4.1.0 • Public • Published

render-media travis npm downloads javascript style guide

Intelligently render media files in the browser

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Show the file in a the browser by appending it to the DOM. This is a powerful package that handles many file types like video (.mp4, .webm, .m4v, etc.), audio (.m4a, .mp3, .wav, etc.), images (.jpg, .gif, .png, etc.), and other file formats (.pdf, .md, .txt, etc.).

The file will be streamed into the page (if it's video or audio). Seeking the media element will request a different byte range from the incoming file-like object.

In some cases, video or audio files will not be streamable because they're not in a format that the browser can stream, so the file will be fully downloaded before being played. For other non-streamable file types like images and PDFs, the file will be downloaded then displayed.

This module is used by WebTorrent.


npm install render-media


var render = require('render-media')
var from = require('from2')
var img = new Buffer('some jpg image data')
var file = {
  name: 'cat.jpg',
  createReadStream: function (opts) {
    if (!opts) opts = {}
    return from([ img.slice(opts.start || 0, opts.end || (img.length - 1)) ])
render.append(file, 'body', function (err, elem) {
  if (err) return console.error(err.message)
  console.log(elem) // this is the newly created element with the media in it


render.append(file, rootElem, [opts], [function callback (err, elem) {}])

file is an object with a name (string, with file extension) and createReadStream method which provides the file data.

Here's an example file:

var file = {
  name: 'file.mp4'
  createReadStream: function (opts) {
    var start = opts.start
    var end = opts.end
    // Return a readable stream that provides the bytes between offsets "start"
    // and "end" inclusive. This works just like fs.createReadStream(opts) from
    // the node.js "fs" module.

An optional file.length property can also be set to specify the length of the file in bytes. This will ensure that render-media does not attempt to load large files (>200 MB by default) into memory, which it does in the "blob" strategy. (See discussion of strategies below.)

rootElem is a container element (CSS selector or reference to DOM node) that the content will be shown in. A new DOM node will be created for the content and appended to rootElem.

If provided, opts can contain the following options:

  • autoplay: Autoplay video/audio files (default: false)
  • muted: Mute video/audio files (default: false)
  • controls: Show video/audio player controls (default: true)
  • maxBlobLength: Files above this size will skip the "blob" strategy and fail (default: 200 * 1000 * 1000 bytes)

Note: Modern browsers tend to block media that autoplays with audio (here's the Chrome policy for instance) so if you set autoplay to true, it's a good idea to also set muted to true.

If provided, callback will be called once the file is visible to the user. callback is called with an Error (or null) and the new DOM node that is displaying the content.

render.render(file, elem, [opts], [function callback (err, elem) {}])

Like render.append but renders directly into given element (or CSS selector).

why does video/audio streaming not work on file X?

Streaming support depends on support for MediaSource API in the browser. All modern browsers have MediaSource support.

Many file types are supported (again, depending on browser support), but only .mp4, .m4v, and .m4a have full support, including seeking.

rendering strategies

For video and audio, render-media tries multiple methods of playing the file:

  • videostream -- best option, supports streaming with seeking, but only works with MP4-based files for now (uses MediaSource API)
  • mediasource -- supports more formats, supports streaming without seeking (uses MediaSource API)
  • Blob URL -- supports the most formats of all (anything the <video> tag supports from an http url), with seeking, but does not support streaming (entire file must be downloaded first)

The Blob URL strategy will not be attempted if the file is over opts.maxBlobLength (200 MB by default) since it requires the entire file to be downloaded before playback can start which gives the appearance of the <video> tag being stalled. If you increase the size, be sure to indicate loading progress to the user in the UI somehow.

For other media formats, like images, the file is just added to the DOM.

For text-based formats, like html files, pdfs, etc., the file is added to the DOM via a sandboxed <iframe> tag.


MIT. Copyright (c) Feross Aboukhadijeh.

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  • feross
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