Those are the days where "Good things always has to be Big", like the early version of a computer, which consumed a huge room for itself with those vacuum tubes and all. Then as the years passed, the size of quality goods reduced and became compact and the new age is "Small and efficient". Now PC's don't need air conditioning and you can take them with you anytime, anywhere.
This is the case with video formats as well. The high definition format or video evolved due to the need of our wanting more quality in what we see and thus the cameras and the optical lenses became more efficient and to a degree where common man cannot afford it. By the way, only better things become scarce and expensive to get. But even that is changing due to the advent of Handy cams, which gives high definition videos (1080p) at an affordable price.
To really understand the HD revolution, you need to know the encoding techniques that were/are used for non-HD videos. They are,
1.xvid (avi is the container)
2.divx (avi is the container)
3.mpeg-1 or 2 (mostly mpeg-2, because MPEG2 can be used up to 9.8 Mbit/sec video whereas MPEG1 can support only up to 1.856 MBit/sec video) (vob is the container).
The quality of the encoding format is of the descending order, while mpeg-2 being the least efficient (as it can only support resolutions up to 720x576), xvid is the successor of divx with improved efficiency.
But to fully utilize the enormous available memory space in a BD (Bluray Disc), an even better encoding technique was needed. The x264 (H264) encoding format was the solution, which can give similar or better results for half the video bit rate need for a quality than an xvid encoded video.
THE ARIVAL OF DVD, HD DVD AND THEN BLURAY DISC:
In the year 1993, new formats were introduced for storing a large amount of data (high definition videos) on an optical storage disc.One was MultiMedia Compact Disc (MMCD) and the other was (Super Density) SD disc. Companies like PHILIPS AND SONY supported MMCD and companies like TOSHIBA, THOMSON, TIME WARNER, HITACHI, PIONEER, MITSUBISHI,etc., supported SD disc.. But later to avoid conflict on the disc format a common format called UDF (Universal Disk Format) was adapted with the name DVD.
By the time the DVDs’ fame had grown from leaps and bounds, so did the quest for better quality encoding. “Better” in a sense, efficient encoding with smaller video bit rate(which is nothing but compression). While the DVDs’ adapted mpeg encoding format, with restricted resolution (576), the other successive formats had the privilege to support HD resolution.
HD DVD and BLURAY DISC:
In 2006, a new format called Blu-ray Disc (BD), designed by Sony, Philips, and Panasonic, was released as the successor to DVDs’. Another format, HD DVD, competed unsuccessfully with this format in the format war of 2006–08. A dual layer Blu-ray Disc can store up to 50 GB of information and thus breaking the 8.5GB barrier of a dual layered DVD.(DVD-18 can support space up to 15.9GB[double sided dual layered]).
Hence a BD with 25 to 50GB space, it can give great quality videos with resolutions 1920x1080. But since the bluray players are expensive, DVD still is the highest selling disc format. A BD can be played by a PlayStation PS3, bluray players, XBOX360, WD TV HD player etc, But to enjoy the full quality of a BD movie, HDTV is needed. And thus started another evolutionary improvement among TVs’. Then came the LCDs’ and the Plasmas’.