libfdk-aacdec: Allow explicitly disabling the DRC reference level option

Previously, it was always left in the automatic mode, if the option
was set to the only special (negative) value. Now there's two separate
special values for this option, -1 for automatic (metadata based)
and -2 for explicitly disabled.

Signed-off-by: Martin Storsjö <martin@martin.st>

1 files changed, 8 insertions, 2 deletions

diff --git a/libavcodec/libfdk-aacdec.c b/libavcodec/libfdk-aacdec.c
index ec7f236ce7..1a86dffe4b 100644
--- a/libavcodec/libfdk-aacdec.c
+++ b/libavcodec/libfdk-aacdec.c
@@ -76,8 +76,8 @@ static const AVOption fdk_aac_dec_options[] = {
                      OFFSET(drc_boost),      AV_OPT_TYPE_INT,   { .i64 = -1 }, -1, 127, AD, NULL    },
     { "drc_cut",   "Dynamic Range Control: attenuation factor, where [0] is none and [127] is max compression",
                      OFFSET(drc_cut),        AV_OPT_TYPE_INT,   { .i64 = -1 }, -1, 127, AD, NULL    },
-    { "drc_level", "Dynamic Range Control: reference level, quantized to 0.25dB steps where [0] is 0dB and [127] is -31.75dB",
-                     OFFSET(drc_level),      AV_OPT_TYPE_INT,   { .i64 = -1},  -1, 127, AD, NULL    },
+    { "drc_level", "Dynamic Range Control: reference level, quantized to 0.25dB steps where [0] is 0dB and [127] is -31.75dB, -1 for auto, and -2 for disabled",
+                     OFFSET(drc_level),      AV_OPT_TYPE_INT,   { .i64 = -1},  -2, 127, AD, NULL    },
     { "drc_heavy", "Dynamic Range Control: heavy compression, where [1] is on (RF mode) and [0] is off",
                      OFFSET(drc_heavy),      AV_OPT_TYPE_INT,   { .i64 = -1},  -1, 1,   AD, NULL    },
 #if FDKDEC_VER_AT_LEAST(2, 5) // 2.5.10
@@ -299,6 +299,12 @@ static av_cold int fdk_aac_decode_init(AVCodecContext *avctx)
     }
 
     if (s->drc_level != -1) {
+        // This option defaults to -1, i.e. not calling
+        // aacDecoder_SetParam(AAC_DRC_REFERENCE_LEVEL) at all, which defaults
+        // to the level from DRC metadata, if available. The user can set
+        // -drc_level -2, which calls aacDecoder_SetParam(
+        // AAC_DRC_REFERENCE_LEVEL) with a negative value, which then
+        // explicitly disables the feature.
         if (aacDecoder_SetParam(s->handle, AAC_DRC_REFERENCE_LEVEL, s->drc_level) != AAC_DEC_OK) {
             av_log(avctx, AV_LOG_ERROR, "Unable to set DRC reference level in the decoder\n");
             return AVERROR_UNKNOWN;