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ffmpeg/libavcodec/dca_xll.h
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Vincent Herbst 1191609d38 avcodec/dca_xll: decode the height channels of the DTS:X standard presentation 
A DTS:X stream in the standard presentation is DTS-HD Master Audio with a 7.1
bed and an extension at the end of every XLL frame, behind the syncword the
decoder already recognises (DCA_SYNCWORD_XLL_X). The extension is a 22-byte
header followed by a regular XLL channel set: four channels, every one coded
in full (no residual against the core), no speaker mask, its own NAVI table
with the frame's segment geometry, then a two-byte trailer. Its channels are
the front and rear height pairs, and the encoder folds each of them into the
bed speaker below it (L, R, Lsr, Rsr) at -3 dB, gain code 23170/32768, so the
7.1 bed plays them on players that ignore the extension.

The decoder now parses that channel set with the existing channel set code,
outputs 7.1.4 (TFL, TFR, TBL, TBR), and removes the fold from the bed at
output resolution. A "downmix" request for 7.1 keeps the bed as coded, heights
folded in, which is what the decoder output before; the requests for 5.1 and
stereo skip the extension as well, so their output is unchanged. Streams
without the extension are not affected. A frame whose extension does not
decode keeps the 7.1.4 layout with silent heights and the bed as coded, and
the frame still ends where it did before. The alternate presentations, which
carry objects behind DCA_SYNCWORD_XLL_X_IMAX, are not touched.

The format facts (header size, channel order, the fold) come from the public
analysis in harletty-bridge's dca crate and kristofferR's SpatialAudioBridge;
this is an implementation on FFmpeg's own XLL code, not a translation.

Signed-off-by: Vincent Herbst <superuser404@tuta.com>
2026-10-26 13:11:19 +00:00

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/*
* Copyright (C) 2016 foo86
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef AVCODEC_DCA_XLL_H
#define AVCODEC_DCA_XLL_H
#include "libavutil/mem_internal.h"
#include "avcodec.h"
#include "get_bits.h"
#include "dca.h"
#include "dcadsp.h"
#include "dca_exss.h"
#define DCA_XLL_CHSETS_MAX 3
#define DCA_XLL_CHANNELS_MAX 8
#define DCA_XLL_BANDS_MAX 2
#define DCA_XLL_ADAPT_PRED_ORDER_MAX 16
#define DCA_XLL_DECI_HISTORY_MAX 8
#define DCA_XLL_DMIX_SCALES_MAX ((DCA_XLL_CHSETS_MAX - 1) * DCA_XLL_CHANNELS_MAX)
#define DCA_XLL_DMIX_COEFFS_MAX (DCA_XLL_DMIX_SCALES_MAX * DCA_XLL_CHANNELS_MAX)
#define DCA_XLL_PBR_BUFFER_MAX (240 << 10)
#define DCA_XLL_SAMPLE_BUFFERS_MAX 3
typedef struct DCAXllBand {
int decor_enabled; ///< Pairwise channel decorrelation flag
int orig_order[DCA_XLL_CHANNELS_MAX]; ///< Original channel order
int decor_coeff[DCA_XLL_CHANNELS_MAX / 2]; ///< Pairwise channel coefficients
int adapt_pred_order[DCA_XLL_CHANNELS_MAX]; ///< Adaptive predictor order
int highest_pred_order; ///< Highest adaptive predictor order
int fixed_pred_order[DCA_XLL_CHANNELS_MAX]; ///< Fixed predictor order
int adapt_refl_coeff[DCA_XLL_CHANNELS_MAX][DCA_XLL_ADAPT_PRED_ORDER_MAX]; ///< Adaptive predictor reflection coefficients
int dmix_embedded; ///< Downmix performed by encoder in frequency band
int lsb_section_size; ///< Size of LSB section in any segment
int nscalablelsbs[DCA_XLL_CHANNELS_MAX]; ///< Number of bits to represent the samples in LSB part
int bit_width_adjust[DCA_XLL_CHANNELS_MAX]; ///< Number of bits discarded by authoring
int32_t *msb_sample_buffer[DCA_XLL_CHANNELS_MAX]; ///< MSB sample buffer pointers
int32_t *lsb_sample_buffer[DCA_XLL_CHANNELS_MAX]; ///< LSB sample buffer pointers or NULL
} DCAXllBand;
typedef struct DCAXllChSet {
// Channel set header
int nchannels; ///< Number of channels in the channel set (N)
int residual_encode; ///< Residual encoding mask (0 - residual, 1 - full channel)
int pcm_bit_res; ///< PCM bit resolution (variable)
int storage_bit_res; ///< Storage bit resolution (16 or 24)
int freq; ///< Original sampling frequency (max. 96000 Hz)
int primary_chset; ///< Primary channel set flag
int dmix_coeffs_present; ///< Downmix coefficients present in stream
int dmix_embedded; ///< Downmix already performed by encoder
int dmix_type; ///< Primary channel set downmix type
int hier_chset; ///< Whether the channel set is part of a hierarchy
int hier_ofs; ///< Number of preceding channels in a hierarchy (M)
int dmix_coeff[DCA_XLL_DMIX_COEFFS_MAX]; ///< Downmixing coefficients
int dmix_scale[DCA_XLL_DMIX_SCALES_MAX]; ///< Downmixing scales
int dmix_scale_inv[DCA_XLL_DMIX_SCALES_MAX]; ///< Inverse downmixing scales
int ch_mask; ///< Channel mask for set
int ch_remap[DCA_XLL_CHANNELS_MAX]; ///< Channel to speaker map
int nfreqbands; ///< Number of frequency bands (1 or 2)
int nabits; ///< Number of bits to read bit allocation coding parameter
DCAXllBand bands[DCA_XLL_BANDS_MAX]; ///< Frequency bands
// Frequency band coding parameters
int seg_common; ///< Segment type
int rice_code_flag[DCA_XLL_CHANNELS_MAX]; ///< Rice coding flag
int bitalloc_hybrid_linear[DCA_XLL_CHANNELS_MAX]; ///< Binary code length for isolated samples
int bitalloc_part_a[DCA_XLL_CHANNELS_MAX]; ///< Coding parameter for part A of segment
int bitalloc_part_b[DCA_XLL_CHANNELS_MAX]; ///< Coding parameter for part B of segment
int nsamples_part_a[DCA_XLL_CHANNELS_MAX]; ///< Number of samples in part A of segment
// Decimator history
DECLARE_ALIGNED(32, int32_t, deci_history)[DCA_XLL_CHANNELS_MAX][DCA_XLL_DECI_HISTORY_MAX]; ///< Decimator history for frequency band 1
// Sample buffers
unsigned int sample_size[DCA_XLL_SAMPLE_BUFFERS_MAX];
int32_t *sample_buffer[DCA_XLL_SAMPLE_BUFFERS_MAX];
} DCAXllChSet;
typedef struct DCAXllDecoder {
AVCodecContext *avctx;
GetBitContext gb;
int frame_size; ///< Number of bytes in a lossless frame
int nchsets; ///< Number of channels sets per frame
int nframesegs; ///< Number of segments per frame
int nsegsamples_log2; ///< log2(nsegsamples)
int nsegsamples; ///< Samples in segment per one frequency band
int nframesamples_log2; ///< log2(nframesamples)
int nframesamples; ///< Samples in frame per one frequency band
int seg_size_nbits; ///< Number of bits used to read segment size
int band_crc_present; ///< Presence of CRC16 within each frequency band
int scalable_lsbs; ///< MSB/LSB split flag
int ch_mask_nbits; ///< Number of bits used to read channel mask
int fixed_lsb_width; ///< Fixed LSB width
DCAXllChSet chset[DCA_XLL_CHSETS_MAX]; ///< Channel sets
int *navi; ///< NAVI table
unsigned int navi_size;
int nfreqbands; ///< Highest number of frequency bands
int nchannels; ///< Total number of channels in a hierarchy
int nreschsets; ///< Number of channel sets that have residual encoded channels
int nactivechsets; ///< Number of active channel sets to decode
int hd_stream_id; ///< Previous DTS-HD stream ID for detecting changes
uint8_t *pbr_buffer; ///< Peak bit rate (PBR) smoothing buffer
int pbr_length; ///< Length in bytes of data currently buffered
int pbr_delay; ///< Delay in frames before decoding buffered data
DCADSPContext *dcadsp;
int x_syncword_present; ///< Syncword for extension data at end of frame (DTS:X) is present
int x_imax_syncword_present; ///< Syncword for extension data at end of frame (DTS:X IMAX) is present
DCAXllChSet x_chset; ///< Height channel set of the DTS:X standard presentation
int x_heights; ///< Output carries the four heights (sticky once seen)
int x_heights_decoded; ///< Heights of the current frame decoded
int32_t *x_silence; ///< Silent heights for a frame whose heights did not decode
unsigned int x_silence_size;
int output_mask;
int32_t *output_samples[DCA_SPEAKER_COUNT];
} DCAXllDecoder;
int ff_dca_xll_parse(DCAXllDecoder *s, const uint8_t *data, DCAExssAsset *asset);
int ff_dca_xll_filter_frame(DCAXllDecoder *s, AVFrame *frame);
av_cold void ff_dca_xll_flush(DCAXllDecoder *s);
av_cold void ff_dca_xll_close(DCAXllDecoder *s);
#endif
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