -121,16 +121,16 @@ int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_r
 
     switch(s->layer) {
     case 1:
-        avctx->codec_id = AV_CODEC_ID_MP1;
+        *codec_id = AV_CODEC_ID_MP1;
         *frame_size = 384;
         break;
     case 2:
-        avctx->codec_id = AV_CODEC_ID_MP2;
+        *codec_id = AV_CODEC_ID_MP2;
         *frame_size = 1152;
         break;
     default:
     case 3:
-        avctx->codec_id = AV_CODEC_ID_MP3;
+        *codec_id = AV_CODEC_ID_MP3;
         if (s->lsf)
             *frame_size = 576;
         else
@@ -143,3 +143,8 @@ int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_r
     *bit_rate = s->bit_rate;
     return s->frame_size;
 }
+
+int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
+{
+    return avpriv_mpa_decode_header2(head, sample_rate, channels, frame_size, bit_rate, &avctx->codec_id);
+}

libavcodec/mpegaudiodecheader.h

@@ -56,6 +56,8 @@ int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header);
    header, otherwise the coded frame size in bytes */
 int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bitrate);
 
+int avpriv_mpa_decode_header2(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bitrate, enum AVCodecID *codec_id);
+
 /* fast header check for resync */
 static inline int ff_mpa_check_header(uint32_t header){
     /* header */

libavcodec/version.h

@@ -29,7 +29,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVCODEC_VERSION_MAJOR 55
-#define LIBAVCODEC_VERSION_MINOR  50
+#define LIBAVCODEC_VERSION_MINOR  51
 #define LIBAVCODEC_VERSION_MICRO 100
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \