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use cutoff frequency to adjust bandwidth in ac3 encoder

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Originally committed as revision 11338 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2007-12-28 06:13:55 +00:00
parent 08ac1e783e
commit 02c164c148
2 changed files with 15 additions and 5 deletions
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18
libavcodec/ac3enc.c
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@ -632,6 +632,7 @@ static int AC3_encode_init(AVCodecContext *avctx)
AC3EncodeContext *s = avctx->priv_data;
int i, j, ch;
float alpha;
int bw_code;
static const uint8_t channel_mode_defs[6] = {
0x01, /* C */
0x02, /* L R */
@ -683,12 +684,21 @@ static int AC3_encode_init(AVCodecContext *avctx)
s->frame_size = s->frame_size_min;
/* bit allocation init */
for(ch=0;ch<s->nb_channels;ch++) {
/* bandwidth for each channel */
if(avctx->cutoff) {
/* calculate bandwidth based on user-specified cutoff frequency */
int cutoff = av_clip(avctx->cutoff, 1, s->sample_rate >> 1);
int fbw_coeffs = cutoff * 512 / s->sample_rate;
bw_code = av_clip((fbw_coeffs - 73) / 3, 0, 60);
} else {
/* use default bandwidth setting */
/* XXX: should compute the bandwidth according to the frame
size, so that we avoid anoying high freq artefacts */
s->chbwcod[ch] = 50; /* sample bandwidth as mpeg audio layer 2 table 0 */
s->nb_coefs[ch] = ((s->chbwcod[ch] + 12) * 3) + 37;
bw_code = 50;
}
for(ch=0;ch<s->nb_channels;ch++) {
/* bandwidth for each channel */
s->chbwcod[ch] = bw_code;
s->nb_coefs[ch] = bw_code * 3 + 73;
}
if (s->lfe) {
s->nb_coefs[s->lfe_channel] = 7; /* fixed */

2
libavcodec/avcodec.h
View File

@ -2072,7 +2072,7 @@ typedef struct AVCodecContext {
int directpred;
/**
* Audio cutoff bandwidth (0 means "automatic"), currently used only by FAAC.
* Audio cutoff bandwidth (0 means "automatic")
* - encoding: Set by user.
* - decoding: unused
*/