npm install ebml[EBML][EBML] stands for Extensible Binary Meta-Language and is somewhat of a
binary version of XML. It's used for container formats like [WebM][webm] or
[MKV][mkv].
This is for version 3.0.0 and up, which has undergone a massive rewrite and
now builds with [RollupJS][rollup].
Version 2.2.4 is the last version to have guaranteed legacy semantics.
Install via NPM or Yarn:
``bash`
npm install ebml --saveor
yarn add ebml
The Decoder() class is implemented as a [Node Transform stream][node-stream-transform].
As input it takes EBML. As output it emits a sequence of chunks: two-element
arrays looking like this example.
`js`
[ "tag",
{
name: "TimecodeScale",
type: "u",
value: 1000000
}
]
The first element of the array is a short text string. For tags containing
values, like this example, the string is 'tag'. ebml also has nesting tags.'start'
The opening of those tags has the string and the closing has the'end'
string . Integers stored in 6 bytes or less are represented as numbers,
and longer integers are represented as hexadecimal text strings.
The second element of the array is an object with these members, among others:
* name is the [Matroska][mkv] Element Name.type
* is the data type.u
* : unsigned integer. Some of these are UIDs, coded as 128-bit numbers.i
* : signed integer.f
* : IEEE-754 floating point number.s
* : printable ASCII text string.8
* : printable utf-8 Unicode text string.d
* : a 64-bit signed timestamp, in nanoseconds after (or before) 2001-01-01T00:00UTC.b
* binary data, otherwise uninterpreted.value
* is the value of the data in the element, represented as a number or a string.data
* is the binary data of the entire element stored in a [Uint8Array][MDN-Uint8Array].
Elements with the [Block][mkv-block] and [SimpleBlock][mkv-sblock] types
get special treatment. They have these additional members:
* payload is the coded information in the element, stored in a [Uint8Array][MDN-Uint8Array].track
* is an unsigned integer indicating the payload's track.keyframe
* is a Boolean value set to true if the payload starts an I frame (SimpleBlocks only).discardable
* is a Boolean value showing the value of the element's Discardable flag. (SimpleBlocks only).
And the value member shows the block's Timecode value.
This example reads a media file into memory and decodes it. The decoder
invokes its event for each Element.
`js
const fs = require('fs');
const { Decoder } = require('./lib/ebml.js');
const decoder = new Decoder();
decoder.on('data', chunk => console.log(chunk));
fs.readFile('media/test.webm', (err, data) => {
if (err) {
throw err;
}
decoder.write(data);
});
`
This example does the same thing, but by piping the file stream into the decoder (a Transform stream).
`js
const { Decoder } = require('./lib/ebml.js');
const ebmlDecoder = new Decoder();
const counts = {};
require('fs')
.createReadStream('media/test.webm')
.pipe(ebmlDecoder)
.on('data', chunk => {
const { name } = chunk[1];
if (!counts[name]) {
counts[name] = 0;
}
counts[name] += 1;
})
.on('finish', () => console.log(counts));
`
Parsing should work. If it doesn't, please create [an issue][new-issue].
d`-type elements (timestamps) are not yet decoded to Javascript timestamp
values.
Thanks to @chrisprice we got an encoder!
(in alphabetical order)
* Chris Price
* Davy Van Deursen
* Ed Markowski
* Jonathan Sifuentes
* Manuel Wiedenmann
* Mark Schmale
* Mathias Buus
* Max Ogden
* Oliver Jones
* Oliver Walzer
[EBML]: http://ebml.sourceforge.net/
[new-issue]: https://github.com/node-ebml/node-ebml/issues/new
[MDN-Uint8Array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
[node-stream-transform]: https://nodejs.org/api/stream.html#stream_class_stream_transform
[mkv]: http://www.matroska.org/technical/specs/index.html
[rollup]: https://rollupjs.org/
[mkv-block]: https://www.matroska.org/technical/specs/index.html#block_structure
[mkv-sblock]: https://www.matroska.org/technical/specs/index.html#simpleblock_structure
[webm]: https://www.webmproject.org/