diff --git a/libavcodec/adx.c b/libavcodec/adx.c
index bc3e8825cacfad123e7c096bf6dea27fe24f9640..9f03e930be7e6ddd488f43f76e87f30b87495359 100644
--- a/libavcodec/adx.c
+++ b/libavcodec/adx.c
@@ -18,6 +18,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "libavutil/intreadwrite.h"
 #include "libavutil/mathematics.h"
 #include "adx.h"
 
@@ -32,3 +33,49 @@ void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
     coeff[0] = lrintf(c * 2.0  * (1 << bits));
     coeff[1] = lrintf(-(c * c) * (1 << bits));
 }
+
+int ff_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf, int bufsize,
+                         int *header_size, int *coeff)
+{
+    int offset, cutoff;
+
+    if (bufsize < 24)
+        return AVERROR_INVALIDDATA;
+
+    if (AV_RB16(buf) != 0x8000)
+        return AVERROR_INVALIDDATA;
+    offset = AV_RB16(buf + 2) + 4;
+
+    /* if copyright string is within the provided data, validate it */
+    if (bufsize >= offset && memcmp(buf + offset - 6, "(c)CRI", 6))
+        return AVERROR_INVALIDDATA;
+
+    /* check for encoding=3 block_size=18, sample_size=4 */
+    if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {
+        av_log_ask_for_sample(avctx, "unsupported ADX format\n");
+        return AVERROR_PATCHWELCOME;
+    }
+
+    /* channels */
+    avctx->channels = buf[7];
+    if (avctx->channels > 2)
+        return AVERROR_INVALIDDATA;
+
+    /* sample rate */
+    avctx->sample_rate = AV_RB32(buf + 8);
+    if (avctx->sample_rate < 1 ||
+        avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
+        return AVERROR_INVALIDDATA;
+
+    /* bit rate */
+    avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
+
+    /* LPC coefficients */
+    if (coeff) {
+        cutoff = AV_RB16(buf + 16);
+        ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, coeff);
+    }
+
+    *header_size = offset;
+    return 0;
+}
diff --git a/libavcodec/adx.h b/libavcodec/adx.h
index cd8c45bf6df2815021860c3f9f2833c3209fc40a..f68a3cb79325dd05904d4db298880c0761dfdaac 100644
--- a/libavcodec/adx.h
+++ b/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 */
diff --git a/libavcodec/adxdec.c b/libavcodec/adxdec.c
index e9226b2bd9ae52dc0d2069b5bc22baf9b475e308..0b0eac262ca9dff256c4c2637d37685d6267afaa 100644
--- a/libavcodec/adxdec.c
+++ b/libavcodec/adxdec.c
@@ -33,9 +33,6 @@
  * adx2wav & wav2adx http://www.geocities.co.jp/Playtown/2004/
  */
 
-#define BLOCK_SIZE      18
-#define BLOCK_SAMPLES   32
-
 static av_cold int adx_decode_init(AVCodecContext *avctx)
 {
     avctx->sample_fmt = AV_SAMPLE_FMT_S16;
@@ -72,45 +69,18 @@ static void adx_decode(ADXContext *c, int16_t *out, const uint8_t *in, int ch)
     prev->s2 = s2;
 }
 
-/**
- * Decode stream header.
- *
- * @param avctx   codec context
- * @param buf     packet data
- * @param bufsize packet size
- * @return data offset or negative error code if header is invalid
- */
 static int adx_decode_header(AVCodecContext *avctx, const uint8_t *buf,
                              int bufsize)
 {
     ADXContext *c = avctx->priv_data;
-    int offset, cutoff;
-
-    if (AV_RB16(buf) != 0x8000)
-        return AVERROR_INVALIDDATA;
-    offset = AV_RB16(buf + 2) + 4;
-    if (bufsize < offset || memcmp(buf + offset - 6, "(c)CRI", 6))
-        return AVERROR_INVALIDDATA;
-
-    /* check for encoding=3 block_size=18, sample_size=4 */
-    if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {
-        av_log_ask_for_sample(avctx, "unsupported ADX format\n");
-        return AVERROR_PATCHWELCOME;
-    }
-
-    c->channels = avctx->channels = buf[7];
-    if (avctx->channels > 2)
-        return AVERROR_INVALIDDATA;
-    avctx->sample_rate = AV_RB32(buf + 8);
-    if (avctx->sample_rate < 1 ||
-        avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
-        return AVERROR_INVALIDDATA;
-    avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
+    int ret, header_size;
 
-    cutoff = AV_RB16(buf + 16);
-    ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, c->coeff);
+    if ((ret = ff_adx_decode_header(avctx, buf, bufsize, &header_size,
+                                    c->coeff)) < 0)
+        return ret;
 
-    return offset;
+    c->channels = avctx->channels;
+    return header_size;
 }
 
 static int adx_decode_frame(AVCodecContext *avctx, void *data, int *data_size,