PES packet construction
A DVD/HD DVD PES packet contains 2 kB of user data such as video, audio and sub-picture information. The user data is preceded by a header and followed by a 4-byte error detection code (EDC) as illustrated in Figure 20.7 to form a packet, also known as a sector. However, before the header and the EDC bytes are added, the 2 kB user data bits are scrambled. Scrambling avoids long strings of zeros to ensure that energy is evenly spread.
The header consists of three sections: a 4-byte ID section (consisting of a 3-byte sector number and 2-bytes of error detection for the sector number) and 6-byte copy protection information.
As stated earlier, to improve error correction, BD format employs the MPEG-2 transport stream in which the PES packets are further divided into 188-Byte transport packets as is the case with digital television broadcasting.
Forward error correction—DVD/HD DVD
Digital signals, especially those with a high level of compressions, require an efficient error-correction capability. Apart from normal errors of prop- agation and processing, errors may occur as a result of dust or physical damage to the surface of the disc causing video or audio break-up or dis- ruption. To avoid such errors, powerful FEC techniques are employed which can correct a burst error length of approximately 2800 bytes, corresponding to a physical damage of up to 6.0 mm. More stringent error- correction methods are used for the BD formats because of BD’s higher sensitivity to scratches and fingerprints.
Data is structured into blocks of 32 kB (DVD/HD DVD) and 64 kB (DB) of user data arranged in rows and columns. Following row interleaving, error-correction rows and columns are added to form recording or physi- cal sectors (Figure 20.8).