FFmpeg
libavcodec
mpegaudiodecheader.c
Go to the documentation of this file.
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/*
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* MPEG Audio header decoder
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* Copyright (c) 2001, 2002 Fabrice Bellard
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file
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* MPEG Audio header decoder.
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*/
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#include "
libavutil/macros.h
"
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#include "
mpegaudio.h
"
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#include "
mpegaudiodata.h
"
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#include "
mpegaudiodecheader.h
"
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int
avpriv_mpegaudio_decode_header
(
MPADecodeHeader
*
s
, uint32_t
header
)
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{
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int
sample_rate,
frame_size
, mpeg25, padding;
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int
sample_rate_index, bitrate_index;
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int
ret
;
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ret
=
ff_mpa_check_header
(
header
);
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if
(
ret
< 0)
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return
ret
;
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if
(
header
& (1<<20)) {
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s
->lsf = (
header
& (1<<19)) ? 0 : 1;
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mpeg25 = 0;
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}
else
{
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s
->lsf = 1;
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mpeg25 = 1;
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}
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s
->layer = 4 - ((
header
>> 17) & 3);
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/* extract frequency */
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sample_rate_index = (
header
>> 10) & 3;
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if
(sample_rate_index >=
FF_ARRAY_ELEMS
(
ff_mpa_freq_tab
))
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sample_rate_index = 0;
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sample_rate =
ff_mpa_freq_tab
[sample_rate_index] >> (
s
->lsf + mpeg25);
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sample_rate_index += 3 * (
s
->lsf + mpeg25);
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s
->sample_rate_index = sample_rate_index;
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s
->error_protection = ((
header
>> 16) & 1) ^ 1;
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s
->sample_rate = sample_rate;
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bitrate_index = (
header
>> 12) & 0
xf
;
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padding = (
header
>> 9) & 1;
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//extension = (header >> 8) & 1;
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s
->mode = (
header
>> 6) & 3;
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s
->mode_ext = (
header
>> 4) & 3;
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//copyright = (header >> 3) & 1;
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//original = (header >> 2) & 1;
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//emphasis = header & 3;
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if
(
s
->mode ==
MPA_MONO
)
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s
->nb_channels = 1;
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else
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s
->nb_channels = 2;
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if
(bitrate_index != 0) {
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frame_size
=
ff_mpa_bitrate_tab
[
s
->lsf][
s
->layer - 1][bitrate_index];
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s
->bit_rate =
frame_size
* 1000;
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switch
(
s
->layer) {
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case
1:
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frame_size
= (
frame_size
* 12000) / sample_rate;
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frame_size
= (
frame_size
+ padding) * 4;
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break
;
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case
2:
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frame_size
= (
frame_size
* 144000) / sample_rate;
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frame_size
+= padding;
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break
;
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default
:
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case
3:
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frame_size
= (
frame_size
* 144000) / (sample_rate <<
s
->lsf);
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frame_size
+= padding;
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break
;
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}
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s
->frame_size =
frame_size
;
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}
else
{
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/* if no frame size computed, signal it */
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return
1;
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}
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#if defined(DEBUG)
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ff_dlog
(
NULL
,
"layer%d, %d Hz, %d kbits/s, "
,
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s
->layer,
s
->sample_rate,
s
->bit_rate);
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if
(
s
->nb_channels == 2) {
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if
(
s
->layer == 3) {
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if
(
s
->mode_ext &
MODE_EXT_MS_STEREO
)
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ff_dlog
(
NULL
,
"ms-"
);
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if
(
s
->mode_ext &
MODE_EXT_I_STEREO
)
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ff_dlog
(
NULL
,
"i-"
);
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}
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ff_dlog
(
NULL
,
"stereo"
);
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}
else
{
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ff_dlog
(
NULL
,
"mono"
);
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}
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ff_dlog
(
NULL
,
"\n"
);
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#endif
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return
0;
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}
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int
ff_mpa_decode_header
(uint32_t head,
int
*sample_rate,
int
*
channels
,
int
*
frame_size
,
int
*bit_rate,
enum
AVCodecID
*
codec_id
)
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{
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MPADecodeHeader
s1, *
s
= &s1;
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if
(
avpriv_mpegaudio_decode_header
(
s
, head) != 0) {
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return
-1;
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}
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switch
(
s
->layer) {
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case
1:
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*
codec_id
=
AV_CODEC_ID_MP1
;
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*
frame_size
= 384;
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break
;
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case
2:
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*
codec_id
=
AV_CODEC_ID_MP2
;
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*
frame_size
= 1152;
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break
;
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default
:
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case
3:
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if
(*
codec_id
!=
AV_CODEC_ID_MP3ADU
)
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*
codec_id
=
AV_CODEC_ID_MP3
;
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if
(
s
->lsf)
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*
frame_size
= 576;
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else
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*
frame_size
= 1152;
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break
;
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}
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*sample_rate =
s
->sample_rate;
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*
channels
=
s
->nb_channels;
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*bit_rate =
s
->bit_rate;
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return
s
->frame_size;
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}
MPA_MONO
#define MPA_MONO
Definition:
mpegaudio.h:49
mpegaudiodecheader.h
MPADecodeHeader
Definition:
mpegaudiodecheader.h:47
AV_CODEC_ID_MP3ADU
@ AV_CODEC_ID_MP3ADU
Definition:
codec_id.h:458
ff_mpa_decode_header
int ff_mpa_decode_header(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
Definition:
mpegaudiodecheader.c:120
macros.h
AV_CODEC_ID_MP3
@ AV_CODEC_ID_MP3
preferred ID for decoding MPEG audio layer 1, 2 or 3
Definition:
codec_id.h:446
avpriv_mpegaudio_decode_header
int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
Definition:
mpegaudiodecheader.c:34
FF_ARRAY_ELEMS
#define FF_ARRAY_ELEMS(a)
Definition:
sinewin_tablegen.c:29
MODE_EXT_MS_STEREO
#define MODE_EXT_MS_STEREO
Definition:
mpegaudiodata.h:37
s
#define s(width, name)
Definition:
cbs_vp9.c:198
frame_size
int frame_size
Definition:
mxfenc.c:2424
AV_CODEC_ID_MP2
@ AV_CODEC_ID_MP2
Definition:
codec_id.h:445
channels
channels
Definition:
aptx.h:31
codec_id
enum AVCodecID codec_id
Definition:
vaapi_decode.c:394
NULL
#define NULL
Definition:
coverity.c:32
AVCodecID
AVCodecID
Identify the syntax and semantics of the bitstream.
Definition:
codec_id.h:49
ff_dlog
#define ff_dlog(a,...)
Definition:
tableprint_vlc.h:28
ff_mpa_check_header
static int ff_mpa_check_header(uint32_t header)
Definition:
mpegaudiodecheader.h:62
header
static const uint8_t header[24]
Definition:
sdr2.c:68
xf
#define xf(width, name, var, range_min, range_max, subs,...)
Definition:
cbs_av1.c:598
mpegaudio.h
ret
ret
Definition:
filter_design.txt:187
MODE_EXT_I_STEREO
#define MODE_EXT_I_STEREO
Definition:
mpegaudiodata.h:38
ff_mpa_freq_tab
const uint16_t ff_mpa_freq_tab[3]
Definition:
mpegaudiotabs.h:37
mpegaudiodata.h
ff_mpa_bitrate_tab
const FF_VISIBILITY_PUSH_HIDDEN uint16_t ff_mpa_bitrate_tab[2][3][15]
Definition:
mpegaudiotabs.h:27
AV_CODEC_ID_MP1
@ AV_CODEC_ID_MP1
Definition:
codec_id.h:487
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