DECODER.CPP

//==========================================================================; 
// 
//  THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY 
//  KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE 
//  IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR 
//  PURPOSE. 
// 
//  Copyright (c) 1992 - 1997  Microsoft Corporation.  All Rights Reserved. 
// 
//--------------------------------------------------------------------------; 
// 
/******************************Module*Header*******************************\ 
* Module Name: Decoder.cpp 
* 
* Implements a prototype Mpeg Audio Software codec.  It just consumes 
* the passed in audio frames. 
* 
* 
\**************************************************************************/ 
#include "MpgAudio.h" 
 
 
 
/* ------------------------------------------------------------------------- 
** CAudioDecoder 
** ------------------------------------------------------------------------- 
*/ 
 
/******************************Public*Routine******************************\ 
* CAudioDecoder 
* 
* Constructor and destructor 
* 
* 
\**************************************************************************/ 
CAudioDecoder::CAudioDecoder(CMpegAudioCodec *pMpegCodec) 
    : m_pCodec(pMpegCodec) {} 
 
 
 
/******************************Public*Routine******************************\ 
* ResetAudio 
* 
* 
\**************************************************************************/ 
DWORD 
CAudioDecoder::ResetAudio() 
{ 
    CAutoLock lck(this); 
    return DECODE_SUCCESS; 
} 
 
 
/******************************Public*Routine******************************\ 
* DecodeFrame 
* 
* 
\**************************************************************************/ 
DWORD 
CAudioDecoder::DecodeAudioFrame( 
    AudioCtrl *pCtrl 
    ) 
{ 
    CAutoLock   lck(this); 
    DWORD       rc = DECODE_SUCCESS; 
 
    m_pCtrl = pCtrl; 
 
 
    for (DWORD i = 0; i < m_pCtrl->dwNumFrames; i++) { 
 
        // Skip the sync word 
        m_pCtrl->pCmprRead += 2; 
 
        // skip the rest of the frame 
        if (!SkipFrame()) { 
            m_pCtrl->dwOutBuffUsed = 0L; 
            return DECODE_ERR_DATA; 
        } 
    } 
 
    ZeroMemory(m_pCtrl->pOutBuffer, m_pCtrl->dwOutBuffSize); 
    m_pCtrl->dwOutBuffUsed = m_pCtrl->dwOutBuffSize; 
 
    return rc; 
} 
 
 
/*****************************Private*Routine******************************\ 
* SkipFrame 
* 
* 
\**************************************************************************/ 
BOOL 
CAudioDecoder::SkipFrame() 
{ 
    LPBYTE  lpCurr = m_pCtrl->pCmprRead; 
    LPBYTE  lpEnd = m_pCtrl->pCmprWrite; 
    int sm = 0; 
 
    while (lpCurr < lpEnd && sm < 2)  { 
 
        switch (sm) { 
        case 0: 
            sm = (*lpCurr == 0xff); 
            break; 
 
        case 1: 
            if ((*lpCurr & 0xf0) == 0xf0) sm = 2; /* sync found */ 
            else sm = (*lpCurr == 0xff); 
            break; 
        } 
        lpCurr++; 
    } 
 
    // 
    // When we get here we have either run out of buffer or found the first 
    // "sm" bytes of a valid sync word. 
    // 
    // Don't forget to put back the sync word bytes that we have just 
    // read otherwise they would be lost forever. 
    // 
    lpCurr -= sm; 
    m_pCtrl->pCmprRead = lpCurr; 
 
    if (sm < 2) { 
        return FALSE;   // sync not found. 
    } 
 
    return TRUE; 
}