diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index 5ebee1908d..fbcfdb0ce9 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -207,13 +207,6 @@ static av_cold int ac3_decode_init(AVCodecContext *avctx)
     }
     s->downmixed = 1;
 
-    /* allocate context input buffer */
-    if (avctx->error_recognition >= FF_ER_CAREFUL) {
-        s->input_buffer = av_mallocz(AC3_FRAME_BUFFER_SIZE + FF_INPUT_BUFFER_PADDING_SIZE);
-        if (!s->input_buffer)
-            return AVERROR(ENOMEM);
-    }
-
     avctx->sample_fmt = AV_SAMPLE_FMT_S16;
     return 0;
 }
@@ -1312,16 +1305,27 @@ static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size,
     int blk, ch, err;
     const uint8_t *channel_map;
     const float *output[AC3_MAX_CHANNELS];
+    // if it seems to be byte-swapped AC-3 (aka DNET)
+    int is_swapped = buf_size >= 2 && AV_RB16(buf) == 0x770B;
 
     /* initialize the GetBitContext with the start of valid AC-3 Frame */
-    if (s->input_buffer) {
+    if (is_swapped || avctx->error_recognition >= FF_ER_CAREFUL) {
+        /* allocate context input buffer */
+        if (!s->input_buffer)
+            s->input_buffer = av_mallocz(AC3_FRAME_BUFFER_SIZE + FF_INPUT_BUFFER_PADDING_SIZE);
+        if (!s->input_buffer)
+            return AVERROR(ENOMEM);
+
         /* copy input buffer to decoder context to avoid reading past the end
            of the buffer, which can be caused by a damaged input stream. */
+        if (is_swapped) {
+            int cnt = FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE) >> 1;
+            s->dsp.bswap16_buf(s->input_buffer, buf, cnt);
+        } else
         memcpy(s->input_buffer, buf, FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE));
-        init_get_bits(&s->gbc, s->input_buffer, buf_size * 8);
-    } else {
-        init_get_bits(&s->gbc, buf, buf_size * 8);
+        buf = s->input_buffer;
     }
+    init_get_bits(&s->gbc, buf, buf_size * 8);
 
     /* parse the syncinfo */
     *data_size = 0;