ebml-decoder

ebml-decoder

Streaming EBML decoder.

npm install ebml-decoder

See the live demo.

Usage

The module exposes a decoder constructor which inherits from writable stream. An decoder instance emits element events whenever a EBML element is encountered in the input data. The actual element value can be retrieved using the decoder.decode([options], callback) method.

var fs = require('fs');
var decoder = require('ebml-decoder');

fs.createReadStream('movie.mkv')
  .pipe(decoder({ schema: matroska }))
  .on('element', function(element) {
    if(element.name === 'Duration') {
      this.decode(function(value) {
        console.log('Duration', value);
      });
    }
  });

The constructor accepts an EBML schema object as an option. The schema should be an array of element definitions.

[
  {
    id: '0x4489',
    name: 'Duration',
    type: 'float',
    path: '0*1(\Segment\Info\Duration)'
  }
]

The constructor accepts following options.

• schema: EBML schema as specified above.
• header: A boolean indicating if the default EBML header schema should be applied (default true).
• strict: A boolean indicating if warnings (such as unknown element IDs) should be treated as errors (default true).
• maxIDLength: The maximum number of bytes of an EBML element ID (default 4).
• maxSizeLength: The maximum number of bytes of an EBML element size (default 8).

If maxIDLength or maxSizeLength is not passed the decoder tries to read the values from the EBML header else the above default values are used.

The decode method should only be called after the element event has been emitted. The provided callback is called immediately with no value for master elements. It accepts following options.

• type: Overwrite the type specified in the element schema.