ECC Constraint Length
The number of sectors that are interleaved to combat bursty error characteristics of discs. 16 sectors are interleaved in DVD. Interleaving takes advantage of typical disc defects such as scratch marks by spreading the error over a larger data area, thereby increasing the chance that the error correction codes can conceal the error.



Edge Enhancement
When films are transferred to video in preparation for DVD encoding, they are commonly run through digital processes that attempt to clean up the picture. These processes include noise reduction (DVNR) and image enhancement. Enhancement increases contrast (similar to the effect of the "sharpen" or "unsharp mask" filters in PhotoShop), but can tend to overdo areas of transition between light and dark or different colors, causing a "chiseled" look or a ringing effect like the haloes you see around street lights when driving in the rain. Video noise reduction is a good thing, when done well, since it can remove scratches, spots, and other defects from the original film. Enhancement, which is rarely done well, is a bad thing. The video may look sharper and clearer to the casual observer, but fine tonal details of the original picture are altered and lost.


Elementary Stream
The output of an MPEG video encoder is a video elementary stream and the output of an audio encoder is an audio elementary stream. Before being multiplexed video and audio elementary streams are packetized to form the Video PES and the Audio PES.

PES Packet structure
The packet length is variable:

Header
packet start-code prefix (3bytes)
stream identifier (1 byte)
PES packet length (2 bytes)
optional PES HEADER (variable length)
stuffing bytes (FF) (variable length)
PES packet data bytes

The PES packets are the input of Program Stream and Transport Stream.



Encoding
Encoding is the process of changing data from one form into another according to a set of rules specifiec by a codec. The data is usually a file containing audio, video or still image. Often the encoding is done to make a file compatible with specific hardware (such as a DVD Player) or to compress or reduce the space the data occupies.

Common video encoding methods are DivX, MPEG-1, MPEG-2 and MPEG-4. A common audio encoding method is MP3 although many others exist including MPEG1 audio, DTS, and Dolby Digital.



Entropy coding
In entropy coding, also called variable length coding or Huffmann coding, the more likely values are associated to shorter codewords, while less likely values are associated to longer codewords.
Consequently, known the statistics of the event to code, provided that such statistics are representative enough, it is possible to code such event with an average number of bits lower than in fixed length coding.
So a variable number of bits is produced in the time unity, but many applications (transmission usually) need Constant Bit Rate. In this case the decoder needs a buffer, where it stores the received bits at constant bit rate and from which it gets the bits to decode at variable bit rate. The encoder must have a similar buffer for transmission and must take into account the decoder buffer size and buffer fillness so that neither overflow nor underflow occur at the decoder buffer. This is the purpose of Annex C to Specification ISO/IEC 13818-2 entitled Video buffering verifier.
The tool available to control the bit-rate is the changing of the quantiser_scale, but the rate control algorithm isn't specified and it's a responsability of the encoder.

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