Philips 14AA3322/40B Guía de instalación descargar pdf (Pagina 96)

Generation of a transport stream for DVB and realisation of a HF-modulated DVB-signal

96 | P a g e

Question24

Why are there green blocks on the snapshots?

Because we can’t decode whole IPB sequence. MPEG uses three different kinds of images to transmit

video: I (Intra), which contains a complete picture, P (Predictive) and B (Bidirectional). Both contain only

the difference between pictures and the “I” image. If we are not able to decode the “I” image, we will not

be able to see the whole picture. That is why the green blocks appear.

Question25

What kind of errors do we see?

We see continuity errors, CRC errors and TEI errors.

Figure: 2.11: Error chart

Question26

Explain the difference between CRC errors, TEI errors and continuity errors:

Continuity errors: Each TS carries out a counter from 0 to 15. If some numbers are missing, it means that

a packet has been lost, so it becomes an error.

CRC errors: Before transmitting them, a checksum of the data from every TS is done. We repeat the same

operation in reception; if the results do not match, it means that the data has been corrupted.

TEI Errors: The Reed-Solomon decoder in MPEG-2 can only correct 8 bytes for every transport stream, so

if a TS comes with more than 8 bytes wrong, the packed is flagged as Errored (changing a bit in the TS

header) and it must not be decoded by the MPEG decoder.

1 2 ... 91 92 93 94 95 96 97 98 99 100 101 ... 127 128

Sin comentarios

Philips 14AA3322/40B Guía de instalación Pagina 96