Conditional Playback

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Conditional Playback

SMIL features the expr tag for defining conditions during which a media item is played. This is can be applied to 

  • Limiting the "validity period" within which a media file is licensed to play
  • Defining items that only play on certain days of the week
  • Allowing micro adjustment to playlists based on player ID/meta-data
  • The general format to specifying a conditional play is by adding the expr tag to a media item, such as
<seq repeatCount="indefinite">
   <seq>
      <video src="everyday.mp4" />
      <video src="mondays.mp4" expr="1=weekday()" />
   </seq>
</seq>

Only when the expression provided evaluates to true is the associated media item played.

In the sample code, item "everyday.mp4" is played every day the player is on, while item "mondays.mp4" is only played on Mondays.

Supported Functions

The content of the expr tag is an HTML-encoded XPath expression. Following player-specific run-time conditional functions:

 
Function name Description Example (Shown with HTML-encoding)
smil-playerId() Returns playerId defined in Timing config as playerId in lower case. expr="compare(smil-playerId(),'f1835d9f-be8f-4054-9e6c-123456789012')"
smil-playerName() Returns player name defined in Timing config as playerName. expr="compare(smil-playerName(),'Entrance')"
date() Returns player's local date-time in ISO8601 format. expr="compare(date(),'2021-01-01T00:00:00')<0"
gmdate() Returns player's UTC date-time in ISO8601 format (ending in UTC indicator "Z"). expr="compare(gmdate(),'2021-01-01T00:00:00Z')<0"
time() Returns player time in HH:MM:SS, 24 hours format expr="compare(time(),'16:29:15')<0"
weekday() Returns a number from 0 (Sunday) to 6 (Saturday) indicating player's local day-of-week. expr="weekday()=1"
gmweekday() Returns a number from 0 (Sunday) to 6 (Saturday) indicating player's UTC day-of-week. expr="gmweekday()=1"
compare(string comp1, string comp2) Returns -1 if comp1 is "less" than comp2 as a string, 0 if equal, 1 if "greater". expr="compare(date(),'2021-01-01T00:00:00')<0"

If you are working with a legacy implementation of the SMIL, you are probably using adapi- prefix for functions above. You can keep using it, signageOS SMIL Player supports these functions with or without the adapi- prefix.

compare() in detail

compare() compares two inside arguments. The result of the comparison is then evaluated against >= and <.

 

Example compare() output Expression result
compare(5, 10) -1 --
compare(10, 10) 0 --
compare(20, 10) 1 --
compare('2021-01-01T00:00:00', '2021-02-28T00:00:00') > 0 -1 false
compare('2021-01-01T00:00:00', '2021-01-01T00:00:00') >= 0 0 true
compare('2021-12-31T00:00:00', '2021-01-01T00:00:00') > 0 1 true

Usage

Single condition

Play from Wednesday to Saturday

The weekday()>=3 says to be true and activate the <par> playlist every time the day of the week is >= Wednesday.

This playlists will then be active every Wednesday, Thursday, Friday, Saturday.

<par expr="weekday()>=3">
    <!-- indefinite loop of media files in the selected order -->
    <seq repeatCount="indefinite">
        <video src="https://static.signageos.io/assets/video-test-1_e07fc21a7a72e3d33478243bd75d7743.mp4" region="top-left" soundLevel="0%"></video>
        <img dur="3" src="https://signageos-demo.s3.eu-central-1.amazonaws.com/smil/samples/assets/landscape1.jpg" region="top-left" fit="fill"></img>
    </seq>
</par>

Play from 25th of January 2021

The compare(date(),'2021-01-25T00:00:00')>=0 is valid and true every day since 25th of Jan 2021.

  • compare() returns -1 if date() is less than '2021-01-25T00:00:00'
  • compare() returns 0 if date() is equal to '2021-01-25T00:00:00'
  • compare() returns 1 if date() is higher than '2021-01-25T00:00:00'

The <par> playlist will be active from 25th of Jan onwards.

<par expr="compare(date(),'2021-01-25T00:00:00')>=0">
    <!-- indefinite loop of media files in the selected order -->
    <seq repeatCount="indefinite">
        <video src="https://static.signageos.io/assets/video-test-1_e07fc21a7a72e3d33478243bd75d7743.mp4" region="top-left" soundLevel="0%"></video>
        <img dur="3" src="https://signageos-demo.s3.eu-central-1.amazonaws.com/smil/samples/assets/landscape1.jpg" region="top-left" fit="fill"></img>
    </seq>
</par>

Play from Sunday to Wednesday between 1st of Jan to 1st of Feb

You can mix and match wallclock begin and end attributes and expressions to get the desired behavior

<par begin="wallclock(R/2021-01-01T00:00:00/P1D)" end="wallclock(R/2021-02-01T23:59:59/P1D)" expr="weekday()<=3">
    <!-- indefinite loop of media files in the selected order -->
    <seq repeatCount="indefinite">
        <video src="https://static.signageos.io/assets/video-test-1_e07fc21a7a72e3d33478243bd75d7743.mp4" region="top-left" soundLevel="0%"></video>
        <img dur="3" src="https://signageos-demo.s3.eu-central-1.amazonaws.com/smil/samples/assets/landscape1.jpg" region="top-left" fit="fill"></img>
    </seq>
</par>
 

More About Wallclock

Robust time mechanism handling dates, times, recurring events and more.

Multiple compound conditions

For a more complex use cases you can combine multiple conditions with logical AND, and OR.

Simple combinations

Simple combinations of conditions are achieved by using AND and OR in between conditions.

Plays on Sunday or Saturday:

weekday()=0 or weekday()=6

Complex combinations

Complex combinations are also using AND and OR, but you can wrap a sequence of conditions in [] and combine multiple conditions in one expression.

Plays from Monday to Friday between 9:00 - 16:00 or Saturday and Sunday between 10:00 and 15:00

// final expression
[weekday()>=1 and weekday()<=5 and compare(time(), '09:00:00')>0 and compare(time(), '16:00:00')<0] or [[weekday()=0 or weekday()=6] and compare(time(), '10:00:00')>0 and compare(time(), '15:00:00')<0]

// human readable
[
    weekday()>=1 
    and 
    weekday()<=5 
    and 
    compare(time(), '09:00:00')>0 
    and 
    compare(time(), '16:00:00')<0
] 
or 
[
    [
        weekday()=0 or weekday()=6
    ] 
    and 
    compare(time(), '10:00:00')>0 
    and 
    compare(time(), '15:00:00')<0
]

More Examples

Play on Sunday or Saturday

The following expression will activate playlist on Saturday and Sunday:
weekday()=0 or weekday()=6

<par expr="weekday()=0 or weekday()=6">
    <!-- indefinite loop of media files in the selected order -->
    <seq repeatCount="indefinite">
        <video src="https://static.signageos.io/assets/video-test-1_e07fc21a7a72e3d33478243bd75d7743.mp4" region="top-left"></video>
        <img dur="3" src="https://signageos-demo.s3.eu-central-1.amazonaws.com/smil/samples/assets/landscape1.jpg" region="top-left"></img>
    </seq>
</par>

Play between 25th of Jan and 29th of Jan (including)

The following expression is comparing date via compare and checking whether the date is greater than 25th of Jan and less than 30th of Jan.
compare(date(), '2021-01-25T00:00:00')>0 and compare(date(), '2021-01-29T23:59:59')<=0

<par expr="compare(date(), '2021-01-25T00:00:00')>0 and compare(date(), '2021-01-29T23:59:59')<=0">
    <!-- indefinite loop of media files in the selected order -->
    <seq repeatCount="indefinite">
        <video src="https://static.signageos.io/assets/video-test-1_e07fc21a7a72e3d33478243bd75d7743.mp4" region="top-left"></video>
        <img dur="3" src="https://signageos-demo.s3.eu-central-1.amazonaws.com/smil/samples/assets/landscape1.jpg" region="top-left"></img>
    </seq>
</par>

Next steps

 

Source: a-smil.org

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