Self-hosted videos with HLS

Vincent Bernat

Note

This article was first published on Exoscale blog with some minor modifications.

Hosting videos on YouTube is convenient for several reasons: pretty good player, free bandwidth, mobile-friendly, network effect and, at your discretion, no ads.1 On the other hand, this is one of the less privacy-friendly solution. Most other providers share the same characteristics—except the ability to disable ads for free.

With the <video> tag, self-hosting a video is simple:2

<video controls>
  <source src="../videos/big_buck_bunny.webm" type="video/webm">
  <source src="../videos/big_buck_bunny.mp4" type="video/mp4">
</video>

However, while it is possible to provide a different videos depending on the screen width, adapting the video to the available bandwidth is trickier. There are two solutions:

They are both adaptive bitrate streaming protocols: the video is sliced in small segments and made available at a variety of different bitrates. Depending on current network conditions, the player automatically selects the appropriate bitrate to download the next segment.

HLS was initially implemented by Apple but is now also supported natively by Microsoft Edge and Chrome on Android. hls.js is a JavaScript library bringing HLS support to other browsers. MPEG-DASH is technically superior (codec-agnostic) but only works through a JavaScript library, like dash.js. In both cases, support of the Media Source Extensions is needed when native support is absent. Safari on iOS doesn’t have this feature and cannot use MPEG-DASH. Consequently, the most compatible solution is currently HLS.

Encoding⚓︎

To serve HLS videos, you need three kinds of files:

  • the media segments (encoded with different bitrates/resolutions),
  • a media playlist for each variant, listing the media segments, and
  • a master playlist, listing the media playlists.

Media segments can come in two formats:

  • MPEG-2 Transport Streams (TS), or
  • Fragmented MP4.

Fragmented MP4 media segments are supported since iOS 10. They are a bit more efficient and can be reused to serve the same content as MPEG-DASH (only the playlists are different). Also, they can be served from the same file with range requests. However, if you want to target older versions of iOS, you need to stick with MPEG-2 TS.3

FFmpeg is able to convert a video to media segments and generate the associated media playlists. Peer5’s documentation explains the suitable commands. I have put together an handy (Python 3.6) script, video2hls, stitching together all the steps. After executing it on your target video, you get a directory containing:

  • media segments for each resolution (1080p_1_001.ts, 720p_2_001.ts, …)
  • media playlists for each resolution (1080p_1.m3u8, 720p_2.m3u8, …)
  • master playlist (index.m3u8)
  • progressive (streamable) MP4 version of your video (progressive.mp4)
  • poster (poster.jpg)

The script accepts a lot of options for customization. Use the --help flag to discover them. Run it with --debug to get the ffmpeg commands executed with an explanation for each flag. For example, the poster is built with this command:

ffmpeg \
  `# seek to the given position (5%)` \
   -ss 4 \
  `# load input file` \
   -i ../2018-self-hosted-videos.mp4 \
  `# take only one frame` \
   -frames:v 1 \
  `# filter to select an I-frame and scale` \
   -vf 'select=eq(pict_type\,I),scale=1280:720' \
  `# request a JPEG quality ~ 10` \
   -qscale:v 28 \
  `# output file` \
   poster.jpg

Serving⚓︎

So, we got a bunch of static files we can upload anywhere. Yet two details are important:

  • When serving from another domain, CORS needs to be configured to allow GET requests. Adding Access-Control-Allow-Origin: * to response headers is enough.4
  • Some clients may be picky about the MIME types. Ensure files are served with the ones in the table below.
Kind Extension MIME type
Playlists .m3u8 application/vnd.apple.mpegurl
MPEG2-TS segments .ts video/mp2t
fMP4 segments .mp4 video/mp4
Progressive MP4 .mp4 video/mp4
Poster .jpg image/jpeg

Let’s host our files on Exoscale’s Object Storage which is compatible with S3 and located in Switzerland. As an example, the Caminandes 3: Llamigos video is about 213 MiB (five sizes for HLS and one progressive MP4). It would cost us less than 0.01 € per month for storage and 1.42 € for bandwidth if 1000 people watch the 1080p version from beginning to end—unlikely.5

We use s3cmd to upload files. First, you need to recover your API credentials from the portal and put them in ~/.s3cfg:

[default]
host_base = sos-ch-dk-2.exo.io
host_bucket = %(bucket)s.sos-ch-dk-2.exo.io
access_key = EXO.....
secret_key = ....
use_https = True
bucket_location = ch-dk-2

The second step is to create a bucket:

$ s3cmd mb s3://hls-videos
Bucket 's3://hls-videos/' created

You need to configure the CORS policy for this bucket. First, define the policy in a cors.xml file (you may want to restrict the allowed origin):

<CORSConfiguration>
 <CORSRule>
   <AllowedOrigin>*</AllowedOrigin>
   <AllowedMethod>GET</AllowedMethod>
 </CORSRule>
</CORSConfiguration>

Then, apply it to the bucket:

$ s3cmd setcors cors.xml s3://hls-videos

The last step is to copy the static files. Playlists are served compressed to save a bit of bandwidth. For each video, inside the directory containing all the generated files, use the following command:

while read extension mime gz; do
  [ -z "$gz" ] || {
    # gzip compression (if not already done)
    for f in *.${extension}; do
      ! gunzip -t $f 2> /dev/null || continue
      gzip $f
      mv $f.gz $f
    done
  }
  s3cmd --no-preserve -F -P \
        ${gz:+--add-header=Content-Encoding:gzip} \
        --mime-type=${mime} \
        --encoding=UTF-8 \
        --exclude=* --include=*.${extension} \
        --delete-removed \
    sync . s3://hls-videos/video1/
done <<EOF
m3u8  application/vnd.apple.mpegurl true
jpg   image/jpeg
mp4   video/mp4
ts    video/mp2t
EOF

The files are now available at https://hls-videos.sos-ch-dk-2.exo.io/video1/.

HTML⚓︎

We can insert our video in a document with the following markup:

<video poster="https://hls-videos.sos-ch-dk-2.exo.io/video1/poster.jpg"
       controls preload="none">
  <source src="https://hls-videos.sos-ch-dk-2.exo.io/video1/index.m3u8"
          type="application/vnd.apple.mpegurl">
  <source src="https://hls-videos.sos-ch-dk-2.exo.io/video1/progressive.mp4"
          type='video/mp4; codecs="avc1.4d401f, mp4a.40.2"'>
</video>

Browsers with native support use the HLS version while others would fall back to the progressive MP4 version. However, with the help of hls.js, we can ensure most browsers benefit from the HLS version too:

<script src="https://cdn.jsdelivr.net/npm/hls.js@latest"></script>
<script>
    if(Hls.isSupported()) {
        var selector = "video source[type='application/vnd.apple.mpegurl']",
            videoSources = document.querySelectorAll(selector);
        videoSources.forEach(function(videoSource) {
            var m3u8 = videoSource.src,
                once = false;

            // Clone the video to remove any source
            var oldVideo = videoSource.parentNode,
                newVideo = oldVideo.cloneNode(false);

            // Replace video tag with our clone.
            oldVideo.parentNode.replaceChild(newVideo, oldVideo);

            // On play, initialize hls.js, once.
            newVideo.addEventListener('play',function() {
                if (once) return;
                once = true;

                var hls = new Hls({ capLevelToPlayerSize: true });
                hls.loadSource(m3u8);
                hls.attachMedia(newVideo);
                hls.on(Hls.Events.MANIFEST_PARSED, function() {
                    newVideo.play();
                });
            }, false);
        });
    }
</script>

Here is the result, featuring Caminandes 3: Llamigos, a video created by Pablo Vasquez, produced by the Blender Foundation and released under the Creative Commons Attribution 3.0 license:

Most JavaScript attributes, methods and events work just like with a plain <video> element. For example, you can seek to an arbitrary position, like 1:00 or 2:00—but you would need to enable JavaScript to test.

The player is different from one browser to another but provides the basic needs. You can upgrade to a more advanced player, like video.js or MediaElements.js. They also handle HLS videos through hls.js.

Hosting your videos on YouTube is not unavoidable: serving them yourself while offering quality delivery is technically affordable. If bandwidth requirements are modest and the network effect not important, self-hosting makes it possible to regain control of the published content and not to turn over readers to Google. In the same spirit, PeerTube offers a video sharing platform. Decentralized and federated, it relies on BitTorrent to reduce bandwidth requirements.

Addendum⚓︎

Preloading⚓︎

In the above example, preload="none" was used for two reasons:

  • Most readers won’t play the video as it is an addon to the main content. Therefore, bandwidth is not wasted by downloading a few segments of video, at the expense of slightly increased latency on play.
  • We do not want non-native HLS clients to start downloading the non-HLS version while hls.js is loading and taking over the video. This could also be done by declaring the progressive MP4 fallback from JavaScript, but this would make the video unplayable for users without JavaScript. If preloading is important, you can remove the preload attribute from JavaScript—and not wait for the play event to initialize hls.js.

CSP⚓︎

Setting up CSP correctly can be quite a pain. For browsers with native HLS support, you need the following policy, in addition to your existing policy:

  • image-src https://hls-videos.sos-ch-dk-2.exo.io for the posters,
  • media-src https://hls-videos.sos-ch-dk-2.exo.io for the playlists and media segments.

With hls.js, things are more complex. Ideally, the following policy should also be applied:

  • worker-src blob: for the transmuxing web worker,
  • media-src blob: for the transmuxed segments,
  • connect-src https://hls-videos.sos-ch-dk-2.exo.io to fetch playlists and media segments from JavaScript.

However, worker-src is quite recent. The expected fallbacks are child-src (deprecated), script-src (but not everywhere) and then default-src. Therefore, for broader compatibility, you also need to append blob: to default-src as well as to script-src and child-src if you already have them. Here is an example policy—assuming the original policy was just default-src 'self' and media, XHR and workers were not needed:

HTTP/1.0 200 OK
Content-Security-Policy: 
  default-src 'self' blob:;
  image-src 'self' https://hls-videos.sos-ch-dk-2.exo.io;
  media-src blob: https://hls-videos.sos-ch-dk-2.exo.io;
  connect-src https://hls-videos.sos-ch-dk-2.exo.io;
  worker-src blob:;

  1. YouTube gives you the choice to not display ads on your videos. In advanced settings, you can unselect “Allow advertisements to be displayed alongside my videos.” Alternatively, you can also monetize your videos. ↩︎

  2. Nowadays, everything supports MP4/H.264. It usually also brings hardware acceleration, which improves battery life on mobile devices. WebM/VP9 provides a better quality at the same bitrate. ↩︎

  3. You could generate both formats and use them as variants in the master playlist. However, a limitation in hls.js prevents this option. ↩︎

  4. Use https://example.org instead of the wildcard character to restrict access to your own domain. ↩︎

  5. There is no need to host those files behind a (costly) CDN. Latency doesn’t matter much as long as you can sustain the appropriate bandwidth. ↩︎


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