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NALUnit.cpp
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NALUnit.cpp
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//
// NALUnit.cpp
//
// Implementation of Basic parsing of H.264 NAL Units
//
// Geraint Davies, March 2004
//
// Copyright (c) GDCL 2004-2008 http://www.gdcl.co.uk/license.htm
#include "NALUnit.h"
// --- core NAL Unit implementation ------------------------------
NALUnit::NALUnit()
: m_pStart(NULL),
m_cBytes(0)
{
}
bool
NALUnit::GetStartCode(const BYTE*& pBegin, const BYTE*& pStart, int& cRemain) {
// start code is any number of 00 followed by 00 00 01
// We need to record the first 00 in pBegin and the first byte
// following the startcode in pStart.
// if no start code is found, pStart and cRemain should be unchanged.
const BYTE* pThis = pStart;
int cBytes = cRemain;
pBegin = NULL;
while (cBytes>= 4) {
if (pThis[0] == 0) {
// remember first 00
if (pBegin == NULL) {
pBegin = pThis;
}
if ((pThis[1] == 0) && (pThis[2] == 1)) {
// point to type byte of NAL unit
pStart = pThis + 3;
cRemain = cBytes - 3;
return true;
}
}else {
pBegin = NULL;
}
cBytes--;
pThis++;
}
return false;
}
bool
NALUnit::Parse(const BYTE* pBuffer, int cSpace, int LengthSize, bool bEnd) {
// if we get the start code but not the whole
// NALU, we can return false but still have the length property valid
m_cBytes = 0;
ResetBitstream();
if (LengthSize > 0) {
m_pStartCodeStart = pBuffer;
if (LengthSize > cSpace) {
return false;
}
m_cBytes = 0;
for (int i = 0; i < LengthSize; i++) {
m_cBytes <<= 8;
m_cBytes += *pBuffer++;
}
if ((m_cBytes+LengthSize) <= cSpace) {
m_pStart = pBuffer;
return true;
}
}else {
// this is not length-delimited: we must look for start codes
const BYTE* pBegin;
if (GetStartCode(pBegin, pBuffer, cSpace)) {
m_pStart = pBuffer;
m_pStartCodeStart = pBegin;
// either we find another startcode, or we continue to the
// buffer end (if this is the last block of data)
if (GetStartCode(pBegin, pBuffer, cSpace)) {
m_cBytes = int(pBegin - m_pStart);
return true;
}else if (bEnd) {
// current element extends to end of buffer
m_cBytes = cSpace;
return true;
}
}
}
return false;
}
// bitwise access to data
void
NALUnit::ResetBitstream() {
m_idx = 0;
m_nBits = 0;
m_cZeros = 0;
}
void
NALUnit::Skip(int nBits) {
if (nBits < m_nBits) {
m_nBits -= nBits;
}else {
nBits -= m_nBits;
while (nBits >= 8) {
GetBYTE();
nBits -= 8;
}
if (nBits) {
m_byte = GetBYTE();
m_nBits = 8;
m_nBits -= nBits;
}
}
}
// get the next byte, removing emulation prevention bytes
BYTE
NALUnit::GetBYTE() {
if (m_idx >= m_cBytes) {
return 0;
}
BYTE b = m_pStart[m_idx++];
// to avoid start-code emulation, a byte 0x03 is inserted
// after any 00 00 pair. Discard that here.
if (b == 0) {
m_cZeros++;
if ((m_idx < m_cBytes) && (m_cZeros == 2) && (m_pStart[m_idx] == 0x03)) {
m_idx++;
m_cZeros=0;
}
}else {
m_cZeros = 0;
}
return b;
}
unsigned long
NALUnit::GetBit() {
if (m_nBits == 0) {
m_byte = GetBYTE();
m_nBits = 8;
}
m_nBits--;
return (m_byte >> m_nBits) & 0x1;
}
unsigned long
NALUnit::GetWord(int nBits) {
unsigned long u = 0;
while (nBits > 0) {
u <<= 1;
u |= GetBit();
nBits--;
}
return u;
}
unsigned long
NALUnit::GetUE() {
// Exp-Golomb entropy coding: leading zeros, then a one, then
// the data bits. The number of leading zeros is the number of
// data bits, counting up from that number of 1s as the base.
// That is, if you see
// 0001010
// You have three leading zeros, so there are three data bits (010)
// counting up from a base of 111: thus 111 + 010 = 1001 = 9
int cZeros = 0;
while (GetBit() == 0)
{
cZeros++;
}
return GetWord(cZeros) + ((1 << cZeros)-1);
}
long
NALUnit::GetSE() {
// same as UE but signed.
// basically the unsigned numbers are used as codes to indicate signed numbers in pairs
// in increasing value. Thus the encoded values
// 0, 1, 2, 3, 4
// mean
// 0, 1, -1, 2, -2 etc
unsigned long UE = GetUE();
bool bPositive = UE & 1;
long SE = (UE + 1) >> 1;
if (!bPositive)
{
SE = -SE;
}
return SE;
}
// --- sequence params parsing ---------------
SeqParamSet::SeqParamSet()
: m_cx(0),
m_cy(0),
m_FrameBits(0)
{
// SetRect(&m_rcFrame, 0, 0, 0, 0);
}
void
ScalingList(int size, NALUnit* pnalu) {
long lastScale = 8;
long nextScale = 8;
for (int j = 0 ; j < size; j++) {
if (nextScale != 0) {
long delta = pnalu->GetSE();
nextScale = (lastScale + delta + 256) %256;
}
int scaling_list_j = (nextScale == 0) ? lastScale : nextScale;
lastScale = scaling_list_j;
}
}
bool
SeqParamSet::Parse(NALUnit* pnalu) {
if (pnalu->Type() != NALUnit::NAL_Sequence_Params) {
return false;
}
// with the UE/SE type encoding, we must decode all the values
// to get through to the ones we want
pnalu->ResetBitstream();
pnalu->Skip(8); // type
m_Profile = pnalu->GetWord(8);
m_Compatibility = (BYTE) pnalu->GetWord(8);
m_Level = pnalu->GetWord(8);
/*int seq_param_id =*/ pnalu->GetUE();
if ((m_Profile == 100) || (m_Profile == 110) || (m_Profile == 122) || (m_Profile == 144)) {
int chroma_fmt = pnalu->GetUE();
if (chroma_fmt == 3) {
pnalu->Skip(1);
}
/* int bit_depth_luma_minus8 = */ pnalu->GetUE();
/* int bit_depth_chroma_minus8 = */ pnalu->GetUE();
pnalu->Skip(1);
int seq_scaling_matrix_present = pnalu->GetBit();
if (seq_scaling_matrix_present) {
for (int i = 0; i < 8; i++) {
if (pnalu->GetBit()) {
if (i < 6) {
ScalingList(16, pnalu);
}else {
ScalingList(64, pnalu);
}
}
}
}
}
int log2_frame_minus4 = pnalu->GetUE();
m_FrameBits = log2_frame_minus4 + 4;
int POCtype = pnalu->GetUE();
if (POCtype == 0)
{
/*int log2_poc_minus4 =*/ pnalu->GetUE();
} else if (POCtype == 1)
{
pnalu->Skip(1); // delta always zero
/*int nsp_offset =*/ pnalu->GetSE();
/*int nsp_top_to_bottom = */ pnalu->GetSE();
int num_ref_in_cycle = pnalu->GetUE();
for (int i = 0; i < num_ref_in_cycle; i++) {
/*int sf_offset =*/ pnalu->GetSE();
}
}
else if (POCtype != 2) {
return false;
}
// else for POCtype == 2, no additional data in stream
/*int num_ref_frames =*/ pnalu->GetUE();
/*int gaps_allowed =*/ pnalu->GetBit();
int mbs_width = pnalu->GetUE();
int mbs_height = pnalu->GetUE();
m_cx = (mbs_width+1) * 16;
m_cy = (mbs_height+1) * 16;
// smoke test validation of sps
if ((m_cx > 2000) || (m_cy > 2000))
{
return false;
}
// if this is false, then sizes are field sizes and need adjusting
m_bFrameOnly = pnalu->GetBit() ? true : false;
if (!m_bFrameOnly) {
pnalu->Skip(1); // adaptive frame/field
}
pnalu->Skip(1); // direct 8x8
#if 0
SetRect(&m_rcFrame, 0, 0, 0, 0);
bool bCrop = pnalu->GetBit() ? true : false;
if (bCrop) {
// get cropping rect
// store as exclusive, pixel parameters relative to frame
m_rcFrame.left = pnalu->GetUE() * 2;
m_rcFrame.right = pnalu->GetUE() * 2;
m_rcFrame.top = pnalu->GetUE() * 2;
m_rcFrame.bottom = pnalu->GetUE() * 2;
}
if (!IsRectEmpty(&m_rcFrame)) {
m_rcFrame.right = m_cx - m_rcFrame.right;
m_rcFrame.bottom = m_cy - m_rcFrame.bottom;
}
#endif
// adjust rect from 2x2 units to pixels
if (!m_bFrameOnly) {
// adjust heights from field to frame
m_cy *= 2;
#if 0
m_rcFrame.top *= 2;
m_rcFrame.bottom *= 2;
#endif
}
// .. rest are not interesting yet
m_nalu = *pnalu;
return true;
}
// --- slice header --------------------
bool
SliceHeader::Parse(NALUnit* pnalu) {
switch(pnalu->Type()) {
case NALUnit::NAL_IDR_Slice:
case NALUnit::NAL_Slice:
case NALUnit::NAL_PartitionA:
// all these begin with a slice header
break;
default:
return false;
}
// slice header has the 1-byte type, then one UE value,
// then the frame number.
pnalu->ResetBitstream();
pnalu->Skip(8); // NALU type
pnalu->GetUE(); // first mb in slice
pnalu->GetUE(); // slice type
pnalu->GetUE(); // pic param set id
m_framenum = pnalu->GetWord(m_nBitsFrame);
return true;
}
// --- SEI ----------------------
SEIMessage::SEIMessage(NALUnit* pnalu) {
m_pnalu = pnalu;
const BYTE* p = pnalu->Start();
p++; // nalu type byte
m_type = 0;
while (*p == 0xff) {
m_type += 255;
p++;
}
m_type += *p;
p++;
m_length = 0;
while (*p == 0xff) {
m_type += 255;
p++;
}
m_length += *p;
p++;
m_idxPayload = int(p - m_pnalu->Start());
}
avcCHeader::avcCHeader(const BYTE* header, int cBytes)
{
if (cBytes < 8) {
return;
}
const BYTE* pEnd = header + cBytes;
int cSeq = header[5] & 0x1f;
header += 6;
for (int i = 0; i < cSeq; i++) {
if ((header+2) > pEnd) {
return;
}
int cThis = (header[0] << 8) + header[1];
header += 2;
if ((header+cThis) > pEnd) {
return;
}
if (i == 0) {
NALUnit n(header, cThis);
m_sps = n;
}
header += cThis;
}
if ((header + 3) >= pEnd) {
return;
}
int cPPS = header[0];
if (cPPS > 0) {
int cThis = (header[1] << 8) + header[2];
header += 3;
NALUnit n(header, cThis);
m_pps = n;
}
}