adpcm: fix IMA SMJPEG decoding

Signed-off-by: Janne Grunau <janne-libav@jannau.net>

libavcodec/adpcm.c

@@ -1001,11 +1001,15 @@ static int adpcm_decode_frame(AVCodecContext *avctx, void *data,
         break;
     case CODEC_ID_ADPCM_IMA_AMV:
     case CODEC_ID_ADPCM_IMA_SMJPEG:
-        c->status[0].predictor = (int16_t)bytestream_get_le16(&src);
+        if (avctx->codec->id == CODEC_ID_ADPCM_IMA_AMV) {
+            c->status[0].predictor = sign_extend(bytestream_get_le16(&src), 16);
             c->status[0].step_index = bytestream_get_le16(&src);
-
-        if (avctx->codec->id == CODEC_ID_ADPCM_IMA_AMV)
-            src+=4;
+            src += 4;
+        } else {
+            c->status[0].predictor = sign_extend(bytestream_get_be16(&src), 16);
+            c->status[0].step_index = bytestream_get_byte(&src);
+            src += 1;
+        }
 
         for (n = nb_samples >> (1 - st); n > 0; n--, src++) {
             char hi, lo;