avcodec/aacdec: print a log message when treating mono HE-AAC as stereo

Since this behavior is intentional, use the VERBOSE level instead of WARNING as
it's nothing the user should worry about.

Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/aac.h

@@ -366,6 +366,7 @@ struct AACContext {
     int warned_960_sbr;
     unsigned warned_71_wide;
     int warned_gain_control;
+    int warned_he_aac_mono;
 
     /* aacdec functions pointers */
     void (*imdct_and_windowing)(AACContext *ac, SingleChannelElement *sce);

libavcodec/aacdec_template.c

@@ -2584,6 +2584,10 @@ static int decode_extension_payload(AACContext *ac, GetBitContext *gb, int cnt,
             ac->avctx->profile = FF_PROFILE_AAC_HE;
         }
         res = AAC_RENAME(ff_decode_sbr_extension)(ac, &che->sbr, gb, crc_flag, cnt, elem_type);
+        if (ac->oc[1].m4ac.ps == 1 && !ac->warned_he_aac_mono) {
+            av_log(ac->avctx, AV_LOG_VERBOSE, "Treating HE-AAC mono as stereo.\n");
+            ac->warned_he_aac_mono = 1;
+        }
         break;
     case EXT_DYNAMIC_RANGE:
         res = decode_dynamic_range(&ac->che_drc, gb);

libavcodec/aacsbr_template.c

@@ -955,6 +955,8 @@ static void read_sbr_extension(AACContext *ac, SpectralBandReplication *sbr,
         } else {
             *num_bits_left -= ff_ps_read_data(ac->avctx, gb, &sbr->ps.common, *num_bits_left);
             ac->avctx->profile = FF_PROFILE_AAC_HE_V2;
+            // ensure the warning is not printed if PS extension is present
+            ac->warned_he_aac_mono = 1;
         }
         break;
     default: