wmapro decoder implementation Wmapro is an MDCT based codec comparable to wma standard or AAC. More...

#include "libavutil/float_dsp.h"
#include "libavutil/intfloat.h"
#include "libavutil/intreadwrite.h"
#include "avcodec.h"
#include "internal.h"
#include "get_bits.h"
#include "put_bits.h"
#include "wmaprodata.h"
#include "sinewin.h"
#include "wma.h"
#include "wma_common.h"

Data Structures
struct	WMAProChannelCtx
	frame specific decoder context for a single channel More...

struct	WMAProChannelGrp
	channel group for channel transformations More...

struct	WMAProDecodeCtx
	main decoder context More...

Macros
#define	WMAPRO_MAX_CHANNELS 8
	current decoder limitations

#define	MAX_SUBFRAMES 32
	max number of subframes per channel

#define	MAX_BANDS 29
	max number of scale factor bands

#define	MAX_FRAMESIZE 32768
	maximum compressed frame size

#define	WMAPRO_BLOCK_MIN_BITS 6
	log2 of min block size

#define	WMAPRO_BLOCK_MAX_BITS 13
	log2 of max block size

#define	WMAPRO_BLOCK_MIN_SIZE (1 << WMAPRO_BLOCK_MIN_BITS)
	minimum block size

#define	WMAPRO_BLOCK_MAX_SIZE (1 << WMAPRO_BLOCK_MAX_BITS)
	maximum block size

#define	WMAPRO_BLOCK_SIZES (WMAPRO_BLOCK_MAX_BITS - WMAPRO_BLOCK_MIN_BITS + 1)
	possible block sizes

#define	VLCBITS 9

#define	SCALEVLCBITS 8

#define	VEC4MAXDEPTH ((HUFF_VEC4_MAXBITS+VLCBITS-1)/VLCBITS)

#define	VEC2MAXDEPTH ((HUFF_VEC2_MAXBITS+VLCBITS-1)/VLCBITS)

#define	VEC1MAXDEPTH ((HUFF_VEC1_MAXBITS+VLCBITS-1)/VLCBITS)

#define	SCALEMAXDEPTH ((HUFF_SCALE_MAXBITS+SCALEVLCBITS-1)/SCALEVLCBITS)

#define	SCALERLMAXDEPTH ((HUFF_SCALE_RL_MAXBITS+VLCBITS-1)/VLCBITS)

#define	PRINT(a, b) av_log(s->avctx, AV_LOG_DEBUG, " %s = %d\n", a, b);

#define	PRINT_HEX(a, b) av_log(s->avctx, AV_LOG_DEBUG, " %s = %x\n", a, b);

Functions
static av_cold void	dump_context (WMAProDecodeCtx *s)
	helper function to print the most important members of the context

static av_cold int	decode_end (AVCodecContext *avctx)
	Uninitialize the decoder and free all resources.

static av_cold int	decode_init (AVCodecContext *avctx)
	Initialize the decoder.

static int	decode_subframe_length (WMAProDecodeCtx *s, int offset)
	Decode the subframe length.

static int	decode_tilehdr (WMAProDecodeCtx *s)
	Decode how the data in the frame is split into subframes.

static void	decode_decorrelation_matrix (WMAProDecodeCtx s, WMAProChannelGrp chgroup)
	Calculate a decorrelation matrix from the bitstream parameters.

static int	decode_channel_transform (WMAProDecodeCtx *s)
	Decode channel transformation parameters.

static int	decode_coeffs (WMAProDecodeCtx *s, int c)
	Extract the coefficients from the bitstream.

static int	decode_scale_factors (WMAProDecodeCtx *s)
	Extract scale factors from the bitstream.

static void	inverse_channel_transform (WMAProDecodeCtx *s)
	Reconstruct the individual channel data.

static void	wmapro_window (WMAProDecodeCtx *s)
	Apply sine window and reconstruct the output buffer.

static int	decode_subframe (WMAProDecodeCtx *s)
	Decode a single subframe (block).

static int	decode_frame (WMAProDecodeCtx s, AVFrame frame, int *got_frame_ptr)
	Decode one WMA frame.

static int	remaining_bits (WMAProDecodeCtx s, GetBitContext gb)
	Calculate remaining input buffer length.

static void	save_bits (WMAProDecodeCtx s, GetBitContext gb, int len, int append)
	Fill the bit reservoir with a (partial) frame.

static int	decode_packet (AVCodecContext avctx, void data, int got_frame_ptr, AVPacket avpkt)
	Decode a single WMA packet.

static void	flush (AVCodecContext *avctx)
	Clear decoder buffers (for seeking).

Variables
static VLC	sf_vlc
	scale factor DPCM vlc

static VLC	sf_rl_vlc
	scale factor run length vlc

static VLC	vec4_vlc
	4 coefficients per symbol

static VLC	vec2_vlc
	2 coefficients per symbol

static VLC	vec1_vlc
	1 coefficient per symbol

static VLC	coef_vlc [2]
	coefficient run length vlc codes

static float	sin64 [33]
	sine table for decorrelation

AVCodec	ff_wmapro_decoder
	wmapro decoder

Detailed Description

wmapro decoder implementation Wmapro is an MDCT based codec comparable to wma standard or AAC.

The decoding therefore consists of the following steps:

bitstream decoding
reconstruction of per-channel data
rescaling and inverse quantization
IMDCT
windowing and overlapp-add

The compressed wmapro bitstream is split into individual packets. Every such packet contains one or more wma frames. The compressed frames may have a variable length and frames may cross packet boundaries. Common to all wmapro frames is the number of samples that are stored in a frame. The number of samples and a few other decode flags are stored as extradata that has to be passed to the decoder.

The wmapro frames themselves are again split into a variable number of subframes. Every subframe contains the data for 2^N time domain samples where N varies between 7 and 12.

Example wmapro bitstream (in samples):

|| packet 0 || packet 1 || packet 2 packets

|| frame 0 || frame 1 || frame 2 || frames

|| | | || | | | || || subframes of channel 0

|| | | || | | | || || subframes of channel 1

The frame layouts for the individual channels of a wma frame does not need to be the same.

However, if the offsets and lengths of several subframes of a frame are the same, the subframes of the channels can be grouped. Every group may then use special coding techniques like M/S stereo coding to improve the compression ratio. These channel transformations do not need to be applied to a whole subframe. Instead, they can also work on individual scale factor bands (see below). The coefficients that carry the audio signal in the frequency domain are transmitted as huffman-coded vectors with 4, 2 and 1 elements. In addition to that, the encoder can switch to a runlevel coding scheme by transmitting subframe_length / 128 zero coefficients.

Before the audio signal can be converted to the time domain, the coefficients have to be rescaled and inverse quantized. A subframe is therefore split into several scale factor bands that get scaled individually. Scale factors are submitted for every frame but they might be shared between the subframes of a channel. Scale factors are initially DPCM-coded. Once scale factors are shared, the differences are transmitted as runlevel codes. Every subframe length and offset combination in the frame layout shares a common quantization factor that can be adjusted for every channel by a modifier. After the inverse quantization, the coefficients get processed by an IMDCT. The resulting values are then windowed with a sine window and the first half of the values are added to the second half of the output from the previous subframe in order to reconstruct the output samples.

Definition in file wmaprodec.c.

Macro Definition Documentation

#define WMAPRO_MAX_CHANNELS 8

current decoder limitations

max number of handled channels

Definition at line 102 of file wmaprodec.c.

Referenced by decode_decorrelation_matrix(), decode_init(), decode_tilehdr(), and inverse_channel_transform().

#define MAX_SUBFRAMES 32

max number of subframes per channel

Definition at line 103 of file wmaprodec.c.

Referenced by decode_init(), and decode_tilehdr().

#define MAX_BANDS 29

max number of scale factor bands

Definition at line 104 of file wmaprodec.c.

Referenced by decode_init().

#define MAX_FRAMESIZE 32768

maximum compressed frame size

Definition at line 105 of file wmaprodec.c.

Referenced by decode_init(), and save_bits().

#define WMAPRO_BLOCK_MIN_BITS 6

log2 of min block size

Definition at line 107 of file wmaprodec.c.

Referenced by decode_init(), decode_subframe(), and wmapro_window().

#define WMAPRO_BLOCK_MAX_BITS 13

log2 of max block size

Definition at line 108 of file wmaprodec.c.

Referenced by decode_init().

#define WMAPRO_BLOCK_MIN_SIZE (1 << WMAPRO_BLOCK_MIN_BITS)

minimum block size

Definition at line 109 of file wmaprodec.c.

Referenced by decode_init().

#define WMAPRO_BLOCK_MAX_SIZE (1 << WMAPRO_BLOCK_MAX_BITS)

maximum block size

Definition at line 110 of file wmaprodec.c.

Referenced by decode_subframe().

#define WMAPRO_BLOCK_SIZES (WMAPRO_BLOCK_MAX_BITS - WMAPRO_BLOCK_MIN_BITS + 1)

possible block sizes

Definition at line 111 of file wmaprodec.c.

Referenced by decode_end(), and decode_init().

#define VLCBITS 9

Definition at line 114 of file wmaprodec.c.

Referenced by decode_coeffs(), decode_init(), and decode_scale_factors().

#define SCALEVLCBITS 8

Definition at line 115 of file wmaprodec.c.

Referenced by decode_init(), and decode_scale_factors().

#define VEC4MAXDEPTH ((HUFF_VEC4_MAXBITS+VLCBITS-1)/VLCBITS)

Definition at line 116 of file wmaprodec.c.

Referenced by decode_coeffs().

#define VEC2MAXDEPTH ((HUFF_VEC2_MAXBITS+VLCBITS-1)/VLCBITS)

Definition at line 117 of file wmaprodec.c.

Referenced by decode_coeffs().

#define VEC1MAXDEPTH ((HUFF_VEC1_MAXBITS+VLCBITS-1)/VLCBITS)

Definition at line 118 of file wmaprodec.c.

Referenced by decode_coeffs().

#define SCALEMAXDEPTH ((HUFF_SCALE_MAXBITS+SCALEVLCBITS-1)/SCALEVLCBITS)

Definition at line 119 of file wmaprodec.c.

Referenced by decode_scale_factors().

#define SCALERLMAXDEPTH ((HUFF_SCALE_RL_MAXBITS+VLCBITS-1)/VLCBITS)

Definition at line 120 of file wmaprodec.c.

Referenced by decode_scale_factors().

#define PRINT	(	a,
		b
	)	av_log(s->avctx, AV_LOG_DEBUG, " %s = %d\n", a, b);

Referenced by dump_context(), hex_dump_internal(), and pkt_dump_internal().

#define PRINT_HEX	(	a,
		b
	)	av_log(s->avctx, AV_LOG_DEBUG, " %s = %x\n", a, b);

Referenced by dump_context().

Function Documentation

static av_cold void dump_context ( WMAProDecodeCtx * s )

static

helper function to print the most important members of the context

Parameters

s context

Definition at line 237 of file wmaprodec.c.

Referenced by decode_init().

static av_cold int decode_end ( AVCodecContext * avctx )

static

Uninitialize the decoder and free all resources.

Parameters

avctx codec context

Returns: 0 on success, < 0 otherwise

Definition at line 256 of file wmaprodec.c.

static av_cold int decode_init ( AVCodecContext * avctx )

static

Initialize the decoder.

Parameters

avctx codec context

Returns: 0 on success, -1 otherwise

dump the extradata

generic init

frame info

get frame len

subframe info

init previous block len

extract lfe channel position

calculate number of scale factor bands and their offsets for every possible block size

Scale factors can be shared between blocks of different size as every block has a different scale factor band layout. The matrix sf_offsets is needed to find the correct scale factor.

init MDCT, FIXME: only init needed sizes

init MDCT windows: simple sine window

calculate subwoofer cutoff values

calculate sine values for the decorrelation matrix

Definition at line 272 of file wmaprodec.c.

static int decode_subframe_length	(	WMAProDecodeCtx *	s,
		int	offset
	)

static

Decode the subframe length.

Parameters

s	context
offset	sample offset in the frame

Returns: decoded subframe length on success, < 0 in case of an error

no need to read from the bitstream when only one length is possible

1 bit indicates if the subframe is of maximum length

sanity check the length

Definition at line 494 of file wmaprodec.c.

Referenced by decode_tilehdr().

static int decode_tilehdr ( WMAProDecodeCtx * s )

static

Decode how the data in the frame is split into subframes.

   Every WMA frame contains the encoded data for a fixed number of
   samples per channel. The data for every channel might be split
   into several subframes. This function will reconstruct the list of
   subframes for every channel.

   If the subframes are not evenly split, the algorithm estimates the
   channels with the lowest number of total samples.
   Afterwards, for each of these channels a bit is read from the
   bitstream that indicates if the channel contains a subframe with the
   next subframe size that is going to be read from the bitstream or not.
   If a channel contains such a subframe, the subframe size gets added to
   the channel's subframe list.
   The algorithm repeats these steps until the frame is properly divided
   between the individual channels.

Parameters

s context

Returns: 0 on success, < 0 in case of an error

< sum of samples for all currently known subframes of a channel

< flag indicating if a channel contains the current subframe

< number of channels that contain the current subframe

< flag indicating that all channels use the same subframe offsets and sizes

< smallest sum of samples (channels with this length will be processed first)

reset tiling information

loop until the frame data is split between the subframes

check which channels contain the subframe

get subframe length, subframe_len == 0 is not allowed

add subframes to the individual channels and find new min_channel_len

Definition at line 545 of file wmaprodec.c.

Referenced by decode_frame().

static void decode_decorrelation_matrix	(	WMAProDecodeCtx *	s,
		WMAProChannelGrp *	chgroup
	)

static

Calculate a decorrelation matrix from the bitstream parameters.

Parameters

s	codec context
chgroup	channel group for which the matrix needs to be calculated

Definition at line 636 of file wmaprodec.c.

Referenced by decode_channel_transform().

static int decode_channel_transform ( WMAProDecodeCtx * s )

static

Decode channel transformation parameters.

Parameters

s	codec context

Returns: >= 0 in case of success, < 0 in case of bitstream errors

in the one channel case channel transforms are pointless

decode channel mask

decode transform type

cos(pi/4)

FIXME: more than 6 coupled channels not supported

decode transform on / off

transform can be enabled for individual bands

Definition at line 686 of file wmaprodec.c.

Referenced by decode_subframe().

static int decode_coeffs	(	WMAProDecodeCtx *	s,
		int	c
	)

static

Extract the coefficients from the bitstream.

Parameters

s	codec context
c	current channel number

Returns: 0 on success, < 0 in case of bitstream errors

decode vector coefficients (consumes up to 167 bits per iteration for 4 vector coded large values)

decode sign

switch to run level mode when subframe_len / 128 zeros were found in a row

decode run level coded coefficients

Definition at line 800 of file wmaprodec.c.

Referenced by decode_subframe().

static int decode_scale_factors ( WMAProDecodeCtx * s )

static

Extract scale factors from the bitstream.

Parameters

s	codec context

Returns: 0 on success, < 0 in case of bitstream errors

should never consume more than 5344 bits MAX_CHANNELS * (1 + MAX_BANDS * 23)

resample scale factors for the new block size as the scale factors might need to be resampled several times before some new values are transmitted, a backup of the last transmitted scale factors is kept in saved_scale_factors

decode DPCM coded scale factors

run level decode differences to the resampled factors

swap buffers

calculate new scale factor maximum

Definition at line 903 of file wmaprodec.c.

Referenced by decode_subframe().

static void inverse_channel_transform ( WMAProDecodeCtx * s )

static

Reconstruct the individual channel data.

Parameters

s	codec context

multichannel decorrelation

multiply values with the decorrelation_matrix

Definition at line 996 of file wmaprodec.c.

Referenced by decode_subframe().

static void wmapro_window ( WMAProDecodeCtx * s )

static

Apply sine window and reconstruct the output buffer.

Parameters

s	codec context

Definition at line 1051 of file wmaprodec.c.

Referenced by decode_subframe().

static int decode_subframe ( WMAProDecodeCtx * s )

static

Decode a single subframe (block).

Parameters

s	codec context

Returns: 0 on success, < 0 when decoding failed

reset channel context and find the next block offset and size == the next block of the channel with the smallest number of decoded samples

get a list of all channels that contain the estimated block

subtract already processed samples

and count if there are multiple subframes that match our profile

check if the frame will be complete after processing the estimated block

calculate number of scale factor bands and their offsets

configure the decoder for the current subframe

skip extended header if any

no idea for what the following bit is used

decode number of vector coded coefficients

decode quantization step

decode quantization step modifiers for every channel

decode scale factors

parse coefficients

reconstruct the per channel data

inverse quantization and rescaling

apply imdct (imdct_half == DCTIV with reverse)

window and overlapp-add

handled one subframe

Definition at line 1081 of file wmaprodec.c.

Referenced by decode_frame().

static int decode_frame	(	WMAProDecodeCtx *	s,
		AVFrame *	frame,
		int *	got_frame_ptr
	)

static

Decode one WMA frame.

Parameters

s	codec context

Returns: 0 if the trailer bit indicates that this is the last frame, 1 if there are additional frames

get frame length

decode tile information

read postproc transform

read drc info

no idea what these are for, might be the number of samples that need to be skipped at the beginning or end of a stream

usually true for the first frame

sometimes true for the last frame

reset subframe states

decode all subframes

copy samples to the output buffer

reuse second half of the IMDCT output for the next frame

FIXME: not sure if this is always an error

skip the rest of the frame data

decode trailer bit

Definition at line 1321 of file wmaprodec.c.

Referenced by decode_packet().

static int remaining_bits	(	WMAProDecodeCtx *	s,
		GetBitContext *	gb
	)

static

Calculate remaining input buffer length.

Parameters

s	codec context
gb	bitstream reader context

Returns: remaining size in bits

Definition at line 1450 of file wmaprodec.c.

Referenced by decode_packet().

static void save_bits	(	WMAProDecodeCtx *	s,
		GetBitContext *	gb,
		int	len,
		int	append
	)

static

Fill the bit reservoir with a (partial) frame.

Parameters

s	codec context
gb	bitstream reader context
len	length of the partial frame
append	decides whether to reset the buffer or not

when the frame data does not need to be concatenated, the input buffer is reset and additional bits from the previous frame are copied and skipped later so that a fast byte copy is possible

Definition at line 1462 of file wmaprodec.c.

Referenced by decode_packet().

static int decode_packet	(	AVCodecContext *	avctx,
		void *	data,
		int *	got_frame_ptr,
		AVPacket *	avpkt
	)

static

Decode a single WMA packet.

Parameters

avctx	codec context
data	the output buffer
avpkt	input packet

Returns: number of bytes that were read from the input buffer

sanity check for the buffer length

parse packet header

get number of bits that need to be added to the previous frame

check for packet loss

append the previous frame data to the remaining data from the previous packet to create a full frame

decode the cross packet frame if it is valid

reset number of saved bits so that the decoder does not start to decode incomplete frames in the s->len_prefix == 0 case

when the frames do not have a length prefix, we don't know the compressed length of the individual frames however, we know what part of a new packet belongs to the previous frame therefore we save the incoming packet first, then we append the "previous frame" data from the next packet so that we get a buffer that only contains full frames

save the rest of the data so that it can be decoded with the next packet

Definition at line 1516 of file wmaprodec.c.

static void flush ( AVCodecContext * avctx )

static

Clear decoder buffers (for seeking).

Parameters

avctx codec context

reset output buffer as a part of it is used during the windowing of a new frame

Definition at line 1633 of file wmaprodec.c.

Variable Documentation

VLC sf_vlc

static

scale factor DPCM vlc

Definition at line 122 of file wmaprodec.c.

VLC sf_rl_vlc

static

scale factor run length vlc

Definition at line 123 of file wmaprodec.c.

VLC vec4_vlc

static

4 coefficients per symbol

Definition at line 124 of file wmaprodec.c.

VLC vec2_vlc

static

2 coefficients per symbol

Definition at line 125 of file wmaprodec.c.

VLC vec1_vlc

static

1 coefficient per symbol

Definition at line 126 of file wmaprodec.c.

VLC coef_vlc[2]

static

coefficient run length vlc codes

Definition at line 127 of file wmaprodec.c.

float sin64[33]

static

sine table for decorrelation

Definition at line 128 of file wmaprodec.c.

Referenced by decode_decorrelation_matrix(), and decode_init().

AVCodec ff_wmapro_decoder

Initial value:

= {
    .name           = "wmapro",
    .long_name      = NULL_IF_CONFIG_SMALL("Windows Media Audio 9 Professional"),
    .type           = AVMEDIA_TYPE_AUDIO,
    .id             = AV_CODEC_ID_WMAPRO,
    .priv_data_size = sizeof(WMAProDecodeCtx),
    .init           = decode_init,
    .close          = decode_end,
    .decode         = decode_packet,
    .capabilities   = CODEC_CAP_SUBFRAMES | CODEC_CAP_DR1,
    .flush          = flush,
    .sample_fmts    = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_FLTP,
                                                      AV_SAMPLE_FMT_NONE },
}

wmapro decoder

Definition at line 1649 of file wmaprodec.c.

Data Structures

Macros

Functions

Variables

Detailed Description

|| packet 0 || packet 1 || packet 2 packets

|| frame 0 || frame 1 || frame 2 || frames

|| | | || | | | || || subframes of channel 0

|| | | || | | | || || subframes of channel 1

Macro Definition Documentation

Function Documentation

Variable Documentation