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add a generic function to decode banding structure for coupling, spectral

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extension, or enhanced coupling

Originally committed as revision 15811 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2008-11-13 03:18:07 +00:00
parent 6c6f927289
commit 0c5d750df9
1 changed files with 67 additions and 17 deletions
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84
libavcodec/ac3dec.c
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@ -710,6 +710,68 @@ static void ac3_upmix_delay(AC3DecodeContext *s)
}
}
/**
* Decode band structure for coupling, spectral extension, or enhanced coupling.
* @param[in] gbc bit reader context
* @param[in] blk block number
* @param[in] eac3 flag to indicate E-AC-3
* @param[in] ecpl flag to indicate enhanced coupling
* @param[in] start_subband subband number for start of range
* @param[in] end_subband subband number for end of range
* @param[in] default_band_struct default band structure table
* @param[out] band_struct decoded band structure
* @param[out] num_subbands number of subbands (optionally NULL)
* @param[out] num_bands number of bands (optionally NULL)
* @param[out] band_sizes array containing the number of bins in each band (optionally NULL)
*/
static void decode_band_structure(GetBitContext *gbc, int blk, int eac3,
int ecpl, int start_subband, int end_subband,
const uint8_t *default_band_struct,
uint8_t *band_struct, int *num_subbands,
int *num_bands, int *band_sizes)
{
int subbnd, bnd, n_subbands, n_bands, bnd_sz[22];
n_subbands = end_subband - start_subband;
/* decode band structure from bitstream or use default */
if (!eac3 || get_bits1(gbc)) {
for (subbnd = 0; subbnd < n_subbands - 1; subbnd++) {
band_struct[subbnd] = get_bits1(gbc);
}
} else if (!blk) {
memcpy(band_struct,
&default_band_struct[start_subband+1],
n_subbands-1);
}
band_struct[n_subbands-1] = 0;
/* calculate number of bands and band sizes based on band structure.
note that the first 4 subbands in enhanced coupling span only 6 bins
instead of 12. */
if (num_bands || band_sizes ) {
n_bands = n_subbands;
bnd_sz[0] = ecpl ? 6 : 12;
for (bnd = 0, subbnd = 1; subbnd < n_subbands; subbnd++) {
int subbnd_size = (ecpl && subbnd < 4) ? 6 : 12;
if (band_struct[subbnd-1]) {
n_bands--;
bnd_sz[bnd] += subbnd_size;
} else {
bnd_sz[++bnd] = subbnd_size;
}
}
}
/* set optional output params */
if (num_subbands)
*num_subbands = n_subbands;
if (num_bands)
*num_bands = n_bands;
if (band_sizes)
memcpy(band_sizes, bnd_sz, sizeof(int)*n_bands);
}
/**
* Decode a single audio block from the AC-3 bitstream.
*/
@ -812,23 +874,11 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
s->start_freq[CPL_CH] = cpl_start_subband * 12 + 37;
s->end_freq[CPL_CH] = cpl_end_subband * 12 + 37;
/* coupling band structure */
s->num_cpl_bands = s->num_cpl_subbands;
if (!s->eac3 || get_bits1(gbc)) {
for (bnd = 0; bnd < s->num_cpl_subbands - 1; bnd++) {
s->cpl_band_struct[bnd] = get_bits1(gbc);
}
} else if (!blk) {
memcpy(s->cpl_band_struct,
&ff_eac3_default_cpl_band_struct[cpl_start_subband+1],
s->num_cpl_subbands-1);
}
s->cpl_band_struct[s->num_cpl_subbands-1] = 0;
/* calculate number of coupling bands based on band structure */
for (bnd = 0; bnd < s->num_cpl_subbands-1; bnd++) {
s->num_cpl_bands -= s->cpl_band_struct[bnd];
}
decode_band_structure(gbc, blk, s->eac3, 0,
cpl_start_subband, cpl_end_subband,
ff_eac3_default_cpl_band_struct,
s->cpl_band_struct, &s->num_cpl_subbands,
&s->num_cpl_bands, NULL);
} else {
/* coupling not in use */
for (ch = 1; ch <= fbw_channels; ch++) {