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From e275318cecee53cf8ce13e4ab41df91c8c7fdcd4 Mon Sep 17 00:00:00 2001
From: John Stebbins <stebbins@jetheaddev.com>
Date: Mon, 13 Jan 2014 17:04:30 +0000
Subject: [PATCH] ac3dec: Allow asymmetric application of DRC when drc_scale >
1
Amplification of quiet sounds is enhanced.
Inspired by gbooker's A52Decoder.
---
libavcodec/ac3dec.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index 87638e7..0416dbc 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -772,8 +772,13 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
i = !s->channel_mode;
do {
if (get_bits1(gbc)) {
- s->dynamic_range[i] = powf(dynamic_range_tab[get_bits(gbc, 8)],
- s->drc_scale);
+ /* Allow asymmetric application of DRC when drc_scale > 1.
+ Amplification of quiet sounds is enhanced */
+ float range = dynamic_range_tab[get_bits(gbc, 8)];
+ if (range > 1.0 || s->drc_scale <= 1.0)
+ s->dynamic_range[i] = powf(range, s->drc_scale);
+ else
+ s->dynamic_range[i] = range;
} else if (blk == 0) {
s->dynamic_range[i] = 1.0f;
}
@@ -1487,7 +1492,7 @@ static av_cold int ac3_decode_end(AVCodecContext *avctx)
#define OFFSET(x) offsetof(AC3DecodeContext, x)
#define PAR (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)
static const AVOption options[] = {
- { "drc_scale", "percentage of dynamic range compression to apply", OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {.dbl = 1.0}, 0.0, 1.0, PAR },
+ { "drc_scale", "percentage of dynamic range compression to apply", OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {.dbl = 1.0}, 0.0, 6.0, PAR },
{ NULL},
};
--
1.8.3.4 (Apple Git-47)
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