(e)ac3: clip surround mix level indexes.

Values 0-2 are reserved, 3 (-1.5dB) should be used instead.

libavcodec/ac3dec.c

@@ -237,9 +237,9 @@ static int ac3_parse_header(AC3DecodeContext *s)
         if (get_bits1(gbc)) {
             s->preferred_downmix       = get_bits(gbc, 2);
             s->center_mix_level_ltrt   = get_bits(gbc, 3);
-            s->surround_mix_level_ltrt = get_bits(gbc, 3);
+            s->surround_mix_level_ltrt = av_clip(get_bits(gbc, 3), 3, 7);
             s->center_mix_level        = get_bits(gbc, 3);
-            s->surround_mix_level      = get_bits(gbc, 3);
+            s->surround_mix_level      = av_clip(get_bits(gbc, 3), 3, 7);
         }
         if (get_bits1(gbc)) {
             s->dolby_surround_ex_mode = get_bits(gbc, 2);

libavcodec/eac3dec.c

@@ -353,8 +353,8 @@ int ff_eac3_parse_header(AC3DecodeContext *s)
             }
             if (s->channel_mode & 4) {
                 /* if a surround channel exists */
-                s->surround_mix_level_ltrt = get_bits(gbc, 3);
-                s->surround_mix_level = get_bits(gbc, 3);
+                s->surround_mix_level_ltrt = av_clip(get_bits(gbc, 3), 3, 7);
+                s->surround_mix_level = av_clip(get_bits(gbc, 3), 3, 7);
             }
         }