adx: move header decoding to ADX common code

libavcodec/adx.h

@@ -31,6 +31,10 @@
 #ifndef AVCODEC_ADX_H
 #define AVCODEC_ADX_H
 
+#include <stdint.h>
+
+#include "avcodec.h"
+
 typedef struct {
     int s1,s2;
 } ADXChannelState;
@@ -47,6 +51,9 @@ typedef struct {
 
 #define COEFF_BITS  12
 
+#define BLOCK_SIZE      18
+#define BLOCK_SAMPLES   32
+
 /**
  * Calculate LPC coefficients based on cutoff frequency and sample rate.
  *
@@ -57,4 +64,18 @@ typedef struct {
  */
 void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff);
 
+/**
+ * Decode ADX stream header.
+ * Sets avctx->channels and avctx->sample_rate.
+ *
+ * @param      avctx        codec context
+ * @param      buf          header data
+ * @param      bufsize      data size, should be at least 24 bytes
+ * @param[out] header_size  size of ADX header
+ * @param[out] coeff        2 LPC coefficients, can be NULL
+ * @return data offset or negative error code if header is invalid
+ */
+int ff_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf, int bufsize,
+                         int *header_size, int *coeff);
+
 #endif /* AVCODEC_ADX_H */