pvmp3_decode_header.cpp
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/* ------------------------------------------------------------------
* Copyright (C) 1998-2009 PacketVideo
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied.
* See the License for the specific language governing permissions
* and limitations under the License.
* -------------------------------------------------------------------
*/
/*
------------------------------------------------------------------------------
PacketVideo Corp.
MP3 Decoder Library
Filename: pvmp3_decode_header.cpp
Date: 09/21/2007
------------------------------------------------------------------------------
REVISION HISTORY
Description:
------------------------------------------------------------------------------
INPUT AND OUTPUT DEFINITIONS
Input
tbits *inputStream, bit stream
mp3Header *info,
uint32 *crc
Returns
mp3Header *info, structure holding the parsed mp3 header info
uint32 *crc initialized crc computation
------------------------------------------------------------------------------
FUNCTION DESCRIPTION
gets mp3 header information
------------------------------------------------------------------------------
REQUIREMENTS
------------------------------------------------------------------------------
REFERENCES
[1] ISO MPEG Audio Subgroup Software Simulation Group (1996)
ISO 13818-3 MPEG-2 Audio Decoder - Lower Sampling Frequency Extension
------------------------------------------------------------------------------
PSEUDO-CODE
------------------------------------------------------------------------------
*/
/*----------------------------------------------------------------------------
; INCLUDES
----------------------------------------------------------------------------*/
#include "pvmp3_decode_header.h"
#include "pvmp3_crc.h"
#include "pvmp3_getbits.h"
#include "pvmp3_seek_synch.h"
/*----------------------------------------------------------------------------
; MACROS
; Define module specific macros here
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; DEFINES
; Include all pre-processor statements here. Include conditional
; compile variables also.
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL FUNCTION DEFINITIONS
; Function Prototype declaration
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL STORE/BUFFER/POINTER DEFINITIONS
; Variable declaration - defined here and used outside this module
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; EXTERNAL FUNCTION REFERENCES
; Declare functions defined elsewhere and referenced in this module
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES
; Declare variables used in this module but defined elsewhere
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; FUNCTION CODE
----------------------------------------------------------------------------*/
ERROR_CODE pvmp3_decode_header(tmp3Bits *inputStream,
mp3Header *info,
uint32 *crc)
{
ERROR_CODE err = NO_DECODING_ERROR;
uint32 temp;
/*
* Verify that at least the header is complete
* Note that SYNC_WORD_LNGTH is in unit of bits, but inputBufferCurrentLength
* is in unit of bytes.
*/
if (inputStream->inputBufferCurrentLength < ((SYNC_WORD_LNGTH + 21) >> 3))
{
return NO_ENOUGH_MAIN_DATA_ERROR;
}
/*
* MPEG Audio Version ID
*/
temp = getUpTo17bits(inputStream, SYNC_WORD_LNGTH);
if ((temp & SYNC_WORD) != SYNC_WORD)
{
err = pvmp3_header_sync(inputStream);
if (err != NO_DECODING_ERROR)
{
return err;
}
}
temp = getNbits(inputStream, 21); // to avoid multiple bitstream accesses
switch (temp >> 19) /* 2 */
{
case 0:
info->version_x = MPEG_2_5;
break;
case 2:
info->version_x = MPEG_2;
break;
case 3:
info->version_x = MPEG_1;
break;
default:
info->version_x = INVALID_VERSION;
err = UNSUPPORTED_LAYER;
break;
}
info->layer_description = 4 - ((temp << 13) >> 30); /* 2 */
info->error_protection = !((temp << 15) >> 31); /* 1 */
if (info->error_protection)
{
*crc = 0xffff; /* CRC start value */
calculate_crc((temp << 16) >> 16, 16, crc);
}
info->bitrate_index = (temp << 16) >> 28; /* 4 */
info->sampling_frequency = (temp << 20) >> 30; /* 2 */
info->padding = (temp << 22) >> 31; /* 1 */
info->extension = (temp << 23) >> 31; /* 1 */
info->mode = (temp << 24) >> 30; /* 2 */
info->mode_ext = (temp << 26) >> 30; /* 2 */
info->copyright = (temp << 27) >> 31; /* 1 */
info->original = (temp << 28) >> 31; /* 1 */
info->emphasis = (temp << 30) >> 30; /* 2 */
if (!info->bitrate_index || info->sampling_frequency == 3)
{
err = UNSUPPORTED_FREE_BITRATE;
}
return(err);
}