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.
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.
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.
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.
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;
}
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;
}
See Table 2-27 - Conditional access section.
interface MpegTsCat implements MpegTsSection {
attribute MpegTsDescriptor[] descriptors;
}
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;
}
See Table 2-30 - Private Section
interface MpegTsPrivateSection implements MpegTsSection {
attribute boolean privateIndicator;
attribute MpegTsSyntaxSection? syntaxSection;
ArrayBuffer privateData;
}
See Table 2-30-1 - The Transport Stream Description Table
interface MpegTsDescriptionSection implements MpegTsSection {
attribute MpegTsDescriptor[] descriptors;
}
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_idis 0, 1, 2, or 3 (PAT, CAT, PMT, Description), throw aMissingSyntaxSectionErrorifsyntax_section_indicatoris not 1. - If
syntax_section_indicatoris 1, throw anInvalidCrcErrorif the CRC-32 of the buffer is not 0. - If the
table_idis 0, return anMpegTsPat. - If the
table_idis 1, return anMpegTsCat. - If the
table_idis 2, return anMpegTsPmt. - If the
table_idis 3, return anMpegTsDescriptionSection. - If the
table_idis >= 128, return anMpegTsPrivateSection. - 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().