Kamaelia.Device.DVB.Parse.ParseProgramAssociationTable

• component ParseProgramAssociationTable

• Parsing Program Association Tables in DVB streams
  • Example Usage
  • Behaviour
  • How does it work?

Parsing Program Association Tables in DVB streams

ParseProgramAssociationTable parses a reconstructed PSI table from a DVB MPEG Transport Stream, and outputs a dictionary containing the data in the table.

The purpose of the PAT and details of the fields within in are defined in the MPEG systems specification:

• ISO/IEC 13818-1 (aka "MPEG: Systems") "GENERIC CODING OF MOVING PICTURES AND ASSOCIATED AUDIO: SYSTEMS" ISO / Motion Picture Experts Group

Example Usage

A simple pipeline to receive, parse and display the Program Association Table in a multiplex:

FREQUENCY = 505.833330
feparams = {
    "inversion" : dvb3.frontend.INVERSION_AUTO,
    "constellation" : dvb3.frontend.QAM_16,
    "code_rate_HP" : dvb3.frontend.FEC_3_4,
    "code_rate_LP" : dvb3.frontend.FEC_3_4,
}

PAT_PID = 0x0

Pipeline( DVB_Multiplex(FREQUENCY, [PAT_PID], feparams),
          DVB_Demuxer({ PAT_PID:["outbox"]}),
          ReassemblePSITables(),
          ParseProgramAssociationTable(),
          PrettifyProgramAssociationTable(),
          ConsoleEchoer(),
        ).run()

Behaviour

Send reconstructed PSI table 'sections' to the "inbox" inbox. When all sections of the table have arrived, ParseProgramAssociationTable will parse the table and send it out of its "outbox" outbox.

If the table is unchanged since last time it was parsed, then it will not be sent out. Parsed tables are only sent out when they are new or have just changed.

The parsed table is sent out as a dictionary data structure, like this:

{
    'table_id'         : 0
    'table_type'       : 'PAT',
    'current'          : 1,
    'NIT_PID'          : 16,
    'transport_streams': { 4100: { 4228: 4228,
                                   4351: 4351,
                                   4479: 4479,
                                   4164: 4164,
                                   4415: 4415,
                                   4671: 4671
                                 }
                         },
}

This is an instantaneous snapshot of the PAT for Crystal Palace MUX 1 transmission (505.8MHz) in the UK on 20th Dec 2006. If this data is sent on through a PrettifyProgramAssociationTable component, then the equivalent output is a string containing this:

PAT received:
Table ID           : 0
Table is valid for : CURRENT (valid)
NIT is in PID      : 16
For transport stream id : 4100
    For service 4228 : PMT is in PID 4228
    For service 4351 : PMT is in PID 4351
    For service 4479 : PMT is in PID 4479
    For service 4164 : PMT is in PID 4164
    For service 4415 : PMT is in PID 4415
    For service 4671 : PMT is in PID 4671

ParseProgramAssociationTable can collect the sections of, and then parse, both 'current' and 'next' tables simultaneously.

If a shutdownMicroprocess or producerFinished message is received on the "control" inbox, then it will immediately be sent on out of the "signal" outbox and the component will then immediately terminate.

How does it work?

ParseProgramAssociationTable logs all the table sections it receives, until it determines it has the complete set; then it parses them.

If the version number field in any table section changes, then the log is cleared, and the component starts collecting the sections again from scratch.

---

Kamaelia.Device.DVB.Parse.ParseProgramAssociationTable.ParseProgramAssociationTable

class ParseProgramAssociationTable(Axon.Component.component)

ParseProgramAssociationTable() -> new ParseProgramAssociationTable component.

Send reconstructed PSI table sections to the "inbox" inbox. When a complete table is assembled and parsed, the result is sent out of the "outbox" outbox as a dictionary.

Doesn't emit anything again until the version number of the table changes.

Outputs both 'current' and 'next' tables.

Inboxes

• control : Shutdown signalling
• inbox : DVB PSI Packets containing PAT table sections

Outboxes

• outbox : Parsed PAT table (only when it changes)
• signal : Shutdown signalling

Methods defined here

main(self)

parseTable(self, table_id, current_next, sections)

shutdown(self)