Kamaelia.Device.DVB.Parse.ParseProgramMapTable

• component ParseProgramMapTable

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

Parsing Program Map Tables in DVB streams

ParseProgramMapTable 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 PMT 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

The possible 'descriptor' fields that feature in the table are explained in the DVB SI specification:

• ETSI EN 300 468 "Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems" ETSI / EBU (DVB group)

See Kamaelia.Support.DVB.Descriptors for information on how they are parsed.

Example Usage

A simple pipeline to receive, parse and display a particular Program Map Table in a multiplex, carried in packets with packet id 4228:

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,
}

PMT_PID = 4228

Pipeline( DVB_Multiplex(FREQUENCY, [PMT_PID], feparams),
          DVB_Demuxer({ PMT_PID:["outbox"]}),
          ReassemblePSITables(),
          ParseProgramMapTable(),
          PrettifyProgramMapTable(),
          ConsoleEchoer(),
        ).run()

Behaviour

Send reconstructed PSI table 'sections' to the "inbox" inbox. When all sections of the table have arrived, ParseProgramMapTable 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, similar to this (the 'streams' list here is abridged for brevity):

{
    'table_id' : 2,
    'table_type' : 'PMT',
    'current'  : 1,
    'services' : {
        4228: { 'video_pid'   : 610,
                'audio_pid'   : 611,
                'descriptors' : [],
                'pcr_pid'     : 610,
                'streams'     : [
                    { 'pid'         : 610,
                      'type'        : 2,
                      'descriptors' : [
                          ( 82, { 'type' : 'stream_identifier', 'component_tag' : 1 } )
                      ]
                    },
                    { 'pid'         : 611,
                      'type'        : 3,
                      'descriptors' : [
                          ( 10, { 'type' : 'ISO_639', 'entries' : [ { 'audio_type': '', 'language_code': 'eng' } ] } ),
                          ( 82, { 'type' : 'stream_identifier', 'component_tag' : 2 } )
                      ]
                    },

                    .....

                    { 'pid'        : 1010,
                      'type'       : 11,
                      'descriptors': [
                          ( 82, { 'type' : 'stream_identifier', 'component_tag' : 112 } )
                      ]
                    }
                ]
            }
    }
}

This table contains information about one service (with service id 4228), and describes many streams in that service. ParseProgramMapTable has identified that packets with packet id 610 and 611 probably contain the primary video and audio making up this service.

This is part of an instantaneous snapshot of a PMT broadcast from Crystal Palace MUX 1 (505.8MHz) in the UK on 20th Dec 2006.

If this data is sent on through a PrettifyProgramMapTable component, then the equivalent output is a string containing the following (again, abridged here for brevity):

PMT received:
    Table ID           : 2
    Table is valid for : CURRENT (valid)
    Services:
        Service id : 4228
        Program Clock Reference in PID : 610
        Service Descriptors:
            <<NONE>>
        Streams in service:
            Type : 2
                PID  : 610
                Stream Descriptors:
                    Descriptor 0x52 : stream_identifier
                        component_tag : 1
            Type : 3
                PID  : 611
                Stream Descriptors:
                    Descriptor 0xa : ISO_639
                        entries : [{'audio_type': '', 'language_code': 'eng'}]
                    Descriptor 0x52 : stream_identifier
                        component_tag : 2

            .....

            Type : 11
                PID  : 1010
                Stream Descriptors:
                    Descriptor 0x52 : stream_identifier
                        component_tag : 112

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

See the "MPEG Systems" and "DVB SI" specifications for information on the purposes of the descriptor fields that appear in various parts of this table.

See Kamaelia.Support.DVB.Descriptors for information on how each is parsed.

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?

ParseProgramMapTable 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.ParseProgramMapTable.ParseProgramMapTable

class ParseProgramMapTable(Axon.Component.component)

ParseProgramMapTable() -> new ParseProgramMapTable 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 from a single PID containing PMT table sections

Outboxes

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

Methods defined here

main(self)

parseTable(self, table_id, current_next, sections)

shutdown(self)