omxacmp3_unpackframeheader.c

The OpenMAX DL (Development Layer) APIs contain a comprehensive set of audio, video, signal processi

/**
 * 
 * File Name:  omxACMP3_UnpackFrameHeader.c
 * OpenMAX DL: v1.0.2
 * Revision:   10586
 * Date:       Wednesday, March 5, 2008
 * 
 * (c) Copyright 2007-2008 ARM Limited. All Rights Reserved.
 * 
 * 
 * Description: This function is used to unpack a 32 bit mp3 frame header
 * as defined in ISO/IEC 13818-3
 */

#include "omxtypes.h"
#include "armOMX.h"
#include "omxAC.h"
#include "armCOMM.h"

#define ARM_MP3_IDEX_MASK       (0x00100000) 
#define ARM_MP3_ID_MASK         (0x00080000)
#define ARM_MP3_LAYER_MASK      (0x00060000)
#define ARM_MP3_PROTBIT_MASK    (0x00010000)
#define ARM_MP3_BITRATE_MASK    (0x0000F000)
#define ARM_MP3_SAMPFREQ_MASK   (0x00000C00)
#define ARM_MP3_PADFLAG_MASK    (0x00000200)
#define ARM_MP3_PRIVBIT_MASK    (0x00000100)
#define ARM_MP3_MODE_MASK       (0x000000C0)
#define ARM_MP3_MODEEXT_MASK    (0x00000030)
#define ARM_MP3_COPYRIGHT_MASK  (0x00000008)
#define ARM_MP3_ORIGCOPY_MASK   (0x00000004)
#define ARM_MP3_EMPHASIS_MASK   (0x00000003)

#define ARM_MP3_IDEX_SHIFT      (20)
#define ARM_MP3_ID_SHIFT        (19)
#define ARM_MP3_LAYER_SHIFT     (17)
#define ARM_MP3_PROTBIT_SHIFT   (16)
#define ARM_MP3_BITRATE_SHIFT   (12)
#define ARM_MP3_SAMPFREQ_SHIFT  (10)
#define ARM_MP3_PADFLAG_SHIFT   (9)
#define ARM_MP3_PRIVBIT_SHIFT   (8)
#define ARM_MP3_MODE_SHIFT      (6)
#define ARM_MP3_MODEEXT_SHIFT   (4)
#define ARM_MP3_COPYRIGHT_SHIFT (3)
#define ARM_MP3_ORIGCOPY_SHIFT  (2)
#define ARM_MP3_EMPHASIS_SHIFT  (0)

/**
 * Function:  omxACMP3_UnpackFrameHeader   (3.1.3.1.1)
 *
 * Description:
 * Unpacks the audio frame header. If CRC is enabled, this function also 
 * unpacks the CRC word. Before calling omxACMP3_UnpackFrameHeader, the 
 * decoder application should locate the bit stream sync word and ensure that 
 * *ppBitStream points to the first byte of the 32-bit frame header. If CRC is 
 * enabled, it is assumed that the 16-bit CRC word is adjacent to the 32-bit 
 * frame header, as defined in the MP3 standard. Before returning to the 
 * caller, the function updates the pointer *ppBitStream, such that it 
 * references the next byte after the frame header or the CRC word. The first 
 * byte of the 16-bit CRC word is stored in pFrameHeader->CRCWord[15:8], and 
 * the second byte is stored in pFrameHeader->CRCWord[7:0]. The function does 
 * not detect corrupted frame headers. Reference [ISO13818-3], sub-clause 
 * 2.4.2.3 
 *
 * Input Arguments:
 *   
 *   ppBitStream - double pointer to the first byte of the MP3 frame header 
 *
 * Output Arguments:
 *   
 *   pFrameHeader - pointer to the MP3 frame header structure (defined in 
 *            section  Data Structures ) 
 *   ppBitStream - double pointer to the byte immediately following the frame 
 *            header 
 *
 * Return Value:
 *    
 *    OMX_Sts_NoErr - no error 
 *    OMX_Sts_BadArgErr - invalid arguments - either ppBitStream, 
 *              pFrameHeader, or *ppBitStream is NULL 
 *
 */
OMXResult omxACMP3_UnpackFrameHeader (
     const OMX_U8 **ppBitStream,
     OMXMP3FrameHeader *pFrameHeader
 )
{
    OMX_U32     Mp3Header;
    OMX_U8      *pBitStream; 

    /* Arguments check */
    armRetArgErrIf(ppBitStream == NULL, OMX_Sts_BadArgErr)
    armRetArgErrIf(pFrameHeader == NULL, OMX_Sts_BadArgErr)
    armRetArgErrIf(*ppBitStream == NULL, OMX_Sts_BadArgErr)
    
    pBitStream = (OMX_U8 *)*ppBitStream; 

    /* get 32 bit header */
    Mp3Header = (OMX_U32) pBitStream [0];
    Mp3Header = (Mp3Header << 8) | (OMX_U32) pBitStream [1];
    Mp3Header = (Mp3Header << 8) | (OMX_U32) pBitStream [2];
    Mp3Header = (Mp3Header << 8) | (OMX_U32) pBitStream [3];

    /* Fill struct with header fields */
    pFrameHeader->idEx = 
        (Mp3Header & ARM_MP3_IDEX_MASK) >> ARM_MP3_IDEX_SHIFT;
    pFrameHeader->id = 
        (Mp3Header & ARM_MP3_ID_MASK) >> ARM_MP3_ID_SHIFT;
    pFrameHeader->layer = 
        (Mp3Header & ARM_MP3_LAYER_MASK) >> ARM_MP3_LAYER_SHIFT;
    pFrameHeader->protectionBit = 
        (Mp3Header & ARM_MP3_PROTBIT_MASK) >> ARM_MP3_PROTBIT_SHIFT;
    pFrameHeader->bitRate = 
        (Mp3Header & ARM_MP3_BITRATE_MASK) >> ARM_MP3_BITRATE_SHIFT;
    pFrameHeader->samplingFreq = 
        (Mp3Header & ARM_MP3_SAMPFREQ_MASK) >> ARM_MP3_SAMPFREQ_SHIFT;
    pFrameHeader->paddingBit = 
        (Mp3Header & ARM_MP3_PADFLAG_MASK) >> ARM_MP3_PADFLAG_SHIFT;
    pFrameHeader->privateBit = 
        (Mp3Header & ARM_MP3_PRIVBIT_MASK) >> ARM_MP3_PRIVBIT_SHIFT;
    pFrameHeader->mode = 
        (Mp3Header & ARM_MP3_MODE_MASK) >> ARM_MP3_MODE_SHIFT;
    pFrameHeader->modeExt = 
        (Mp3Header & ARM_MP3_MODEEXT_MASK) >> ARM_MP3_MODEEXT_SHIFT;
    pFrameHeader->copyright = 
        (Mp3Header & ARM_MP3_COPYRIGHT_MASK) >> ARM_MP3_COPYRIGHT_SHIFT;
    pFrameHeader->originalCopy = 
        (Mp3Header & ARM_MP3_ORIGCOPY_MASK) >> ARM_MP3_ORIGCOPY_SHIFT;
    pFrameHeader->emphasis = 
        (Mp3Header & ARM_MP3_EMPHASIS_MASK) >> ARM_MP3_EMPHASIS_SHIFT;
    
    /* update bit stream pointer */
    *ppBitStream += 4;
    pBitStream = (OMX_U8 *)*ppBitStream; 

    /* Check for presence of CRC */
    if (pFrameHeader->protectionBit == 0)
    {
        /* Read 32 bit CRC */
        pFrameHeader->CRCWord = 
            ((OMX_INT) pBitStream [0] << 8) | (OMX_INT) pBitStream [1];
        *ppBitStream += 2;
    }

    return OMX_Sts_NoErr;
}

/*****************************************************************************
 *                              END OF FILE
 *****************************************************************************/