/sdp-blob

Turn a WebRTC Offer/Answer into a compact blob/token

Primary LanguageJavaScript

sdp-blob

Turn a WebRTC Offer/Answer into a compact blob/token.

Only works with datachannel's.

37.42% reduction (average)

The goal of this library is to reduce the number of characters that represent enough data in the offer/answer to establish a WebRTC datachannel.

The reason I made this library is because I wanted a server-less WebRTC experience. This means you still need to transfer the offer/blob to a friend and have the friend send back the answer, but in as little characters as possible bringing it down to almost a small token.

To expand on that, I did not want to have to deal with a signaling server. Yes, the signaling server(means of which you transfer the offer/answer back and forth) is replaced by an IM client or email. Yes, it is more work on the user.

This library was developed when Chrome 38 was the latest version where you could see a 72% reduction by using SDP-Blob. At the moment it only reduces 30% for latest versions of Chrome and Firefox. (see table below)

Version: 1.0.0

Example blob:

Here is an example offer blob created by SDPBlob.assembleBlob(description). It can sent to someone else and parsed by SDPBlob.parseBlob(blob, type)

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

Usage:

CommonJS:

var sdpBlob = require('sdp-blob')

AMD:

require(['sdp-blob'], function(sdpBlob) {});

Browser standalone:

There is also a standalone build that can be directly used in a browser. sdp-blob-standalone.js

<script src="sdp-blob-standalone.js"></script>
<script>
// `SDPBlob` is a global to use now
</script>

API

SDPBlob.assembleBlob(description or options)

You can pass in just a sdp description string or an options object that has a description and encoding keys.

Using utf16 encoding instead of base64 will result in a much more reduced blob(~50% more) but produces some odd characters.

  • description: SDP string
  • encoding: Optional base64(default) or utf16

SDPBlob.parseBlob(options or blob, type)

Pass in the blob and type or an options object that has a blob and type keys

  • blob: A string provided from SDPBlob.assembleBlob()
  • type: A string. Most likely offer or answer
  • encoding: Optional base64(default) or utf16

Stats

These tables try to show you how SDPBlob compares to other methods for a given offer SDP description.

Browser % reduced SDPBlob.assembleBlob(...) DataBlob.assembleBlob(...) JSON.stringify(description)
Chrome 41.0.2229.1 33.97% reduced 552 594 836
Chrome 39.0.2171.65 34.45% reduced 548 594 836
Chrome 38.0.2125.122 72.97% reduced 552 594 2042
Firefox 35.0a2 24.30% reduced 788 1094 1041
Firefox 33.1.1 21.42% reduced 576 647 733

How the blob is made:

  • No need for audio media description. Chrome 38 seems to add it in when trying to create a data channel so we strip it out and regenerate a fake one on the client from the blob. This problem seems to be gone in Chrome Canary(40) so hopefully this part can get removed entirely.
  • Shorten all blob content keys before JSON.stringify. We restore the full key names on the client later on.
  • Compress with lz-string using the Base64 encoding for easy copy/paste-able characters.
  • Session ID does not matter so we just set it to a multi-digit random number
  • Reduce candidate priority number to single digit
  • Delete the candidate foundation and recreate it with a multi-digit random number
  • Remove colons from the fingerprint and convert from hex(base 16) to base 64. We can use a higher base but it results in more characters when compressed because of all of the specialty characters. 64 seems to be the sweet spot.

Building the standalone version

Here are multiple ways to build the browser standalone version youself.

Since we have a Gulp task to build the script you can simply run: gulp or npm run build-standalone

If you want to do it completely manually with browserify: browserify ./index.js --standalone SDPBlob > sdp-blob-standalone.js