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High-definition televisionHigh-definition television (HDTV) is video that has resolution substantially higher than that of traditional television systems (standard-definition television). HDTV hasone or two million pixels per frame, roughly five times that of SD. Early HDTV broadcasting used analog techniques, but today HDTV is digitally broadcast using video compression.

History ofhigh-definition televisionOn 2 November 1936 the BBC egan transmitting the world's first public regular high-definition service from the Victorian Alexandra Palace in north London. t therefore claims to bethe birthplace of television broadcasting as we know it today.
The term high definition once described a series of television systems originating from the late 1930s; however, these systems were onlyhigh definition when compared to earlier systems that were based on mechanical systems with as few as 30 lines of resolution.
The British high-definition TV service started trials in August 1936 anda regular service in November 1936 using both the (mechanical) Baird 240 line and (electronic) Marconi-EMI 05 line (377i) systems. The Baird system was discontinued in February 1937. In 1938 Francefollowed with their own 441-line system, variants of which were also used by a number of other countries. The US NTSCsystem joined in 1941. In 1949 France introduced an even higher-resolution standardat 819 lines (768i), a system that would be high definition even by today's standards, but it was monochrome only. All of these systems used interlacing and a 4:3 aspect ratio except the 240-linesystem which was progressive (actually described at the time by the technically correct term "sequential") and the 405-line system which started as 5:4 and later changed to 4:3. The 405-line system adoptedthe (at that time) revolutionary idea of interlaced scanning to overcome the flicker problem of the 240-line with its 25 Hz frame rate. The 240-line system could have doubled its frame rate but...