
/*****************************************************************
|
|      File: Ap4AdtsParser.c
|
|      AP4 - ADTS Parser
|
|      (c) 2005 Gilles Boccon-Gibod
|      Author: Gilles Boccon-Gibod (bok@bok.net)
|
 ****************************************************************/

/*----------------------------------------------------------------------
|   includes
+---------------------------------------------------------------------*/
#include "Ap4BitStream.h"
#include "Ap4AdtsParser.h"

/*----------------------------------------------------------------------
|   constants
+---------------------------------------------------------------------*/
#define AP4_ADTS_HEADER_SIZE 7

#define AP4_ADTS_SYNC_MASK     0xFFF6 /* 12 sync bits plus 2 layer bits */
#define AP4_ADTS_SYNC_PATTERN  0xFFF0 /* 12 sync bits=1 layer=0         */

const unsigned long  
AP4_AdtsSamplingFrequencyTable[16] =
{
    96000,
    88200,
    64000,
    48000,
    44100,
    32000,
    24000,
    22050,
    16000,
    12000,
    11025,
    8000,
    7350,
    0,      /* Reserved */
    0,      /* Reserved */
    0       /* Escape code */
};

/*----------------------------------------------------------------------+
|    AP4_AdtsHeader::AP4_AdtsHeader
+----------------------------------------------------------------------*/
AP4_AdtsHeader::AP4_AdtsHeader(const AP4_UI08* bytes)
{
    // fixed part
    m_Id                     = ( bytes[1] & 0x08) >> 3;
    m_ProtectionAbsent       =   bytes[1] & 0x01;
    m_ProfileObjectType      = ( bytes[2] & 0xC0) >> 6;
    m_SamplingFrequencyIndex = ( bytes[2] & 0x3C) >> 2;
    m_ChannelConfiguration   = ((bytes[2] & 0x01) << 2) | 
                               ((bytes[3] & 0xC0) >> 6);
    // variable part
    m_FrameLength = ((unsigned int)(bytes[3] & 0x03) << 11) |
                    ((unsigned int)(bytes[4]       ) <<  3) |
                    ((unsigned int)(bytes[5] & 0xE0) >>  5);
    m_RawDataBlocks =               bytes[6] & 0x03;
}

/*----------------------------------------------------------------------+
|    AP4_AdtsHeader::MatchFixed
|
|    Check that two fixed headers are the same
|
+----------------------------------------------------------------------*/
bool
AP4_AdtsHeader::MatchFixed(unsigned char* a, unsigned char* b)
{
    if (a[0]         ==  b[0] &&
        a[1]         ==  b[1] &&
        a[2]         ==  b[2] &&
       (a[3] & 0xF0) == (b[3] & 0xF0)) {
        return true;
    } else {
        return false;
    }
}

/*----------------------------------------------------------------------+
|    AP4_AdtsHeader::Check
+----------------------------------------------------------------------*/
AP4_Result
AP4_AdtsHeader::Check()
{
    // check that the sampling frequency index is valid
    if (m_SamplingFrequencyIndex >= 0xD) {
        return AP4_FAILURE;
    }

    /* MPEG2 does not use all profiles */
    if (m_Id == 1 && m_ProfileObjectType == 3) {
        return AP4_FAILURE;
    }

    return AP4_SUCCESS;
}

/*----------------------------------------------------------------------+
|    AP4_AdtsParser::AP4_AdtsParser
+----------------------------------------------------------------------*/
AP4_AdtsParser::AP4_AdtsParser()
{
}

/*----------------------------------------------------------------------+
|    AP4_AdtsParser::~AP4_AdtsParser
+----------------------------------------------------------------------*/
AP4_AdtsParser::~AP4_AdtsParser()
{
}

/*----------------------------------------------------------------------+
|    AP4_AdtsParser::Reset
+----------------------------------------------------------------------*/
AP4_Result
AP4_AdtsParser::Reset()
{
    m_FrameCount = 0;

    return AP4_SUCCESS;
}

/*----------------------------------------------------------------------+
|    AP4_AdtsParser::Feed
+----------------------------------------------------------------------*/
AP4_Result
AP4_AdtsParser::Feed(const AP4_UI08* buffer, 
                     AP4_Size*       buffer_size,
                     AP4_Flags       flags)
{
    AP4_Size free_space;

    /* update flags */
    m_Bits.m_Flags = flags;

    /* possible shortcut */
    if (buffer == NULL ||
        buffer_size == NULL || 
        *buffer_size == 0) {
        return AP4_SUCCESS;
    }

    /* see how much data we can write */
    free_space = m_Bits.GetBytesFree();
    if (*buffer_size > free_space) *buffer_size = free_space;

    /* write the data */
    return m_Bits.WriteBytes(buffer, *buffer_size); 
}

/*----------------------------------------------------------------------+
|    AP4_AdtsParser::FindHeader
+----------------------------------------------------------------------*/
AP4_Result
AP4_AdtsParser::FindHeader(AP4_UI08* header)
{
   int          available = m_Bits.GetBytesAvailable();
   unsigned int sync = 0;
   long         nbr_skipped_bytes = 0;

   /* look for the sync pattern */
   while (available-- >= AP4_ADTS_HEADER_SIZE) {
      sync = (m_Bits.ReadByte() << 8) | m_Bits.PeekByte();

      if ((sync & AP4_ADTS_SYNC_MASK) == AP4_ADTS_SYNC_PATTERN) {
         /* found a sync pattern, read the rest of the header */
         header[0] = (sync >> 8) & 0xFF;
         m_Bits.ReadBytes(&header[1], AP4_ADTS_HEADER_SIZE-1);

         return AP4_SUCCESS;
      } else {
         ++ nbr_skipped_bytes;
      }
   }

   return AP4_ERROR_NOT_ENOUGH_DATA;
}

/*----------------------------------------------------------------------+
|    AP4_AdtsParser::FindFrame
+----------------------------------------------------------------------*/
AP4_Result
AP4_AdtsParser::FindFrame(AP4_AacFrame& frame)
{
    unsigned int   available;
    unsigned char  raw_header[AP4_ADTS_HEADER_SIZE];
    AP4_Result     result;

    /* align to the start of the next byte */
    m_Bits.ByteAlign();
    
    /* find a frame header */
    result = FindHeader(raw_header);
    if (AP4_FAILED(result)) return result;

    /* parse the header */
    AP4_AdtsHeader adts_header(raw_header);

    /* check the header */
    result = adts_header.Check();
    if (AP4_FAILED(result)) goto fail;
    
    /* check that we have enough data to peek at the next header */
    available = AP4_ADTS_HEADER_SIZE + m_Bits.GetBytesAvailable();
    if (m_Bits.m_Flags & AP4_BITSTREAM_FLAG_EOS) {
        /* we're at the end of the stream, we only need the entire frame */
        if (available < adts_header.m_FrameLength) {
            return AP4_ERROR_NOT_ENOUGH_DATA;
        } 
    } else {
        /* peek at the header of the next frame */
        unsigned char peek_raw_header[AP4_ADTS_HEADER_SIZE];

        if (available < adts_header.m_FrameLength+AP4_ADTS_HEADER_SIZE) {
            return AP4_ERROR_NOT_ENOUGH_DATA;
        } 
        m_Bits.SkipBytes(adts_header.m_FrameLength-AP4_ADTS_HEADER_SIZE);
        m_Bits.PeekBytes(peek_raw_header, AP4_ADTS_HEADER_SIZE);
        m_Bits.SkipBytes(-((int)adts_header.m_FrameLength-AP4_ADTS_HEADER_SIZE));

        /* check the header */
        AP4_AdtsHeader peek_adts_header(peek_raw_header);
        result = peek_adts_header.Check();
        if (AP4_FAILED(result)) goto fail;

        /* check that the fixed part of this header is the same as the */
        /* fixed part of the previous header                           */
        if (!AP4_AdtsHeader::MatchFixed(peek_raw_header, raw_header)) {
            goto fail;
        }
    }

    /* fill in the frame info */
    frame.m_Info.m_Standard = (adts_header.m_Id == 1 ? 
                            AP4_AAC_STANDARD_MPEG2 :
                            AP4_AAC_STANDARD_MPEG4);
    switch (adts_header.m_ProfileObjectType) {
        case 0:
            frame.m_Info.m_Profile = AP4_AAC_PROFILE_MAIN;
            break;

        case 1:
            frame.m_Info.m_Profile = AP4_AAC_PROFILE_LC;
            break;

        case 2: 
            frame.m_Info.m_Profile = AP4_AAC_PROFILE_SSR;
            break;

        case 3:
            frame.m_Info.m_Profile = AP4_AAC_PROFILE_LTP;
    }
    frame.m_Info.m_FrameLength = adts_header.m_FrameLength-AP4_ADTS_HEADER_SIZE;
    frame.m_Info.m_ChannelConfiguration = adts_header.m_ChannelConfiguration;
    frame.m_Info.m_SamplingFrequencyIndex = adts_header.m_SamplingFrequencyIndex;
    frame.m_Info.m_SamplingFrequency = AP4_AdtsSamplingFrequencyTable[adts_header.m_SamplingFrequencyIndex];

    /* skip crc if present */
    if (adts_header.m_ProtectionAbsent == 0) {
        m_Bits.SkipBits(16);
    } 

    /* set the frame source */
    frame.m_Source = &m_Bits;

    return AP4_SUCCESS;

fail:
    /* skip the header and return (only skip the first byte in  */
    /* case this was a false header that hides one just after)  */
    //m_Bits.SkipBytes(-(AP4_ADTS_HEADER_SIZE-1));
    return AP4_ERROR_CORRUPTED_BITSTREAM;
}

/*----------------------------------------------------------------------+
|    AP4_AdtsParser::GetBytesFree
+----------------------------------------------------------------------*/
AP4_Size
AP4_AdtsParser::GetBytesFree()
{
	return (m_Bits.GetBytesFree());
}



/*----------------------------------------------------------------------+
|    AP4_AdtsParser::GetBytesAvailable
+----------------------------------------------------------------------*/
AP4_Size	
AP4_AdtsParser::GetBytesAvailable()
{
	return (m_Bits.GetBytesAvailable());
}



