libavcodec/wmaprodec.c File Reference

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

#include "avcodec.h"
#include "internal.h"
#include "get_bits.h"
#include "put_bits.h"
#include "wmaprodata.h"
#include "dsputil.h"
#include "wma.h"

Go to the source code of this file.

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...

Defines

#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_MAX_BITS   12
 log2 of max block size
#define WMAPRO_BLOCK_MAX_SIZE   (1 << WMAPRO_BLOCK_MAX_BITS)
 maximum block size
#define WMAPRO_BLOCK_SIZES   (WMAPRO_BLOCK_MAX_BITS - 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 void av_cold 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)
 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 *data_size, 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]
 sinus table for decorrelation
AVCodec 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:

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.


Define Documentation

#define MAX_BANDS   29

max number of scale factor bands

Definition at line 100 of file wmaprodec.c.

Referenced by decode_init().

#define MAX_FRAMESIZE   32768

#define MAX_SUBFRAMES   32

max number of subframes per channel

Definition at line 99 of file wmaprodec.c.

Referenced by decode_init(), and decode_tilehdr().

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

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

Referenced by dump_context().

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

Definition at line 113 of file wmaprodec.c.

Referenced by decode_scale_factors().

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

Definition at line 114 of file wmaprodec.c.

Referenced by decode_scale_factors().

#define SCALEVLCBITS   8

Definition at line 109 of file wmaprodec.c.

Referenced by decode_init(), and decode_scale_factors().

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

Definition at line 112 of file wmaprodec.c.

Referenced by decode_coeffs().

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

Definition at line 111 of file wmaprodec.c.

Referenced by decode_coeffs().

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

Definition at line 110 of file wmaprodec.c.

Referenced by decode_coeffs().

#define VLCBITS   9

Definition at line 108 of file wmaprodec.c.

#define WMAPRO_BLOCK_MAX_BITS   12

log2 of max block size

Definition at line 103 of file wmaprodec.c.

Referenced by decode_init().

#define WMAPRO_BLOCK_MAX_SIZE   (1 << WMAPRO_BLOCK_MAX_BITS)

maximum block size

Definition at line 104 of file wmaprodec.c.

#define WMAPRO_BLOCK_SIZES   (WMAPRO_BLOCK_MAX_BITS - BLOCK_MIN_BITS + 1)

possible block sizes

Definition at line 105 of file wmaprodec.c.

Referenced by decode_end(), and decode_init().

#define WMAPRO_MAX_CHANNELS   8

current decoder limitations

max number of handled channels

Definition at line 98 of file wmaprodec.c.

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


Function Documentation

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 652 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 765 of file wmaprodec.c.

Referenced by decode_subframe().

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 602 of file wmaprodec.c.

Referenced by decode_channel_transform().

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 250 of file wmaprodec.c.

static int decode_frame ( WMAProDecodeCtx s  )  [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

check for potential output buffer overflow

return an error if no frame could be decoded at all

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

interleave samples and write them 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 1268 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

skip first frame

get frame len

init previous block len

subframe info

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 sinus window

calculate subwoofer cutoff values

calculate sine values for the decorrelation matrix

Definition at line 266 of file wmaprodec.c.

static int decode_packet ( AVCodecContext avctx,
void *  data,
int *  data_size,
AVPacket avpkt 
) [static]

Decode a single WMA packet.

Parameters:
avctx codec context
data the output buffer
data_size number of bytes that were written to 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

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

Definition at line 1460 of file wmaprodec.c.

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 867 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

substract 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

FIXME: might change run level mode decision

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 (ff_imdct_half == DCTIV with reverse)

window and overlapp-add

handled one subframe

Definition at line 1045 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 461 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 509 of file wmaprodec.c.

Referenced by decode_frame().

static void av_cold dump_context ( WMAProDecodeCtx s  )  [static]

helper function to print the most important members of the context

Parameters:
s context

Definition at line 231 of file wmaprodec.c.

Referenced by decode_init().

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 1551 of file wmaprodec.c.

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 960 of file wmaprodec.c.

Referenced by decode_subframe().

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 1395 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 wether to reset the buffer or not

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

Definition at line 1407 of file wmaprodec.c.

Referenced by decode_packet().

static void wmapro_window ( WMAProDecodeCtx s  )  [static]

Apply sine window and reconstruct the output buffer.

Parameters:
s codec context

Definition at line 1015 of file wmaprodec.c.

Referenced by decode_subframe().


Variable Documentation

VLC coef_vlc[2] [static]

coefficient run length vlc codes

Definition at line 121 of file wmaprodec.c.

VLC sf_rl_vlc [static]

scale factor run length vlc

Definition at line 117 of file wmaprodec.c.

VLC sf_vlc [static]

scale factor DPCM vlc

Definition at line 116 of file wmaprodec.c.

float sin64[33] [static]

sinus table for decorrelation

Definition at line 122 of file wmaprodec.c.

Referenced by decode_decorrelation_matrix(), and decode_init().

VLC vec1_vlc [static]

1 coefficient per symbol

Definition at line 120 of file wmaprodec.c.

VLC vec2_vlc [static]

2 coefficients per symbol

Definition at line 119 of file wmaprodec.c.

VLC vec4_vlc [static]

4 coefficients per symbol

Definition at line 118 of file wmaprodec.c.

Initial value:

 {
    "wmapro",
    AVMEDIA_TYPE_AUDIO,
    CODEC_ID_WMAPRO,
    sizeof(WMAProDecodeCtx),
    decode_init,
    NULL,
    decode_end,
    decode_packet,
    .capabilities = CODEC_CAP_SUBFRAMES,
    .flush= flush,
    .long_name = NULL_IF_CONFIG_SMALL("Windows Media Audio 9 Professional"),
}
wmapro decoder

Definition at line 1567 of file wmaprodec.c.


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