MPEG-TS Sections in JavaScript

Author: Brendan Long b.long@cablelabs.com

CRC-32 code adapted from the output of Thomas Pircher's (MIT licensed) pycrc.

This library decodes MPEG-TS program-specific information into JSON. It's intended to be used with HTML5 DataCues, but will work in any case where you have an ArrayBuffer.

For additional information, you may want to consult the ISO 13818-1 spec.

Using this library

To use, copy mpegtssections.js into your application's script directory, then add something like this to the <head> of your HTML page(s):

<script src="your-script-directory/mpegtssections.js"></script>

You can then use MpegTs methods in your JavaScript code.

Testing

You can run the tests using Node.js:

cd ~/mpegtssection-js
npm install
npm test # runs unit tests
npm run-script hint # runs JSHint

See test/tests.js for the Nodeunit tests.

JSHint follows directives in the /*jslint ... */ block at the top of each JavaScript file.

API Documentation

Data Structures

The following uses Web IDL syntax to describe the resulting data structures. The attribute names are taken directly from the MPEG-TS spec (except changed to CamelCase to match JavaScript conventions). Data which isn't only needed for parsing or validation is validated, but not exposed.

Generic MPEG-TS Section

interface MpegTsSyntaxSection {
    attribute unsigned short tableIdExtension;
    attribute octet versionNumber;
    attribute boolean currentNextIndicator;
    attribute octet sectionNumber;
    attribute octet lastSectionNumber;
}

interface MpegTsSection {
    attribute octet tableId;
    attribute MpegTsSyntaxSection? syntaxSection;
}

interface MpegTsDescriptor {
    attribute octet tag;
    attribute ArrayBuffer data;
}

Program Association Section

See Table 2-25 - Program association section

interface MpegTsPatProgramInfo {
    attribute unsigned short programNumber;

    // this is the network_PID if programNumber == 0,
    // or the program_map_PID if programNumber != 0
    attribute unsigned short pid;
}

interface MpegTsPat implements MpegTsSection {
    attribute unsigned short transportStreamId;
    attribute MpegTsPatProgramInfo[] programInfo;
}

Conditional Access Table

See Table 2-27 - Conditional access section.

interface MpegTsCat implements MpegTsSection {
    attribute MpegTsDescriptor[] descriptors;
}

Program Map Table

See Table 2-28 - Transport Stream program map section.

interface MpegTsElementaryStream {
    attribute octet streamType;
    attribute unsigned short elementaryPID;
    attribute MpegTsDescriptor[] descriptors;
}

interface MpegTsPmt implements MpegTsSection {
    attribute unsigned short programNumber;
    attribute unsigned short? pcrPID; // 8191 maps to null
    attribute MpegTsDescriptor[] descriptors;
    attribute MpegTsElementaryStreamData[] streams;
}

Private Section

See Table 2-30 - Private Section

interface MpegTsPrivateSection implements MpegTsSection {
    attribute boolean privateIndicator;
    attribute MpegTsSyntaxSection? syntaxSection;
    ArrayBuffer privateData;
}

Transport Stream Description

See Table 2-30-1 - The Transport Stream Description Table

interface MpegTsDescriptionSection implements MpegTsSection {
    attribute MpegTsDescriptor[] descriptors;
}

Functions

String MpegTs.decodeSection(ArrayBuffer buf)

If buf is a PSI table (starting with the table_id), it will be decoded into the most appropriate type, using the following algorithm:

If there are any serious problems with the data (lengths are wrong), throw a BadSizeError.
If table_id is 0, 1, 2, or 3 (PAT, CAT, PMT, Description), throw a MissingSyntaxSectionError if syntax_section_indicator is not 1.
If syntax_section_indicator is 1, throw an InvalidCrcError if the CRC-32 of the buffer is not 0.
If the table_id is 0, return an MpegTsPat.
If the table_id is 1, return an MpegTsCat.
If the table_id is 2, return an MpegTsPmt.
If the table_id is 3, return an MpegTsDescriptionSection.
If the table_id is >= 128, return an MpegTsPrivateSection.
Return an MpegTsSection.

unsigned short MpegTs.calculateCrc32(ArrayBuffer buf)

Calculates the CRC32/MPEG-2 of the given data. If you want to calculate the CRC of just part of the buffer, use ArrayBuffer.slice(). For a valid MPEG-TS section with a syntax section, the CRC-32 of all of the data from the table_id to the CRC_32 should be 0. This check will be run automatically by decodeSection().

schellkenig / mpegtssections-js