83 lines
2.5 KiB
C++
83 lines
2.5 KiB
C++
#include "mpeg.h"
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namespace Mpeg{
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MP2Info parseMP2Header(const std::string &hdr){return parseMP2Header(hdr.c_str());}
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MP2Info parseMP2Header(const char *hdr){
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MP2Info res;
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// mpeg version is on the bits 0x18 of header[1], but only 0x08 is important --> 0 is version 2,
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// 1 is version 1
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// leads to 2 - value == version, -1 to get the right index for the array
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int mpegVersion = 1 - ((hdr[1] >> 3) & 0x01);
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// samplerate is encoded in bits 0x0C of header[2];
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res.sampleRate = sampleRates[mpegVersion][((hdr[2] >> 2) & 0x03)] * 1000;
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res.channels = 2 - (hdr[3] >> 7);
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res.layer = 4 - ((hdr[1] >> 1) & 0x03);
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return res;
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}
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void MPEG2Info::clear(){
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width = 0;
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height = 0;
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fps = 0;
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tempSeq = 0;
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frameType = 0;
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isHeader = false;
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}
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MPEG2Info parseMPEG2Header(const std::string &hdr){return parseMPEG2Header(hdr.data());}
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MPEG2Info parseMPEG2Header(const char *hdr){
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MPEG2Info res;
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parseMPEG2Header(hdr, res);
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return res;
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}
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bool parseMPEG2Header(const char *hdr, MPEG2Info &mpInfo){
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// Check for start code
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if (hdr[0] != 0 || hdr[1] != 0 || hdr[2] != 1){return false;}
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if (hdr[3] == 0xB3){// Sequence header
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mpInfo.isHeader = true;
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mpInfo.width = (hdr[4] << 4) | ((hdr[5] >> 4) & 0x0F);
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mpInfo.height = ((hdr[5] & 0x0F) << 8) | hdr[6];
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mpInfo.fps = frameRate[hdr[7] & 0x0F];
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return true;
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}
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if (hdr[3] == 0x00){// Picture header
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mpInfo.tempSeq = ((uint16_t)hdr[4] << 2) | (hdr[5] >> 6);
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mpInfo.frameType = (hdr[5] & 0x38) >> 3;
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return true;
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}
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// Not parsed
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return false;
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}
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void parseMPEG2Headers(const char *hdr, uint32_t len, MPEG2Info &mpInfo){
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mpInfo.clear();
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const char *offset = hdr;
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char *maxData = (char *)hdr + len - 5;
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if (maxData - hdr > 250){maxData = (char *)hdr + 250;}
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while (offset < maxData){
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if (offset[2] > 1){
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// We have no zero in the third byte, so we need to skip at least 3 bytes forward
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offset += 3;
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continue;
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}
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if (!offset[2]){
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// We skip forward 1 or 2 bytes depending on contents of the second byte
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offset += (offset[1] ? 2 : 1);
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continue;
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}
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if (!offset[0] && !offset[1]){parseMPEG2Header(offset, mpInfo);}
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// We have no zero in the third byte, so we need to skip at least 3 bytes forward
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offset += 3;
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}
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}
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MPEG2Info parseMPEG2Headers(const char *hdr, uint32_t len){
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MPEG2Info res;
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parseMPEG2Headers(hdr, len, res);
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return res;
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}
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}// namespace Mpeg
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