MetaPlaylist v0.1

Overview

The MetaPlaylist is a file allowing to define a content composed of multiple DASH or Smooth contents played one after another.

It allows advanced use cases for an extremely low cost for the server infrastructure, the main one being creating a linear (live) contents from multiple non-linear (VOD) ones, without touching the original contents.

You can also construct a new non-linear contents as a concatenation of multiple non-linear contents put one after the other. This method allows for example for a completely smooth streaming between multiple programs (e.g. when binge-watching a serie).

Differences with plain DASH contents

The same result could be approximated with some advanced DASH features, but the MetaPlaylist has several advantages. Some of them are:

  • it supports DASH and HSS contents (technically HLS would also be possible) without modifying the original MPD/Manifest nor segments.

  • the Manifest/MPD/Playlist corresponding to the original contents can be lazy-loaded (loaded only when the content will play).

    This is also possible in DASH with a feature called XLinks but it’s not always doable on the client-side, depending on the other elements present in that MPD.

    A MetaPlaylist file is much more strict in this regard.

    This is still a work-in-progress.

  • it’s a format especially intended to be a concatenation of multiple contents to be played on the web.

    As such, advanced features such as declaring segments before they should be played or avoiding many customers doing the same manifest request at the exact same time are much easier to implement.

  • this file rarely needs to be updated, improving the caching of this ressource.

  • its format is very simple and in JSON, which is easy to integrate with JavaScript codebases. The file can even be very easily generated directly on the client’s page. This paves the way for contents personalized to a single customer.

  • Digital right management is also much more flexible than with a DASH MPD. For example, different license servers for different contents could be integrated. This is still a work-in-progress.

  • the specification is simple, try to allow no interpretation and is strict on what is permitted.

  • All its features have been tested on web applications, meaning that you have the guarantee everything will work on most MSE-compatible browsers, even IE11.

Structure of a MetaPlaylist

A MetaPlaylist file is a simple JSON file.

To jump into it right away, let me introduce some examples.

For a VOD content:

{
  "type": "MPL",
  "version": "0.1",
  "contents": [
    {
      "url": "http://url.to.some/DASH/first_content.mpd",
      "startTime": 0,
      "endTime": 100.38,
      "transport": "dash"
    },
    {
      "url": "http://url.to.some/DASH/second_content.Manifest",
      "startTime": 100.38,
      "endTime": 372,
      "transport": "smooth"
    },
    {
      "url": "http://url.to.some/Smooth/third_content.mpd",
      "startTime": 372,
      "endTime": 450.787,
      "transport": "dash"
    }
  ]
}

For a live content:

{
  "type": "MPL",
  "version": "0.1",
  "dynamic": true,
  "pollInterval": 5,
  "contents": [
    {
      "url": "http://url.to.some/DASH/content.mpd",
      "startTime": 1545845950.176,
      "endTime": 1545845985.571,
      "transport": "dash"
    },
    {
      "url": "http://url.to.some/other/DASH/content.mpd",
      "startTime": 1545845985.571,
      "endTime": 1545845998.71,
      "transport": "dash"
    },
    {
      "url": "http://url.to.some/Smooth/content.Manifest",
      "startTime": 1545845998.71,
      "endTime": 1545845117,
      "transport": "smooth"
    }
  ]
}

You may already have a basic understanding of it how works. Let’s define nonetheless every property in that JSON file.

the header

What I call the “header” here is roughly all root properties but “contents”.

Here is an exhaustive list of what you should put there:

  • type (string): should always be equal to "MPL", for “MetaPlayList”.

    The purpose of this value is to facilitate the checks a player might want to perform to verify that it is handling a MetaPlaylist file. The end goal would be for example to improve error reporting for very frequent mistakes like not providing the URL of the right content.

  • version (string): version of the MetaPlaylist file. Separated in two parts by a point (‘.’).

    The first part indicates the major version. If its number is higher than what the client presently manage, the client should not try to read that file.

    The last part indicates the minor version: A new feature or fix have been added but its support is not needed by a client (a client written for the 1.0 version can be used even for the 1.99 version).

    Please note that there is an exception for 0.x versions, where each minor versions could have a breaking change (as it is in that case considered an experimental format).

    At the moment, there is only one version the version "0.1". Thus, this is what you have to set in your JSON if you integrate this specification.

  • dynamic (boolean|undefined): If true, the MetaPlaylist file is not finished, and might need to be updated. If false, the MetaPlaylist could still need to be updated but its current content indicates a finished content: A player should end when the end of the last content has been reached.

    This property is not mandatory and as such can be omitted. By default, it is considered as not dynamic (so false).

  • pollInterval (number|undefined): If not set or set to a negative number, the MetaPlaylist file does not need to be reloaded.

    If set to a positive number, this is the maximum interval in seconds at which the MetaPlaylist file should be fetched from the server (which means that the MetaPlaylist could be refreshed more often depending on the current conditions).

    This should only be defined for dynamic contents.

    This property is not mandatory and as such can be omitted. By default, it is equivalent to -1 (which means no reload).

The contents

The contents are all defined as a property called contents at the top level of our MetaPlaylist file.

It is an array of one or multiple objects (an empty contents array is not a valid MetaPlaylist file).

Each of its objects are linked to a single content, here are the exhaustive list of its properties:

  • url (string): the URL to the original DASH’s MPD or Smooth’s Manifest. For now, only a subset of such contents is supported, mainly:

    • DASH contents that have their MPD@type set to "static"
    • Smooth content that have their isLive attribute not set to true (Simply put, only on-demand contents are supported for the moment).

  • startTime (number): time, in seconds, at which the beginning of this content should be played. This will correspond to the start time of the first Period in DASH or the first Chunk defined for Smooth content.

  • endTime (number): time, in seconds, at which the content should end. It the original content is longer, it will be finished at that time instead. The original content should not be shorter.

  • transport (string): indicates the original streaming protocol. Can be either of those values for now:

    • "dash": the URL points to a DASH’s MPD
    • "smooth": the URL points to a Microsoft Smooth Streaming’s Manifest.
    • "metaplaylist": Yes, it is possible to put MetaPlaylist files inside other MetaPlaylist files!

All those contents should be contiguous (meaning that the endTime of one should be the same value than the startTime of the following one).

How to actually play a MetaPlaylist content

Importing the METAPLAYLIST feature

The "METAPLAYLIST" feature is not included in the default RxPlayer build.

To import it, you first need to rely on the “minimal” version of the RxPlayer (through the "rx-player/minimal" import), you will need to import the METAPLAYLIST experimental feature and every transport protocol you might want to use.

For example if you need to use MetaPlaylist with both Smooth and DASH contents, you have to import at least all three as such:

import RxPlayer from "rx-player/minimal";
import { METAPLAYLIST } from "rx-player/experimental/features";
import { DASH, SMOOTH } from "rx-player/features";

RxPlayer.addFeatures([METAPLAYLIST, DASH, SMOOTH]);

More information about the minimal version of the RxPlayer can be found in the minimal player documentation.

Loading a MetaPlaylist content

A MetaPlaylist content can simply be played by setting a "metaplaylist" transport in loadVideo:

player.loadVideo({
  url: "http://www.example.com/metaplaylist.json",
  transport: "metaplaylist",
});

If you declare locally your MetaPlaylist file and do not want to set a URL for it, you can serve directly the file through the use of a Manifest Loader:

player.loadVideo({
  transport: "metaplaylist",

  // Note: `_url` here will be `undefined`
  manifestLoader(_url, callbacks) {
    // where `myMetaPlaylistObject` is the MetaPlaylist in either Object or
    // String form
    callbacks.resolve({ data: myMetaPlaylistObject });
  },
});

More infos on the manifestLoader can be found here.

Defining an initial position for a dynamic MetaPlaylist

As already explained, a MetaPlaylist can either be dynamic or static.

For calculating the initial position of those contents, the RxPlayer will obey the same rules than for other contents.

As such, dynamic MetaPlaylist contents will by default start just before the end of the last defined content which might not be what you want.

In those cases, you can make usage of the serverSyncInfos transport options when calling loadVideo to indicate the current time and construct the MetaPlaylist by using unix time for each content’s startTime and endTime.

The serverSyncInfos option is explained in the loadVideo options documentation.

For example, if you trust the user’s system clock to indicate the current live time (in most cases this is risky however), you can use the Date.now() api:

const serverSyncInfos = {
  serverTimestamp: Date.now(),
  clientTime: performance.now(),
};

player.loadVideo({
  transport: "metaplaylist",
  url: "https://www.example.com/metaplaylist",
  serverSyncInfos,
});

MetaPlaylist v0.1

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