adx: move header decoding to ADX common code

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;
+}