Table of Contents
Some options are available that can be used on a running live stream. Different players/devices may e.g. request a playlist with a different DVR or timeshift window.
All the features specified in Player URLs, Limiting bandwidth use example, Using dynamic track selection or Select variant stream that HLS clients should start playout with are also available for Live.
DVR window length¶
This feature gives you the ability to dynamically scale your DVR window when needed. The value overrides (and is capped by) the value specified on server manifest creation.
A HTTP Live Streaming playlist becomes very large when using a large DVR window. A typical use case is to use the default value for all streaming formats, and use a lower setting for HLS.
|dvr_window_length=30||No DVR / Pure LIVE|
|dvr_window_length=300||5 minutes DVR|
|dvr_window_length=600||10 minutes DVR|
Using time_shift you can offset the live point, meaning the player will not start at ‘now’ but behind the live point. The player will start playing from the archive at the number of seconds specified. Note the player isn’t aware of the time shift, so it cannot move forward in time.
This is useful when you are recording content in one timezone and your viewers are in a different timezone.
|time_shift=120||2 minutes time shift|
|time_shift=600||10 minutes time shift|
Similar to Using different manifests in VOD use cases, different manifests can be very useful for Live playout control.
The difficulty with Live is that the origin updates the server manifest when the encoder starts with the posted audio/video bitrates, so at a minimum these need to be copied.
However, when the bitrates the encoder sends are always the same, then
IsmProxyPass (HTTP Proxy) can be used to point to a location returning
the manifest to be used - which can contain a selection of the bitrates or extra
The setup uses two locations in the virtual host, one for the encoder
<Location /> UspHandleIsm on </Location>
and one for playout, with
<Directory "/var/www/live/proxy"> IsmProxyPass http://live.unified-streaming.com/smil.php/ </Directory>
This proxy location then could return a static smil file same as the Live ingest
for bitrates (the body part), but with different options in
Notably, HLS AES-128 protected playout is enforced by adding an HLS AES-128 key
(while the encoder posts in the clear). PHP could also be used, for instance
when parameters need to be injected.
<?php error_reporting(0); $path_prefix='/var/www/live'; $content_encryption_key="0E9269F650394530DFF0F7CCCEA77B89"; Header('Content-Type: text/xml'); echo "<?xml version=\"1.0\" encoding=\"utf-8\"?>" ?> <smil xmlns="http://www.w3.org/2001/SMIL20/Language"> <head> <meta name="clientManifestRelativePath" content="channel00.ismc" /> <meta name="creator" content="Unified Streaming Platform (USP)" /> <meta name="lookahead_fragments" content="2" /> <meta name="dvr_window_length" content="1800" /> <meta name="archive_segment_length" content="3600" /> <meta name="archiving" content="false" /> <meta name="restart_on_encoder_reconnect" content="true" /> <meta name="database_path" content="<?php echo $path_prefix ?>/channel00/channel00.db3" /> <meta name="iss_playout" content="false" /> <meta name="hls_playout" content="aes" /> <meta name="hds_playout" content="false" /> <meta name="mpd_playout" content="false" /> <paramGroup id="hls"> <meta name="key" content=":<?php echo $content_encryption_key ?>" /> <meta name="license_server_url" content="http://live.unified-streaming.com" /> </paramGroup> </head> <body> <switch> <audio src="file:///<?php echo $path_prefix ?>/channel00/oceans-64k.isma" systemBitrate="65000"> <param name="trackID" value="1" valueType="data" /> <param name="trackName" value="audio" valueType="data" /> <param name="SamplingRate" value="48000" valueType="data" /> <param name="Channels" value="2" valueType="data" /> <param name="BitsPerSample" value="16" valueType="data" /> <param name="PacketSize" value="4" valueType="data" /> <param name="AudioTag" value="255" valueType="data" /> <param name="FourCC" value="AACL" valueType="data" /> <param name="CodecPrivateData" value="1190" valueType="data" /> </audio> <video src="file:///<?php echo $path_prefix ?>/channel00/oceans-380k.ismv" systemBitrate="370000"> <param name="trackID" value="1" valueType="data" /> <param name="trackName" value="video" valueType="data" /> <param name="MaxWidth" value="384" valueType="data" /> <param name="MaxHeight" value="160" valueType="data" /> <param name="FourCC" value="AVC1" valueType="data" /> <param name="CodecPrivateData" value="000000016742C00D96640C0ADFF80C800C88800001F480005DC0078A15500000000168CE32C8" valueType="data" /> </video> </switch> </body> </smil>
It’s important to note that absolute paths need to be used for database and file locations. Without these the origin cannot find the db3 and ismv files used for ingest.
The player request (as defined in Player URLs) looks like this:
#!/bin/bash curl -v http://live.unified-streaming.com/proxy/channel00/channel00.isml/manifest
The Encoder URL on the other hand looks like this:
and uses the original location without
Care must be taken when setting up the publishing point: the location of the .db3 file has to be specified so both ingest and playout share the same database. The path to the .db3 file is specified like this:
#!/bin/bash mp4split --database_path=/var/www/live/channel00/channel00.db3 -o test.isml
Without database_path the origin will use the relative path, wrongly prepending the .db3 file with ‘smil.php’. The corresponding error will look like this:
FMP4_404 /smil.php/channel00/channel00.db3: unable to open database file (sqlite3_open_v2)
The above example uses a simple PHP script that returns a smil file, but other locations may be used for IsmProxyPass as well, for instance a CMS or other. Query parameters may be used to trigger selection of options or pass paths to .db3 and .ismv files.
By default the live presentation is made available and the player starts playback at the live edge together with a scrubbar that includes the full length of the DVR window.
But there may be use cases where you would not wish to provide the ability to scrub beyond the programme you are making available.
For example if you are providing an EPG (Electronic Programme Guide) and you are providing a way of entering ongoing programmes that haven’t finished yet.
The user may not have access to watch anything before or after this programme. For example the eight o’clock news is broadcast after the movie Guardians of the Galaxy and the user doesn’t have the access rights to scrub back before the news and watch it. The same goes for what is being broadcast afterwards, ideally you would like to restrict the end point of the manifest to the end point (in the future) of the news and nothing beyond that.
It is also a common feature of live EPGs that when you enter an ongoing programme you have the option of a ‘start over’ or ‘restart’ button, that jumps back to the beginning of the programme.
This feature also brings parity to the link structure you may already be using in a CMS to provide either a reverse EPG or yet to be archived clips in your offering.
By using the restart and catch-up options all the above functionality can be delivered simply and reliably using time stamps on the URL.
Scenarios and Manifest types:
- If you pass a start time, then the Origin returns a LIVE manifest, but with a specific DVR window that allows you to rewind to the beginning of the program.
- If you pass a start time and end time in the future, then the Origin returns a manifest that allows you to rewind to the beginning of the program, but automatically ends at the given end time.
- If you pass a start time and end time in the past, then the Origin returns a VOD manifest of the program.
Assuming the current time is 2015-07-28T20:22:00.000 (20:22 on the 28th of July)
|t=2015-07-28T20:00:00.000||Start at the beginning of the eight o’clock news.|
|t=2015-07-28T20:00:00.000-2015-07-28T20:30:00.000||The complete eight o’clock news program and the weather until it ends at 20:30.|
|t=2015-07-28T20:00:00.000-2015-07-28T20:20:00.000||The complete eight o’clock news program without the weather as a VOD manifest.|
The above scenario is ideal if you have for example a 24 hour rolling DVR window for Live.
If you would like to run a catch-up service with a larger window, say 7-10 days, using Unified Capture would be a much better fit. Using the same time notation and feature set, the live streams can be archived to disk as they become available. Please read more about it here: Capturing LIVE.
Restart and Catch-up TV is supported for HLS and MPEG-DASH (isoff-live profile) playout.
A specific use case of the second scenario in above section is ‘Blanking’ where the origin makes streams unavailable for a specific time to all or only specific users, for instance becasue streaming rights do not include certain content or because user A has a premium subscription and user B has not.
For example, a service provider acquires the right to stream certain TV-channels, and gets the rights for sports as well - but sports are only available for a premium subscription.
Say the game starts at 20:30, then when Pippin joins to view at 19:50 he is handed a manifest which is only valid until 20:30. Simon on the other hand has the premium option and gets the full stream.
In the case of Pippin the CMS has to tag begin and end time in the future onto his manifest request.
So Pippin’s player will request something like this:
Whereas Simon’s player will request the plain URL: