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Code Issues Releases Activity

downmix before the IMDCT if no block switching is used

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Originally committed as revision 11228 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2007-12-16 04:25:50 +00:00
parent 15c57ced2f
commit b40211ff67
1 changed files with 34 additions and 13 deletions
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47
libavcodec/ac3dec.c
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@ -750,27 +750,28 @@ static inline void do_imdct(AC3DecodeContext *ctx)
/**
* Downmix the output to mono or stereo.
*/
static void ac3_downmix(float samples[AC3_MAX_CHANNELS][256], int fbw_channels,
int output_mode, float coef[AC3_MAX_CHANNELS][2])
static void ac3_downmix(float samples[][256], int fbw_channels,
int output_mode, float coef[AC3_MAX_CHANNELS][2],
int ch_offset)
{
int i, j;
float v0, v1, s0, s1;
for(i=0; i<256; i++) {
v0 = v1 = s0 = s1 = 0.0f;
for(j=0; j<fbw_channels; j++) {
v0 += samples[j][i] * coef[j][0];
v1 += samples[j][i] * coef[j][1];
s0 += coef[j][0];
s1 += coef[j][1];
for(j=ch_offset; j<fbw_channels+ch_offset; j++) {
v0 += samples[j][i] * coef[j-ch_offset][0];
v1 += samples[j][i] * coef[j-ch_offset][1];
s0 += coef[j-ch_offset][0];
s1 += coef[j-ch_offset][1];
}
v0 /= s0;
v1 /= s1;
if(output_mode == AC3_CHMODE_MONO) {
samples[0][i] = (v0 + v1) * LEVEL_MINUS_3DB;
samples[ch_offset][i] = (v0 + v1) * LEVEL_MINUS_3DB;
} else if(output_mode == AC3_CHMODE_STEREO) {
samples[0][i] = v0;
samples[1][i] = v1;
samples[ch_offset][i] = v0;
samples[ch_offset+1][i] = v1;
}
}
}
@ -785,12 +786,16 @@ static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
int i, bnd, seg, ch;
GetBitContext *gb = &ctx->gb;
uint8_t bit_alloc_stages[AC3_MAX_CHANNELS];
int any_block_switching = 0;
int num_channels_bak, fbw_channels_bak;
memset(bit_alloc_stages, 0, AC3_MAX_CHANNELS);
/* block switch flags */
for (ch = 1; ch <= fbw_channels; ch++)
for (ch = 1; ch <= fbw_channels; ch++) {
ctx->block_switch[ch] = get_bits1(gb);
any_block_switching |= ctx->block_switch[ch];
}
/* dithering flags */
ctx->dither_all = 1;
@ -1062,13 +1067,26 @@ static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
}
}
/* if no block switching is used, downmixing can be done before IMDCT */
num_channels_bak = ctx->channels;
fbw_channels_bak = ctx->fbw_channels;
if(!any_block_switching) {
if(ctx->channels != ctx->out_channels && !((ctx->output_mode & AC3_OUTPUT_LFEON) &&
ctx->fbw_channels == ctx->out_channels)) {
ac3_downmix(ctx->transform_coeffs, ctx->fbw_channels,
ctx->output_mode, ctx->downmix_coeffs, 1);
ctx->channels = ctx->out_channels;
ctx->fbw_channels = ctx->channels - (ctx->output_mode & AC3_OUTPUT_LFEON);
}
}
do_imdct(ctx);
/* downmix output if needed */
/* downmix output now if it wasn't done before IMDCT */
if(ctx->channels != ctx->out_channels && !((ctx->output_mode & AC3_OUTPUT_LFEON) &&
ctx->fbw_channels == ctx->out_channels)) {
ac3_downmix(ctx->output, ctx->fbw_channels, ctx->output_mode,
ctx->downmix_coeffs);
ctx->downmix_coeffs, 0);
}
/* convert float to 16-bit integer */
@ -1079,6 +1097,9 @@ static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
ctx->dsp.float_to_int16(ctx->int_output[ch], ctx->output[ch], 256);
}
ctx->channels = num_channels_bak;
ctx->fbw_channels = fbw_channels_bak;
return 0;
}