Television Production

A TV program produced in one country can't automatically be viewed in many other countries without converting it to a different technical standard. These technical differences relate to both incompatibilities in equipment and in the approach to broadcasting the audio and video signals.

Some 14 different SDTV  (standard definition) broadcast TV standards have been used at different times throughout the world. They can be reduced to three primary groups:

• NTSC (National Television System Committee)
• SECAM (Sequential Color and Memory)
• PAL (Phase Alternating Line)

Within these there are two major differences:

• the total number of horizontal lines in the picture (525 or 625 for standard definition or SDTV) and 1,125 and 1,250 for high-definition TV (HDTV)
   
• whether the transmission rate is 25 or 30 frames (complete pictures) per-second
  
  

  Aspect Ratios 

  Although the number of scanning lines may have varied, until recently all television systems had a 4:3 aspect ratio. The aspect ratio is the width-height proportion of the picture.
  The 4:3 ratio (note red box in the photo on the right) was consistent with motion pictures that predated the wide screen aspect ratios used in CinemaScope, VistaVision, and Panavision. When the HDTV standard was introduced it also made use of this wider (generally, 16:9) aspect ratio.
  In the picture here, the wider area (just inside the blue borders) represents the 16:9 ratio used in HDTV. Compared to the 4:3 ratio, this aspect ratio conforms to the wider perspective of normal human vision.