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