Ntsc-rs – open-source video emulation of analog TV and VHS artifacts

There actually were ones that did interactive chat, but that required a modem too.

For teletext it would display 40x25 text with eight colours (the colour control codes took up a character space) and simple block graphics, which was stored in the first 25 lines or so above the top of the screen.

In the UK, the BBC ran Ceefax and ITV ran Teletext, which you could access with a button on your TV remote. These days it's actually possible to recover them from VHS recordings with really careful analysis (the bandwidth wasn't really there for it to work with a naive data slicer). During the day BBC2 ran "Pages from Ceefax" with some library music behind, when it didn't have Test Card F up (making Carole Hersee the most broadcast face on British TV, probably even to this day).

The server is down, but I copied the C code to here

  #include 
  #include 
  #include 
  #include 
  
  #define TAU (6.283185307179586476925286766559005768394)
  
  static unsigned char head[16];
  static float fopt[127];
  static int iopt[127];
  static float*tab;
  static float*buf;
  static float y,i,q,v,phase;
  static int n,s,width;
  
  #define R(a) ((a)>=0?buf[a]:0.0)
  #define C(a) (tab[((a)+iopt['t']+(int)fopt['m'])%iopt['t']])
  
  int main(int argc,char**argv) {
    fopt['1']=0.966882;
    fopt['2']=0.623557;
    fopt['3']=-0.274788;
    fopt['4']=-0.635691;
    fopt['5']=-1.108545;
    fopt['6']=1.709007;
    iopt['y']=12;
    iopt['i']=iopt['q']=24;
    fopt['y']=12.0;
    fopt['i']=fopt['q']=24.0;
    fopt['l']=-11.0;
    fopt['h']=92.0;
    fopt['c']=0.009574;
    fopt['s']=0.8;
    fopt['a']=fopt['m']=fopt['p']=fopt['f']=0.0;
    fopt['t']=12.0;
    iopt['t']=12;
    iopt['v']=0;
    iopt['z']=0;
    fread(head,1,16,stdin);
    width=(head[8]>8); putchar(n);
      // Green
      v=fopt['s']*i/fopt['i'];
      n=(int)fmax(fmin(v*65535.0,65535.0),0.0);
      putchar(n>>8); putchar(n);
      // Blue
      v=fopt['s']*q/fopt['q'];
      n=(int)fmax(fmin(v*65535.0,65535.0),0.0);
      putchar(n>>8); putchar(n);
      // Alpha
      putchar(fgetc(stdin)); putchar(fgetc(stdin));
      if(!(s=(s+1)%width)) fopt['m']+=fopt['p'];
    } else for(;;) {
      if(!s) y=fopt['a'],i=q=0.0;
      n=fgetc(stdin);
      if(n==EOF) break;
      n=(n>8); putchar(n);
      // Green
      v=y*fopt['c']/fopt['y']+i*fopt['3']*fopt['c']*fopt['s']/fopt['i']+q*fopt['4']*fopt['c']*fopt['s']/fopt['q'];
      n=(int)fmax(fmin(v*65535.0,65535.0),0.0);
      putchar(n>>8); putchar(n);
      // Blue
      v=y*fopt['c']/fopt['y']+i*fopt['5']*fopt['c']*fopt['s']/fopt['i']+q*fopt['6']*fopt['c']*fopt['s']/fopt['q'];
      n=(int)fmax(fmin(v*65535.0,65535.0),0.0);
      putchar(n>>8); putchar(n);
      // Alpha
      putchar(fgetc(stdin)); putchar(fgetc(stdin));
      if(!(s=(s+1)%width)) fopt['m']+=fopt['p'];
    }
    return 0;
  }

NTSC's rate was 29.97 and its lesser line count made images seem blurry to those who were used to PAL and SECAM. Folks viewing PAL after NTSC felt that the flicker caused eye fatigue.

There's this: https://codeberg.org/fsphil/hacktv

It's not "VHS footage" though, but it can generate all kinds of analog video signals, some of which my decoder can decode.

It really was. I recently got on the VHS bandwagon and the audio feels much more richer to me than say a blu-ray or streaming copy. There's something about the imperfections that resonates with me.