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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>reveal.js - The HTML Presentation Framework</title>
<meta name="description" content="A framework for easily creating beautiful presentations using HTML">
<meta name="author" content="Hakim El Hattab">
<meta name="apple-mobile-web-app-capable" content="yes" />
<meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no, minimal-ui">
<link rel="stylesheet" href="reveal.js-3.1.0/css/reveal.css">
<link rel="stylesheet" href="reveal.js-3.1.0/css/theme/blood.css" id="theme">
<!-- Code syntax highlighting -->
<link rel="stylesheet" href="reveal.js-3.1.0/lib/css/zenburn.css">
<!-- Printing and PDF exports -->
<script>
var link = document.createElement( 'link' );
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = window.location.search.match( /print-pdf/gi ) ? 'css/print/pdf.css' : 'css/print/paper.css';
document.getElementsByTagName( 'head' )[0].appendChild( link );
</script>
<!--[if lt IE 9]>
<script src="lib/js/html5shiv.js"></script>
<![endif]-->
<style>
.red { color: red; }
.lime { color: lime; }
.orange { color: orange; }
</style>
</head>
<body>
<div class="reveal">
<!-- Any section element inside of this container is displayed as a slide -->
<div class="slides">
<section>
<h1>Let's Make a Netflix</h1>
<h3>An Intro to Streaming Media on the Web</h3>
<p>
<small><a href="https://nickdesaulniers.github.io/">Nick Desaulniers</a> / <a href="http://twitter.com/lostoracle">@LostOracle</a></small>
</p>
</section>
<section>
<h2>Topics</h2>
<p class="fragment">Terminology</p>
<p class="fragment">Transcoding</p>
<p class="fragment">Audio & Video tags</p>
<p class="fragment">MSE</p>
<p class="fragment">DASH</p>
</section>
<section>
<section>
<h2>Terminology</h2>
</section>
<section>
<h2>Pulse Coded Modulation</h2>
Audio PCM streams are made up of a sample rate: how frequently the
amplitude is measured (ex. 320 Mbps), and bit depth: how many
possible digital values can be represented by one sample.
</section>
<section>
<h2>Compression</h2>
The Digital to Audio Converter (DAC) on your computer's soundcard
expects PCM (HD Audio or AC'97), but PCM is large and therefore
expensive to store and transmit.
</section>
<section>
<h2>Lossy vs Lossless Compression</h2>
<p>
Lossless compression allows us to more efficiently represent the
same uncompressed data and also sounds fantastic on your expensive
audio equipment.
</p>
<p>
Lossy compression sacrifices fidelity for
size and allows you to store thousands of songs on your phone.
</p>
</section>
<section>
<h2>Lossy vs Lossless Compression</h2>
<p>Lossless to lossy is a one way conversion</p>
<p>You cannot get back fidelity once it's been thrown away</p>
<img src="enhance.png" alt="enhance"/>
</section>
<section>
<h2>Codecs</h2>
Codecs are how the media data is represented, or encoded. Some
codecs are lossy like MP3, some are lossless like FLAC. Most codecs
are encumbered by patents. :(
</section>
<section>
<h2>Containers</h2>
Containers such as WAV, MP4, and Ogg represent the meta-data of a
media file such as artist or duration, subtitles, etc. Containers,
in addition to their meta-data, will contain streams of audio or
video encoded via a specific codec.
</section>
<section>
<h2>File Extension</h2>
Sometimes used by OS to determine what program should open what file.
Unreliable; anyone can change the file extension of a given file, but
that does not change the encoding (how the bits are arranged) or the
container (how the meta-data and streams are packaged).
</section>
<section>
<h2>Playlists</h2>
Playlist files are used by media playing applications to play
subsequent mediums. Browsers do not understand playlist files, but
playlist files can easily be
<a href="https://github.com/nickdesaulniers/javascript-playlist-parser">parsed</a>
in JavaScript.
</section>
<section>
<h2>Protocol</h2>
How are the bits transferred from one machine to another? On the
Web, HTTP is the most familiar, but there are other protocols used
when streaming media such as RTSP and ICY.
</section>
<section>
<h2>Know Your Terms</h2>
Codecs, containers, file extensions, playlist files, and protocols
are not equivalent. Ex. Media A could be aac encoded, in an MP4
container, with a .m4a extension, listed in a m3u playlist file,
served over ICY.
</section>
<section>
<h2>Hardware Acceleration</h2>
Media can be decoded in software or in hardware. Application
Specific Integrated Circuits (ASICs) can be faster and more power
efficient than General Purpose Processors. Mobile friendly. They
can also be patent encumbered.
</section>
</section>
<section>
<section>
<h2>Transcoding</h2>
</section>
<section>
<h2>Why?</h2>
<ul>
<li>Not all browsers support all codecs.</li>
<li>A lossy to lossy conversion is preferable to asking the user to install
a different browser.</li>
<li>If storage is cheaper than bandwidth, also preferable.</li>
</ul>
</section>
<section>
<h2>FFmpeg</h2>
<p>Your free and Open Source transcoding swiss army knife.</p>
<pre>
<code>
$ ffmpeg -h full 2>/dev/null| wc -l
5424
</code>
</pre>
</section>
<section>
<h2>The Extreme Basics</h2>
<pre><code class="bash">
ffmpeg -i input.wav output.mp3
ffmpeg -i input.y4m -i input.wav output.webm
</code></pre>
</section>
<section>
<h2>Codec support</h2>
<p><code class="lime">ffmpeg -codecs</code> will tell you if you can decode from one codec and encode into another.</p>
<pre><code class="lasso">
$ ffmpeg -codecs
DEV.LS h264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 (decoders: h264 h264_vda ) (encoders: libx264 libx264rgb )
DEV.L. vp8 On2 VP8 (decoders: vp8 libvpx ) (encoders: libvpx )
DEV.L. vp9 Google VP9 (decoders: vp9 libvpx-vp9 ) (encoders: libvpx-vp9 )
DEA.L. mp3 MP3 (MPEG audio layer 3) (decoders: mp3 mp3float ) (encoders: libmp3lame )
DEA.L. opus Opus (Opus Interactive Audio Codec) (decoders: opus libopus ) (encoders: libopus )
</code></pre>
<p class="fragment">If you're missing an expected encoder/decoder, you probably need to install a shared library and rebuild/reinstall ffmpeg. Not fun.</p>
</section>
<section>
<h2>FFmpeg</h2>
<p><code class="lime">ffmpeg -i input.file</code> will tell you a lot about a file.</p>
<!-- idk what lasso is, highlight.js makes it look fun! -->
<pre><code class="lasso">
$ ffmpeg -i bunny.mp4
Duration: 00:01:00.10 ...
Stream #0:0(eng): Audio: aac ... 22050 Hz, stereo, ... 65 kb/s
Stream #0:1(eng): Video: h264 ... 640x360, 612 kb/s, 23.96 fps ...
</code></pre>
</section>
<section>
<h2>Multiplexing</h2>
<p>aka muxing</p>
<pre><code class="lasso">
$ ffmpeg -i bunny.mp4
Stream #0:0(eng): Audio: aac ... 22050 Hz, stereo, ... 65 kb/s
Stream #0:1(eng): Video: h264 ... 640x360, 612 kb/s, 23.96 fps ...
Stream #0:2(eng): Data: none (rtp / 0x20707472), 45 kb/s
Stream #0:3(eng): Data: none (rtp / 0x20707472), 5 kb/s
$ ffmpeg -i bunny.mp4 -map 0:0 -map 0:1 -c copy bunny_clean.mp4
$ ffmpeg -i bunny_clean.mp4
Stream #0:0(eng): Audio: aac ... 22050 Hz, stereo, ... 65 kb/s
Stream #0:1(eng): Video: h264 ... 640x360, 612 kb/s, 23.96 fps ...
</code></pre>
</section>
</section>
<section>
<section>
<h2>Audio & Video Tags</h2>
</section>
<section>
<h2>AudioStream</h2>
<p><a href="https://github.com/nickdesaulniers/audiostream">A long time ago, I wanted to build iTunes in the browser.</a></p>
<img src="audiostream2.png" alt="audio stream application"/>
</section>
<section>
<h2>AudioStream</h2>
<img src="audiostream-arch.png" alt="Diagram of the architecture of audiostream"/>
</section>
<section>
<h2>Byte Range Requests</h2>
<p>A browser will make Byte Range Requests on behalf of a media element to
buffer content.</p>
<small>
<p>Request Headers:</p>
<ul>
<li>Range: bytes=0-</li>
</ul>
<p>Response Headers:</p>
<ul>
<li>Content-Length: 1024</li>
<li>Content-Range: 0-1023:4096</li>
</ul>
</small>
</section>
<section>
<h2>What if we want finer grain control over loading assets?</h2>
<p class="fragment">Why?</p>
<p class="fragment">Video is easily an order of magnitude larger in file size than audio.</p>
<p class="fragment">Waste of bandwidth if user downloads entire file, but watches only a part.</p>
</section>
<section>
<h2>Binary Data</h2>
<pre><code class="javascript">
var xhr = new XMLHttpRequest;
xhr.open('GET', 'song.mp3');
xhr.responseType = 'arraybuffer';
xhr.onload = function () {
var audio = new Audio;
audio.src = URL.createObjectURL(new Blob([xhr.response], {
type: 'audio/mpeg' }));
audio.oncanplaythrough = audio.play.bind(audio);
};
xhr.send();
</code></pre>
<p class="fragment">plus byte range requests?</p>
</section>
<section>
<h2>Binary data + byte range requests</h2>
<p>
Audio tags don't let us combine arraybuffers, they require one
contiguous arraybuffer. Web Audio API can help here.
</p>
<p class="fragment">But...</p>
<p class="fragment">
Results in audible clicks between segments. Finding the proper range
to segment by is very difficult. Web Audio API does not help here.
</p>
</section>
</section>
<section>
<section>
<h2>MSE</h2>
</section>
<section>
<h2>Browser Support</h2>
<small>MediaSource.isTypeSupported()</small>
<small>
<a href="http://www.w3.org/TR/media-source/byte-stream-format-registry.html">MSE Byte Stream Format Registry</a>,
</small>
<small>
<a href="http://www.leanbackplayer.com/test/h5mt.html">Notes</a>
</small>
<table style="transform: scale(0.75) translateX(-6em);">
<thead>
<tr>
<th>Browser</th>
<th>video/mp4</th>
<th>video/webm</th>
<th>video/mp2t</th>
<th>audio/mpeg</th>
<th>audio/aac</th>
</tr>
</thead>
<tbody>
<tr>
<td>Chrome<small style="vertical-align: baseline;">45</small></td>
<td class="lime">✓</td>
<td class="lime">✓*</td>
<td class="red">✗</td>
<td class="lime">✓</td>
<td class="lime">✓</td>
</tr>
<tr>
<td>Firefox <small style="vertical-align: baseline;">38</small></td>
<td class="lime">✓**</td>
<td class="red">✗</td>
<td class="red">✗</td>
<td class="red">✗</td>
<td class="red">✗</td>
</tr>
<tr>
<td>IE <small style="vertical-align: baseline;">11</style></td>
<td class="lime">✓</td>
<td class="red">✗</td>
<td class="lime">✓</td>
<td class="red">✗</td>
<td class="lime">✓</td>
</tr>
<tr>
<td>Opera <small style="vertical-align: baseline;">30</small></td>
<td class="lime">✓*</td>
<td class="lime">✓*</td>
<td class="red">✗</td>
<td class="red">✗</td>
<td class="red">✗</td>
</tr>
<tr>
<td>Safari <small style="vertical-align: baseline;">8</small></td>
<td class="lime">✓*</td>
<td class="red">✗</td>
<td class="red">✗</td>
<td class="red">✗</td>
<td class="red">✗</td>
</tr>
</tbody>
</table>
<p style="margin-top: -1em;">
<small>* Needs codec specified MediaSource.isTypeSupported('mime; codecs=""'); <a href="https://wiki.whatwg.org/wiki/Video_type_parameters#MPEG-4">List</a></small>
<small>** whitelisted to very few sites like YouTube, FF 38-41/42? Test in Nightly, media.mediasource.whitelist -> false in about:config</small>
</p>
</section>
<section>
<h2>A note about mp4</h2>
<p>mp4 needs to be "fragmented." <a href="http://www.w3.org/TR/media-source/isobmff-byte-stream-format.html#iso-init-segments">From ISO BMFF Byte Stream Format §3</a>:</p>
<blockquote>An ISO BMFF initialization segment is defined in this specification as a single File Type Box (<span class="lime">ftyp</span>) followed by a single Movie Header Box (<span class="lime">moov</span>).</blockquote>
<p class="fragment">wut?</p>
</section>
<section>
<h4>How to check if your mp4 is properly fragmented</h4>
<p>I highly recommend <a href="https://github.com/axiomatic-systems/Bento4">axiomatic-systems/Bento4</a> on GitHub.</p>
<pre>
$ ./mp4dump ~/Movies/devtools.mp4 | head
[<span class="red">ftyp</span>] size=8+24
...
[<span class="red">free</span>] size=8+0
[<span class="red">mdat</span>] size=8+85038690
[<span class="red">moov</span>] size=8+599967
...
</pre>
<p class="fragment">...<span class="lime">ftype</span> followed by a single <span class="lime">moov</span>...</p>
</section>
<section>
<h4>How to make your mp4 properly fragmented</h4>
<pre>
$ ./mp4fragment ~/Movies/devtools.mp4 devtools_fragmented.mp4
$ ./mp4dump devtools_fragmented.mp4 | head
[<span class="lime">ftyp</span>] size=8+28
...
[<span class="lime">moov</span>] size=8+1109
...
[<span class="orange">moof</span>] size=8+600
...
[<span class="orange">mdat</span>] size=8+138679
[<span class="orange">moof</span>] size=8+536
...
[<span class="orange">mdat</span>] size=8+24490
...
...
</pre>
<p>...<span class="lime">ftype</span> followed by a single <span class="lime">moov</span>...</p>
<p>You'll also notice multiple <span class="orange">moof</span>/<span class="orange">mdat</span> pairs.</p>
<p>When transcoding with ffmpeg, you'll want the flag: -movflags frag_keyframe+empty_moov</p>
</section>
<section>
<h2>HTMLMediaElement</h2>
<img src="audio_tag.png" alt="audio tag url relationship"/>
</section>
<section>
<h2>Media Source Extensions</h2>
<img src="mse_rel.png" alt="media source extension relationship"/>
</section>
<section>
<h2>MSE pseudocode</h2>
<pre><code class="coffeescript">
m = MediaSource
m.onsourceopen = () =>
s = m.addSourceBuffer 'codec'
s.onupdateend = () =>
if numChunks === totalChunks
m.endOfStream()
else
s.appendBuffer nextChunk
s.appendBuffer arrayBufferOfContent
video.src = URL.createObjectURL m
</code></pre>
</section>
<section>
<h2><a href="demo/bufferAll.html">Demo: buffer ASAP</a></h2>
</section>
<section>
<h2><a href="demo/bufferWhenNeeded.html">Demo: Buffer just in time</a></h2>
</section>
</section>
<section>
<section>
<h2>DASH</h2>
</section>
<section>
<h2>Adaptive Bitrate Streaming</h2>
<img src="abs_ema.png" alt="the gist of serving a segment of certain quality based on an exponential moving average of the measured bandwidth"/>
</section>
<section>
<h2>Asset pipeline</h2>
<img src="asset_pipeline.png" alt="How to generate all of the assets">
</section>
<section>
<h2>Browser caching</h2>
<p>Some browsers over-aggresively cache CORS related content.</p>
<p>In Safari, Develop > Empty Caches or Disable Caches</p>
<p>In Firefox 41, enable private browsing.</p>
</section>
<section>
<h2>DASH demo</h2>
<p>bugs</p>
<ul>
<li>
<a href="https://github.com/Dash-Industry-Forum/dash.js/issues/492">dash.js & Safari</a>
</li>
<li>
<a href="https://github.com/google/shaka-player/issues/101">shaka & Firefox</a>
</li>
</ul>
</section>
<section>
<h2>Live streaming</h2>
<a href="http://www.w3.org/TR/media-source/#widl-SourceBuffer-appendStream-void-ReadableStream-stream-unsigned-long-long-maxSize">SourceBuffer.prototype.appendStream</a>
</section>
</section>
</div>
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