Kamaelia.Device.DVB.Parse.ParseServiceDescriptionTable

Parsing Service Description Tables in DVB streams

ParseServiceDescriptionTable 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 SDT and details of the fields within in are defined in the DVB SI specification, including the possible 'descriptor' fields that feature in the table:

• 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 the Service Description Table applying to the transport stream (MUX) being received ("actual TS"):

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,
}

SID_Actual_PID = 0x11

Pipeline( DVB_Multiplex(FREQUENCY, [SID_Actual_PID], feparams),
          DVB_Demuxer({ SID_Actual_PID:["outbox"]}),
          ReassemblePSITables(),
          ParseServiceDescriptionTable_ActualTS(),
          PrettifyServiceDescriptionTable(),
          ConsoleEchoer(),
        ).run()

A simple pipeline to receive and parse the Service Description Table then convert it to a simple list mapping service names to service ids:

Pipeline( DVB_Multiplex(FREQUENCY, [SID_Actual_PID], feparams),
          DVB_Demuxer({ SID_Actual_PID:["outbox"]}),
          ReassemblePSITables(),
          ParseServiceDescriptionTable_ActualTS(),
          SDT_to_SimpleServiceList(),
          ConsoleEchoer(),
        ).run()

ParseServiceDescriptionTable

Behaviour

At initialisation, specify whether you want ParseServiceDescriptionTables to parse 'actual' or 'other' tables (or both). 'Actual' tables describe services within the actual transport stream the table is it. 'Other' tables describe services carried in other transport streams - ie. broadcast in a different MUX in the same network. For example:

ParseServiceDescriptionTable(acceptTables = {0x42:"ACTUAL",0x46:"OTHER"})

There are shorthands available for the various combinations:

ParseServiceDescriptionTable_ActualTS()
ParseServiceDescriptionTable_OtherTS()
ParseServiceDescriptionTable_ActualAndOtherTS():

Send reconstructed PSI table 'sections' to the "inbox" inbox. When all sections of the table have arrived, ParseServiceDescriptionTable 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):

{
    'actual_other'        : 'ACTUAL',
    'table_type'          : 'SDT',
    'current'             : 1,
    'original_network_id' : 9018,
    'table_id'            : 66,
    'services': {
        4228: { 'running_status'       : 4,
                'free_CA_mode'         : 0,
                'eit_present_following': 1,
                'eit_schedule'         : 2,
                'descriptors': [
                    ( 72, { 'type': 'service',
                            'service_name': 'BBC TWO',
                            'service_type': 'digital television service',
                            'service_provider_name': 'BBC'
                          } ),
                    (115, { 'type': 'UNKNOWN',
                            'contents': 'fp.bbc.co.uk'
                          } )
                ] },
        4164: { 'running_status'       : 4,
                'free_CA_mode'         : 0,
                'eit_present_following': 1,
                'eit_schedule'         : 2,
                'descriptors': [
                    ( 72, { 'type': 'service',
                            'service_name': 'BBC ONE',
                            'service_type': 'digital television service',
                            'service_provider_name': 'BBC'
                          } ),
                    (115, { 'type': 'UNKNOWN',
                            'contents': 'fp.bbc.co.uk'
                          } )
                ] },

        .....

        4671: { 'running_status': 4,
                'free_CA_mode'         : 0,
                'eit_present_following': 1,
                'eit_schedule'         : 2,
                'descriptors': [
                    ( 72, { 'type': 'service',
                            'service_name': 'CBBC Channel',
                            'service_type': 'digital television service',
                            'service_provider_name': 'BBC'
                          } ),
                    (115, { 'type': 'UNKNOWN',
                            'contents': 'fp.bbc.co.uk'
                          } )
                ] }
        },
    'transport_stream_id': 4100
}

This table contains information about the services within the transport stream. It lists the services (channels) including their names. types, and the fact that there is now & next data (eit_present_following) and Electronic Programme Guide (eit_schedule) data available for each of them.

This is part of an instantaneous snapshot of the SDT broadcast from Crystal Palace MUX 1 (505.8MHz) in the UK on 21th Dec 2006.

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

Table ID           : 66
Table is valid for : CURRENT (valid)
Actual or Other n/w: ACTUAL
Transport stream id: 4100
Original network id: 9018
Services:
    Service id : 4228
        EIT present_following? : YES
        EIT schedule?          : YES
        Running status         : 4 (RUNNING)
        Scrambled?             : NO
        Service descriptors:
            Descriptor 0x48 : service
                service_name : 'BBC TWO'
                service_provider_name : 'BBC'
                service_type : 'digital television service'
            Descriptor 0x73 : UNKNOWN
                contents : 'fp.bbc.co.uk'
    Service id : 4164
        EIT present_following? : YES
        EIT schedule?          : YES
        Running status         : 4 (RUNNING)
        Scrambled?             : NO
        Service descriptors:
            Descriptor 0x48 : service
                service_name : 'BBC ONE'
                service_provider_name : 'BBC'
                service_type : 'digital television service'
            Descriptor 0x73 : UNKNOWN
                contents : 'fp.bbc.co.uk'

    .....

    Service id : 4671
        EIT present_following? : YES
        EIT schedule?          : YES
        Running status         : 4 (RUNNING)
        Scrambled?             : NO
        Service descriptors:
            Descriptor 0x48 : service
                service_name : 'CBBC Channel'
                service_provider_name : 'BBC'
                service_type : 'digital television service'
            Descriptor 0x73 : UNKNOWN
                contents : 'fp.bbc.co.uk'

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

See the "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?

ParseServiceDescriptionTable 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.

SDT_to_SimpleServiceList

Behaviour

Send parsed service description tables to this component's "inbox" inbox and a dictionary mapping service names to service ids will be sent out the "outbox" outbox. For example:

{ 'BBCi'        : 4479,
  'BBC ONE'     : 4164,
  'BBC TWO'     : 4228,
  'CBBC Channel': 4671,
  'BBC NEWS 24' : 4415,
  'BBC THREE'   : 4351
}

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.

- acceptTables  - dict of (table_id,string_description) mappings for tables to be accepted (default={0x42:"ACTUAL",0x46:"OTHER"})