[FFmpeg-cvslog] r12287 - trunk/libavcodec/ac3dec.c
jbr
subversion
Sat Mar 1 17:10:20 CET 2008
Author: jbr
Date: Sat Mar 1 17:10:19 2008
New Revision: 12287
Log:
use scale factor instead of sum for downmix level adjustment. avoids division
inside downmix loop. 7% faster 5.1-to-stereo downmixing.
Modified:
trunk/libavcodec/ac3dec.c
Modified: trunk/libavcodec/ac3dec.c
==============================================================================
--- trunk/libavcodec/ac3dec.c (original)
+++ trunk/libavcodec/ac3dec.c Sat Mar 1 17:10:19 2008
@@ -154,7 +154,7 @@ typedef struct {
int center_mix_level; ///< Center mix level index
int surround_mix_level; ///< Surround mix level index
float downmix_coeffs[AC3_MAX_CHANNELS][2]; ///< stereo downmix coefficients
- float downmix_coeff_sum[2]; ///< sum of downmix coeffs for each output channel
+ float downmix_coeff_adjust[2]; ///< adjustment needed for each output channel when downmixing
float dynamic_range[2]; ///< dynamic range
int cpl_coords[AC3_MAX_CHANNELS][18]; ///< coupling coordinates
int num_cpl_bands; ///< number of coupling bands
@@ -404,11 +404,14 @@ static void set_downmix_coeffs(AC3Decode
s->downmix_coeffs[nf][0] = s->downmix_coeffs[nf+1][1] = smix;
}
- s->downmix_coeff_sum[0] = s->downmix_coeff_sum[1] = 0.0f;
+ /* calculate adjustment needed for each channel to avoid clipping */
+ s->downmix_coeff_adjust[0] = s->downmix_coeff_adjust[1] = 0.0f;
for(i=0; i<s->fbw_channels; i++) {
- s->downmix_coeff_sum[0] += s->downmix_coeffs[i][0];
- s->downmix_coeff_sum[1] += s->downmix_coeffs[i][1];
+ s->downmix_coeff_adjust[0] += s->downmix_coeffs[i][0];
+ s->downmix_coeff_adjust[1] += s->downmix_coeffs[i][1];
}
+ s->downmix_coeff_adjust[0] = 1.0f / s->downmix_coeff_adjust[0];
+ s->downmix_coeff_adjust[1] = 1.0f / s->downmix_coeff_adjust[1];
}
/**
@@ -747,8 +750,8 @@ static void ac3_downmix(AC3DecodeContext
v0 += s->output[j][i] * s->downmix_coeffs[j][0];
v1 += s->output[j][i] * s->downmix_coeffs[j][1];
}
- v0 /= s->downmix_coeff_sum[0];
- v1 /= s->downmix_coeff_sum[1];
+ v0 *= s->downmix_coeff_adjust[0];
+ v1 *= s->downmix_coeff_adjust[1];
if(s->output_mode == AC3_CHMODE_MONO) {
s->output[0][i] = (v0 + v1) * LEVEL_MINUS_3DB;
} else if(s->output_mode == AC3_CHMODE_STEREO) {
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