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ac3dec: Allow asymmetric application of DRC when drc_scale > 1 

Amplification of quiet sounds is enhanced.
Inspired by gbooker's A52Decoder.
This commit is contained in:
John Stebbins 2014-01-13 17:04:30 +00:00 committed by Tim Walker
parent d67cfdeb53
commit 23d461fe87
1 changed files with 8 additions and 3 deletions
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11
libavcodec/ac3dec.c
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@ -778,8 +778,13 @@ 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;
}
@ -1493,7 +1498,7 @@ 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},
};