mpv/libmpdemux/mpeg_hdr.c

// based on libmpeg2/header.c by Aaron Holtzman <aholtzma@ess.engr.uvic.ca>

// #include <inttypes.h>
#include <stdio.h>

#include "config.h"
#include "mpeg_hdr.h"

static int frameratecode2framerate[16] = {
  0,
  // Official mpeg1/2 framerates: (1-8)
  24000*10000/1001, 24*10000,25*10000,
  30000*10000/1001, 30*10000,50*10000,
  60000*10000/1001, 60*10000,
  // Xing's 15fps: (9)
  15*10000,
  // libmpeg3's "Unofficial economy rates": (10-13)
  5*10000,10*10000,12*10000,15*10000,
  // some invalid ones: (14-15)
  0,0
};


int mp_header_process_sequence_header (mp_mpeg_header_t * picture, unsigned char * buffer)
{
    int width, height;

    if ((buffer[6] & 0x20) != 0x20){
	fprintf(stderr, "missing marker bit!\n");
	return 1;	/* missing marker_bit */
    }

    height = (buffer[0] << 16) | (buffer[1] << 8) | buffer[2];

    picture->display_picture_width = (height >> 12);
    picture->display_picture_height = (height & 0xfff);

    width = ((height >> 12) + 15) & ~15;
    height = ((height & 0xfff) + 15) & ~15;

    picture->aspect_ratio_information = buffer[3] >> 4;
    picture->frame_rate_code = buffer[3] & 15;
    picture->fps=frameratecode2framerate[picture->frame_rate_code];
    picture->bitrate = (buffer[4]<<10)|(buffer[5]<<2)|(buffer[6]>>6);
    picture->mpeg1 = 1;
    picture->picture_structure = 3; //FRAME_PICTURE;
    picture->display_time=100;
    return 0;
}

static int header_process_sequence_extension (mp_mpeg_header_t * picture,
					      unsigned char * buffer)
{
    /* check chroma format, size extensions, marker bit */
	    
    if ( ((buffer[1] & 0x06) == 0x00) ||
         ((buffer[1] & 0x01) != 0x00) || (buffer[2] & 0xe0) ||
         ((buffer[3] & 0x01) != 0x01) )
	return 1;

    picture->progressive_sequence = (buffer[1] >> 3) & 1;
    picture->mpeg1 = 0;
    return 0;
}

static int header_process_picture_coding_extension (mp_mpeg_header_t * picture, unsigned char * buffer)
{
    picture->picture_structure = buffer[2] & 3;
    picture->top_field_first = buffer[3] >> 7;
    picture->repeat_first_field = (buffer[3] >> 1) & 1;
    picture->progressive_frame = buffer[4] >> 7;

    // repeat_first implementation by A'rpi/ESP-team, based on libmpeg3:
    picture->display_time=100;
    if(picture->repeat_first_field){
        if(picture->progressive_sequence){
            if(picture->top_field_first)
                picture->display_time+=200;
            else
                picture->display_time+=100;
        } else
        if(picture->progressive_frame){
                picture->display_time+=50;
        }
    }
    //temopral hack. We calc time on every field, so if we have 2 fields
    // interlaced we'll end with double time for 1 frame
    if( picture->picture_structure!=3 ) picture->display_time/=2;
    return 0;
}

int mp_header_process_extension (mp_mpeg_header_t * picture, unsigned char * buffer)
{
    switch (buffer[0] & 0xf0) {
    case 0x10:	/* sequence extension */
	return header_process_sequence_extension (picture, buffer);
    case 0x80:	/* picture coding extension */
	return header_process_picture_coding_extension (picture, buffer);
    }
    return 0;
}


//MPEG4 HEADERS
static unsigned char getbits(unsigned char *buffer, unsigned int from, unsigned char len)
{
    unsigned int n;
    unsigned char m, u, l, y;
    
    n = from / 8;
    m = from % 8;
    u = 8 - m;
    l = (len > u ? len - u : 0);
    
    y = (buffer[n] << m);
    if(8 > len)
    	y  >>= (8-len);
    if(l)
    	y |= (buffer[n+1] >> (8-l));
	
    //fprintf(stderr, "GETBITS(%d -> %d): bytes=0x%x 0x%x, n=%d, m=%d, l=%d, u=%d, Y=%d\n", 
    //	from, (int) len, (int) buffer[n],(int) buffer[n+1], n, (int) m, (int) l, (int) u, (int) y);
    return  y;
}

static int read_timeinc(mp_mpeg_header_t * picture, unsigned char * buffer, int n)
{
    if(picture->timeinc_bits > 8) {
      picture->timeinc_unit = getbits(buffer, n, picture->timeinc_bits - 8) << 8;
      n += picture->timeinc_bits - 8;
      picture->timeinc_unit |= getbits(buffer, n, 8);
      n += 8;
    } else {
      picture->timeinc_unit = getbits(buffer, n, picture->timeinc_bits);
      n += picture->timeinc_bits;
    }
    //fprintf(stderr, "TIMEINC2: %d, bits: %d\n", picture->timeinc_unit, picture->timeinc_bits);
    return n;
}

int mp4_header_process_vol(mp_mpeg_header_t * picture, unsigned char * buffer)
{
    unsigned int n, aspect=0, aspectw=0, aspecth=0,  x=1, v;
    
    //begins with 0x0000012x
    picture->fps = 0;
    picture->timeinc_bits = picture->timeinc_resolution = picture->timeinc_unit = 0;
    n = 9;
    if(getbits(buffer, n, 1))
      n += 7;
    n++;
    aspect=getbits(buffer, n, 4);
    n += 4;
    if(aspect == 0x0f) {
      aspectw = getbits(buffer, n, 8);
      n += 8;
      aspecth = getbits(buffer, n, 8);
      n += 8;
    }
    
    if(getbits(buffer, n, 1)) {
      n += 4;
      if(getbits(buffer, n, 1))
        n += 79;
      n++;
    } else n++;
    
    n+=3;
    
    picture->timeinc_resolution = getbits(buffer, n, 8) << 8;
    n += 8;
    picture->timeinc_resolution |= getbits(buffer, n, 8);
    n += 8;
    
    picture->timeinc_bits = 0;
    v = picture->timeinc_resolution - 1;
    while(v && (x<16)) {
      v>>=1;
      picture->timeinc_bits++;
    }
    picture->timeinc_bits = (picture->timeinc_bits > 1 ? picture->timeinc_bits : 1);
    
    n++; //marker bit
    
    if(getbits(buffer, n, 1)) {	//fixed_vop_timeinc
      n++;
      n = read_timeinc(picture, buffer, n);
      
      if(picture->timeinc_unit)
        picture->fps = (picture->timeinc_resolution * 10000) / picture->timeinc_unit;
    }
    
    //fprintf(stderr, "ASPECT: %d, PARW=%d, PARH=%d, TIMEINCRESOLUTION: %d, FIXED_TIMEINC: %d (number of bits: %d), FPS: %u\n", 
    //	aspect, aspectw, aspecth, picture->timeinc_resolution, picture->timeinc_unit, picture->timeinc_bits, picture->fps);
    
    return 0;
}

int mp4_header_process_vop(mp_mpeg_header_t * picture, unsigned char * buffer)
{
  int n;
  n = 0;
  picture->picture_type = getbits(buffer, n, 2);
  n += 2;
  while(getbits(buffer, n, 1))
    n++;
  n++;
  getbits(buffer, n, 1);
  n++;
  n = read_timeinc(picture, buffer, n);
}