SDP Compact


Shorten WebRTC Session Description Protocol (SDP) based on Unified Plan SDP

Why?

A WebRTC SDP can remove some of the attributes to compress/compact and share config on both the offer and answer sides.

Features

- Shorten WebRTC SDP.
- Options to fixed parameters for both the offer and answer side.
- Compress with zlib deflate.
- Bytes based allow choosing any encoding.

Tri It Online

Installation

npm install sdp-compact

Examples

``TypeScript
import * as spdCompact from "sdp-compact";

const sessDesc: RTCSessionDescriptionInit = {
type: "offer",
sdp: v=0\r\no=- 4109260023080860376 2 IN IP4 127.0.0.1\r\ns=-\r\nt=0 0\r\na=extmap-allow-mixed\r\na=msid-semantic: WMS\r\n,
};


const options: spdCompact.Options = { compress: true };
// When compress is enabled, sdp-compact use base64 encoding by default. You can switch to base92 for more compact size:
const options: spdCompact.Options = { compress: 'base92' };

// compact the RTCSessionDescriptionInit
const compactedSessDesc = spdCompact.compact(sessDesc, options);
const decompactedSessDesc = spdCompact.decompact(compactedSPD, options);

// compact only the SDP string, will return base64 encoded if compress is enabled.
const compactedSPD = spdCompact.compactSDP(sessDesc.sdp, options);
// for decompact need to specify if it's offer or answer because it's not include in SDP
const decompactedSPD = spdCompact.decompactSDP(compactedSPD, true, options);

// compact only the SDP string to bytes
const compactedSPDBytes = spdCompact.compactSDPBytes(sessDesc.sdp, options);
// decompact the compacted SDP bytes to decompacted string
const decompactedSPD = spdCompact.decompactSDPBytes(compactedSPDBytes, true, options);
`

Options

You can override the default options to suit your application's requirements, while still keeping the default values for any unspecified properties.

$3

`Typescript
const DefaultOptions: Options = {
compress: 'base64'
replaceFieldNames: true,
sdpVersion: 0,
sessionName: "-",
origin: {
username: "-",
sessionId: "4109260023080860376",
netType: "IN",
addrtype: "IP4",
unicastAddress: "127.0.0.1",
},
timing: "0 0",
extmapAllowMixed: true,
msidSemantic: "WMS",
mediaOptions: {
removeMediaID: true,
removeSetup: true,
replaceCandidateString: true,
replaceMediaString: true,
forceTrickle: true,
compressFingerprint: true,
compressConnection: true,
compressExtmap: true,
compressRtcpFb: true,
},
};
`

Here is an explanation of each option and its default value:

$3

Enables compression using zlib deflate, followed by base64/base92 encoding.

$3

Replaces field names using FieldReplaceMap and FieldReplaceMapReverse.

$3

The fixed SDP version (v=), which is usually 0 for now.

$3

The fixed session name (s=), which is usually "-".

$3

Fixed origin options (o=). This includes the following properties:

- username: Fixed username, can be "-" for an undefined user. (default: "-")
- sessionId: Fixed session ID, can be the same value on all peers. (default: "4109260023080860376")
- netType: Fixed network type, must be "IN" for the internet. (default: "IN")
- addrtype: Fixed address type, must be either "IP4" or "IP6". Usually, it will be "IP4". (default: "IP4")
- unicastAddress: Fixed unicast address, usually "127.0.0.1". (default: "127.0.0.1")

$3

The fixed timing (t=). It can be "0 0" for unbounded.

$3

Allows mixing attributes (a=extmap-allow-mixed), usually allowed by default.

$3

The fixed msid semantic (a=msid-semantic:). It should be "WMS" for WebRTC Media Stream.

$3

Customize media options. This includes the following properties:

- removeMediaID: Remove media ID (a=mid:) and group (a=group:) (a=group:BUNDLE) to use sequence medias instead. (default: true)
- removeSetup: Remove DTLS role (a=setup:). It will set to actpass for offer and active for answer. (default: true)
- replaceCandidateString: replaced string in ice candidate (a=candidate:) following CandidateReplaceList. (default: true)
- replaceMediaString: replace string in media (m=) following MediaReplaceList. (default: true)
- forceTrickle: force ice-options to trickle (a=ice-options:trickle). (default: true)
- compressFingerprint: compress fingerprint (a=fingerprint:). (default: true)
- compressConnection: compress media connection (c=). (default: true)
- compressExtmap: compress extmap URIs by replacing common URNs with short identifiers (a=extmap:). (default: true)
- compressRtcpFb`: compress RTCP feedback types by replacing common types with short identifiers (a=rtcp-fb:). (default: true)

WebRTC SDP Anatomy

You can read the WebRTC SDP Anatomy Here for how it's works.

Projects using SDP Compact

- Zero Share - A client-side secure P2P file sharing using WebRTC.