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7800 MultiFrame Manual
7880DEC-MP2HD-2 Dual HD MPEG-2 Decoder
4.2.1. P1 Necessary for Decoding
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TS_sync_loss: The most important function for the evaluation of data from the MPEG-2 TS is
the sync acquisition. The actual synchronization of the TS depends on the number of correct
sync bytes necessary for the device to synchronize; two or more consecutive corrupted sync
bytes indicate sync loss. After synchronization has been achieved the evaluation of the other
parameters is carried out.
•
Sync_byte_error: The indicator "Sync_byte_error" is set as soon as the correct sync byte
(0x47) does not appear after 188 or 204 bytes. This is fundamental because this structure is
used throughout the channel encoder and decoder chains for synchronization. It is also
important that every sync byte is checked for correctness since encoders do not necessarily
check the sync byte.
•
PAT_error: The Program Association Table (PAT), which only appears in PID 0x0000 packets,
tells the decoder what programs are in the TS and points to the Program Map Tables (PMT)
which in turn point to the component video, audio and data streams that make up the program.
If the PAT is missing then the decoder can do nothing, no program is decodable. Nothing other
than a PAT should be contained in a PID 0x0000.
•
Continuity_count_error: For this indicator three checks are combined. The preconditions
"Incorrect packet order" and "Lost packet" could cause problems for receivers that are not
equipped with additional buffer storage and intelligence. It is not necessary for the test
equipment to distinguish between these two preconditions as they are logically OR-ed, together
with the third precondition, "a packet occurs more than twice" into one indicator.
•
PMT_error: The Program Association Table (PAT) tells the decoder how many programs there
are in the stream and points to the PMTs that contain the information where the parts for any
given event can be found. Parts in this context are the video stream (normally one), the audio
streams and the data stream (e.g. Teletext). Without a PMT the corresponding program is not
decodable.
•
PID_error: It is checked whether there exists a data stream for each PID that occurs. This error
often occurs where TS are multiplexed, or demultiplexed and again remultiplexed.
4.2.2. P2 Recommended
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Transport_error: The primary Transport_error indicator is Boolean which counts the erroneous
TS packets. This counter is intended for statistical evaluation of the errors. If an error occurs, no
further error indication should be derived from the erroneous packet.
•
CRC_error: The CRC check for the CAT, PAT, PMT, NIT, EIT, BAT, SDT and TOT indicates
whether the content of the corresponding table is corrupted. In this case no further error
indication should be derived from the content of the corresponding table.
•
PCR_error: The PCRs are used to re-generate the local 27 MHz system clock. If the PCR
does not arrive with sufficient regularity then this clock may jitter or drift. The PCR discontinuity
of more than 100 ms occurring without specific indication or the time interval between two
consecutive PCR values is more than 40 ms.
7880DEC-MP2HD-2 - 22
Revision 1.0
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