From 1408352ada60d5a174b48d547114bb086812fcdb Mon Sep 17 00:00:00 2001
From: Justin Ruggles <justin.ruggles@gmail.com>
Date: Thu, 20 Dec 2007 00:55:08 +0000
Subject: [PATCH] Add option for user to scale the amount of dynamic range
 compression which is applied by the audio decoder, and use that option in the
 AC3 decoder.

Originally committed as revision 11280 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 libavcodec/ac3dec.c  | 3 ++-
 libavcodec/avcodec.h | 8 ++++++++
 libavcodec/utils.c   | 1 +
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index 468723f285..c06edc46e5 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -792,7 +792,8 @@ static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
     i = !(ctx->channel_mode);
     do {
         if(get_bits1(gb)) {
-            ctx->dynamic_range[i] = dynamic_range_tab[get_bits(gb, 8)];
+            ctx->dynamic_range[i] = ((dynamic_range_tab[get_bits(gb, 8)]-1.0) *
+                                    ctx->avctx->drc_scale)+1.0;
         } else if(blk == 0) {
             ctx->dynamic_range[i] = 1.0f;
         }
diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 88d600c50f..a32f961403 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -2154,6 +2154,14 @@ typedef struct AVCodecContext {
      * - decoding: Set by user.
      */
     int request_channels;
+
+    /**
+     * Percentage of dynamic range compression to be applied by the decoder.
+     * The default value is 1.0, corresponding to full compression.
+     * - encoding: unused
+     * - decoding: Set by user.
+     */
+    float drc_scale;
 } AVCodecContext;
 
 /**
diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index 290814dcca..3b5ef7a773 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -761,6 +761,7 @@ static const AVOption options[]={
 {"drop_frame_timecode", NULL, 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_DROP_FRAME_TIMECODE, INT_MIN, INT_MAX, V|E, "flags2"},
 {"non_linear_q", "use non linear quantizer", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_NON_LINEAR_QUANT, INT_MIN, INT_MAX, V|E, "flags2"},
 {"request_channels", "set desired number of audio channels", OFFSET(request_channels), FF_OPT_TYPE_INT, DEFAULT, 0, INT_MAX, A|D},
+{"drc_scale", "percentage of dynamic range compression to apply", OFFSET(drc_scale), FF_OPT_TYPE_FLOAT, 1.0, 0.0, 1.0, A|D},
 {NULL},
 };