Synchronized playback across players (PiSignage 5.6.0)

Overview

Synchronized playback makes every player in a group show the same playlist item at the same moment. Turn on one group setting, Sync playback, and players running PiSignage 5.6.0 switch assets together within about one second, with no cabling, no master player and no extra server traffic.

It is built for rows of screens that should read as one: a bank of displays in a lobby, menu boards side by side, a corridor of portrait screens, or retail shelves that advertise the same product at once. Each player follows its own clock, so the players do not need to talk to each other and a player that reboots simply rejoins the others where they are.

What to expect:

• Players change to the next image or video within about 0.3 to 1 second of each other.
• A player that boots, changes playlist or comes back from an advert joins mid-item and seeks into the running video.
• Shuffle still works: all players use the same shuffled order, and the order changes every cycle.
• This is not a frame-accurate video wall. One video spread across several screens needs dedicated video-wall hardware.

Sync also works across groups. Two groups stay in step as long as their playlists have the same duration in every row, in the same order; the assets themselves can differ. A lobby group and a corridor group can show different content and still switch at the same moment. Keep Shuffle content off for this, because the shuffled order is derived from the file names and would differ between the two playlists.

Requirements

Synchronized playback needs players on 5.6.0, a server that knows the setting, internet time on every player, and a regular playlist of fixed-length items.

Notes on the clock: Raspberry Pi boards have no battery-backed clock, so they rely on NTP after every boot. On a network that blocks outbound NTP, point the players at a local NTP server. The player checks timedatectl every minute and logs when the clock moves in or out of sync.

Every player works out the timeline on its own, so there is no limit on the number of players in a group and no extra load on the server.

Which content types take part

Any row with a fixed duration takes a time slot, so players switch to it and away from it together. What differs is whether a player joining mid-slot can catch up inside the item.

Step-by-step: setting up synchronized playback

The whole setup is one switch on the group's Playback tab, followed by a deploy. The steps below assume the players are already registered on pisignage.com and placed in a group.

Step 1. Update the players to 5.6.0

1. Open Players in the PiSignage web interface.
2. Check the version chip under each player's name, next to its ID and IP address. Every player that will take part must show 5.6.0 or later.
3. For an older player, select it and use Update player to 5.6.0. Wait until the player reports back online with the new version.

Step 2. Put the players in one group

1. Open Groups and open the group that will hold the synchronized screens, or create a new one.
2. On the Screens tab, confirm that every player that should stay in step is listed. Players in other groups are not affected.

Step 3. Build a playlist with fixed durations

1. Open Playlists and create or edit the playlist for the group.
2. Give every image, web page and widget a duration. Videos use their own length.
3. Do not add .mrss feed rows or .local folder rows to this playlist. They have no fixed length, and the player turns sync off for the whole playlist while one is present.
4. Save the playlist.

Step 4. Turn on Sync playback across players

1. Open the group and select the Playback tab.
2. In the Playback Options card, find Sync playback across players. It sits just below Shuffle content and reads "Screens in groups with Sync enabled play the same content at the same time, for all playlists except those with RSS feeds or cloud folders".
3. Turn the switch on.
4. Leave Time to stop video at 0 on the group's Settings tab. Shuffle may stay on; all players will use the same shuffled order.
5. Click Save Changes.

Step 5. Assign the playlist and deploy

1. On the Playlists tab, set the playlist as the group's default playlist, or add it to the schedule.
2. Click Deploy. A toast at the bottom right confirms "Deploy done successfully" once the players have been sent the new settings and content.

Step 6. Check the screens

1. Stand where two or more of the screens are visible. Within a minute they should be showing the same item and switch to the next one together.
2. A player that was downloading content joins once its files are complete. A player that reboots joins mid-item, seeking into a video that is already running on the others.

You can also check from the server without being on site. On the Screens page, open Screen Details for two players in the group and keep the Feed tabs open side by side. Both feeds show the same item and advance together.

Optional: confirm from the player log

On a player, the log file /home/pi/forever_out.log records when sync starts and the timeline it follows. Search it with:

grep -ia "Sync playback" /home/pi/forever_out.log

A healthy player prints the timeline it is following, for example:

Sync playback: 6 slots, cycle 95s, timeline id 3a9f1c2e

If the setting is on but cannot be applied, one warning line names the reason:

Sync playback is enabled but not applied: system clock is not NTP synchronized

How it works

Each player turns the playlist into a fixed timeline and asks its clock which slot is current. There is no master player, no server tick and no player-to-player messaging.

A player that is already playing the current slot carries on. A player that arrives mid-slot, after a boot, a playlist change or an advert, starts the same item and seeks the video to the same offset.

• Fixed slots. Every playlist row gets a slot equal to its duration. The slots repeat back to back from a fixed point in time, so a player's boot time or deploy time does not matter.
• Same answer on every player. The current slot is a pure function of the clock and the playlist rows. Players with the same rows and NTP-synced clocks reach the same answer.
• Slots end on time. An item ends at its slot's absolute end, so a slow start shortens one item rather than pushing every later item back.
• Shared shuffle. With Shuffle content on, the order is drawn from a seed built from the playlist and the cycle number. All players draw the same order, and it changes each cycle.
• Other playlists step aside. Event, play-once and keypress playlists and adverts play as usual. The regular playlist rejoins the timeline afterwards.
• Clock watch. The player checks NTP status at start and every minute. Without a synced clock it plays unsynchronized and rejoins once the clock is good.

Limitations and troubleshooting

Sync keeps screens within about a second of each other and applies only to the main zone of a regular playlist. Side, bottom and other zones, tickers and widgets run as before.

What sync is not:

• Not a video wall. One video cannot be split across several screens, and frame-level alignment is not attempted.
• Not a replacement for identical hardware. Mixed models stay in step, but the slower one starts each item a little later.
• Not applied to the side zones of a multi-zone layout.