# Video.JS HLS Live

## Brightcove Service Differences: 
- Brightcove uses the Zencoder HLS Live API.
- Once ingest begins, approximately 50 seconds later the original manifest is available. 
- I have not seen any ability to enforce a sliding window, so I believe Brightcove Live HLS serves all available segments on a continuously growing manifest. 
- One minute after last disconnect from the ingest stream, the event is considered complete and the final manifest delivered. 
- The final manifest will be different in two distinct ways, it will include the `EXT-X-ENDLIST` tag notifying all connected clients that the live stream has concluded and is now VOD. It will also contain a custom `ZEN-TOTAL-DURATION`: tag with representing the total amount of recorded time in seconds.

## Akamai Service Differences:
- Akamai only serves HLS Live off of Akamai HD2 endpoints.
- These vary from their HDS counterparts by url syntax.
	- ```<host> /i/``` vs.``` <host> /z/``` for HDS
	- `master.m3u8` vs.`manifest.f4m` for HDS
- Their endpoints are difficult to arrange CORS configurations on.
- Akamai manifests span the gamut of known HLS tags, both supported and unsupported by our plugin.

## Once Service Differences:
- Once manifests tend to include the use of `EXT-X-DISCONTINUITY` tags which are unsupported to date. 
- Once streams so far tend to use a different encoding algorithm on their segments which sometime result in a range error during transmuxing.


# Live HLS Research
This document is a collection of notes on Live HLS implementations in the wild.

There are two varieties of Live HLS. In the first, playlists are
persistent and strictly appended to. In the alternative form, the
maximum number of segments in a playlist is relatively stable and an
old segment is removed every time a new segment becomes available.

On iOS devices, both stream types report a duration of `Infinity`. The
`currentTime` is equal to the amount of the stream that has been
played back on the device.

## Akamai HD2

## OnceLIVE
"Sliding window" live streams.

### Variant Playlists
Once variant playlists look like standard HLS variant playlists.

### Media Playlists
OnceLIVE uses "sliding window" manifests for live playback. The media
playlists do not have an `EXT-X-ENDLIST` and don't declare a
`EXT-X-PLAYLIST-TYPE`.  On first request, the stream media playlist
returned four segment URLs with a starting media sequence of one,
preceded by a `EXT-X-DISCONTINUITY` tag. As playback progressed, that
number grew to 13 segment URLs, at which point it stabilized. That
would equate to a steady-state 65 second window at 5 seconds per
segment.

OnceLive documentation is [available on the Unicorn Media
website](http://www.unicornmedia.com/documents/2013/02/oncelive_implementationguide.pdf).

Here's a script to quickly parse out segment URLs:

```shell
curl $ONCE_MEDIA_PLAYLIST | grep '^http'
```

An example media playlist might look something like this:
```m3u8
#EXTM3U
#EXT-X-TARGETDURATION:5
#EXT-X-MEDIA-SEQUENCE:3
#EXTINF:5,3
http://example.com/0/1/content.ts?visitguid=uuid&asseturl=http://once.example.com/asset.lrm&failoverurl=http://example.com/blank.jpg
#EXTINF:5,4
http://example.com/1/2/content.ts?visitguid=uuid&asseturl=http://once.example.com/asset.lrm&failoverurl=http://example.com/blank.jpg
#EXTINF:5,5
http://example.com/2/3/content.ts?visitguid=uuid&asseturl=http://once.example.com/asset.lrm&failoverurl=http://example.com/blank.jpg
#EXTINF:5,6
http://example.com/3/4/content.ts?visitguid=uuid&asseturl=http://once.example.com/asset.lrm&failoverurl=http://example.com/blank.jpg
```

## Zencoder Live