CyTube Custom Content Metadata

Last Updated: 2017-08-08

Status: Experimental

Purpose

CyTube currently supports adding custom audio/video content by allowing the user to supply a direct URL to an audio/video file. The server uses ffprobe to probe the file for various metadata, including the codec/container format and the duration. This approach has a few disadvantages over the officially supported media providers, namely:

Since it accepts a single file, it is not possible to provide multiple source URLs with varying formats or bitrates to allow viewers to select the best source for their computer.
- It also means it is not possible to provide text tracks for subtitles or closed captioning, or to provide image URLs for thumbnails/previews.
Probing the file with ffprobe is slow, especially if the content is hosted in a far away network location, which at best is inconvenient and at worst results in timeouts and inability to add the content.
Parsing the ffprobe output is inexact, and may sometimes result in detecting the wrong format, or failing to detect the title.

This document specifies a new supported media provider which allows users to provide a JSON manifest specifying the metadata for custom content in a way that avoids the above issues and is more flexible for extension.

Manifest Format

To add custom content, the user provides a JSON object with the following keys:

title: A nonempty string specifying the title of the content. For legacy reasons, CyTube currently truncates this to 100 UTF-8 characters.
duration: A non-negative, finite number specifying the duration, in seconds, of the content. This is what the server will use for timing purposes. Decimals are allowed, but CyTube's timer truncates the value as an integer number of seconds, so including fractional seconds lends no advantage.
live: An optional boolean (default: false) indicating whether the content is live or pre-recorded. For live content, the duration is ignored, and the server won't advance the playlist automatically.
thumbnail: An optional string specifying a URL for a thumbnail image of the content. CyTube currently does not support displaying thumbnails in the playlist, but this functionality may be offered in the future.
sources: A nonempty list of playable sources for the content. The format is described below.
textTracks: An optional list of text tracks for subtitles or closed captioning. The format is described below.

Source Format

Each source entry is a JSON object with the following keys:

url: A valid URL that browsers can use to retrieve the content. The URL must resolve to a publicly-routed IP address, and must the https: scheme.
contentType: A string representing the MIME type of the content at url. A list of acceptable MIME types is provided below.
quality: A number representing the quality level of the source. The supported quality levels are 240, 360, 480, 540, 720, 1080, 1440, and 2160. This may be extended in the future.
bitrate: An optional number indicating the bitrate (in Kbps) of the content. It must be a positive, finite number if provided. The bitrate is not currently used by CyTube, but may be used by extensions or custom scripts to determine whether this source is feasible to play on the viewer's internet connection.

Acceptable MIME Types

The following MIME types are accepted for the contentType field:

video/mp4
video/webm
video/ogg
application/x-mpegURL (HLS streams)
- HLS is only supported for livestreams. Metadata with HLS sources but without live: true will be rejected.
~~rtmp/flv~~
- In light of Adobe phasing out support for Flash, and many browsers already dropping support, RTMP is not supported by this feature. RTMP streams are only supported through the existing rt: media type.
audio/aac
audio/ogg
audio/mpeg

Other audio or video formats, such as AVI, MKV, and FLAC, are not supported due to lack of common support across browsers for playing these formats. For more information, refer to MDN.

Text Track Format

Each text track entry is a JSON object with the following keys:

url: A valid URL that browsers can use to retrieve the track. The URL must resolve to a publicly-routed IP address, and must the https: scheme.
contentType: A string representing the MIME type of the track at url. The only currently supported MIME type is text/vtt.
name: A name for the text track. This is displayed in the menu for the viewer to select a text track.

Important note regarding text tracks and CORS:

By default, browsers block requests for WebVTT tracks hosted on different domains than the current page. In order for text tracks to work cross-origin, the Access-Control-Allow-Origin header needs to be set by the remote server when serving the VTT file. See MDN for more information about setting this header.

Example

{
  "title": "Test Video",
  "duration": 10,
  "live": false,
  "thumbnail": "https://example.com/thumb.jpg",
  "sources": [
    {
      "url": "https://example.com/video.mp4",
      "contentType": "video/mp4",
      "quality": 1080,
      "bitrate": 5000
    }
  ],
  "textTracks": [
    {
      "url": "https://example.com/subtitles.vtt",
      "contentType": "text/vtt",
      "name": "English Subtitles"
    }
  ]
}

Permissions

The permission node to allow users to add custom content is the same as the permission node for the existing raw file support. Custom content is considered as an extension of the existing feature.

Unsupported/Undefined Behavior

The behavior under any the following circumstances is not defined by this specification, and any technical support in these cases is voided. This list is non-exhaustive.

Source URLs or text track URLs are hosted on a third-party website that does not have knowledge of its content being played on CyTube.
The webserver hosting the source or text track URLs serves a different MIME type than the one specified in the manifest.
The webserver hosting the source or text track URLs serves a file that does not match the MIME type specified in the Content-Type HTTP header returned to the browser.
The manifest includes source URLs or text track URLs with expiration times, session IDs, etc. in the URL querystring.

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