Power Studio

This module lets you control Power Studio from Bitfocus Companion.

Use it to build Stream Deck pages for playout transport, cart players, playlist set-next control, the mix editor and the recorder. The module also reads status from Power Studio, so buttons can change color and show the current artist, title or cart name.

About Power Studio

Power Studio is broadcast radio automation software from HOPLA Productions.

It is designed as a complete radio workflow system: playout, music scheduling, voice tracking, automatic content ingestion, commercial planning, news bulletin building and integration with studio hardware or content providers all live in the Power Studio ecosystem.

This Companion module focuses on the parts that make sense on a button surface during live operation:

• Player transport.
• Cart player control.
• Playlist set-next control.
• Mix editor transport.
• Recorder transport and recording control.
• Visual status feedback on buttons.
• Trigger-friendly variables and feedbacks for Companion automation.

More information about Power Studio is available at power-studio.nl.

Version History

Version 1.0.3

• Re-tagged the release after fixing the package lockfile/tooling setup for Bitfocus build checks.
• Updated project workflows to install dependencies and build packages with Yarn.

Version 1.0.2

• Refresh status immediately after button actions so feedback updates faster without overlapping regular polls.

Version 1.0.1

• Addressed Bitfocus review feedback.
• Switched the module to Yarn lockfile/package-manager metadata.
• Removed the local Companion tools patch script.
• Improved polling so status refreshes no longer overlap.
• Raised the poll interval defaults to reduce load while keeping button state responsive.
• Added stricter validation and variable support for the set-next-item action.

Version 1.0.0

• First release.

Setup

Add a Power Studio connection in Companion and enter the address of the Power Studio REST API.

• In Power Studio, configure and enable the REST API Plugin.
• Use the Power Studio host name or IP address.
• Set the API port to the same port number configured in the Power Studio REST API Plugin.
• The default REST API Plugin port is 9876, and the Companion module uses 9876 as its default port too.
• Leave the path prefix empty unless the API is published behind a reverse proxy.
• Recommended: leave Authenticate request using Basic Auth. disabled in the Power Studio REST API Plugin.
• Recommended: leave the module Username and Password fields empty.
• When Basic Auth is disabled, the REST API uses the credentials of the user currently logged into Power Studio. If no user is logged into Power Studio, authorization fails with HTTP 401.
• When Basic Auth is enabled, enter the module username and password. The module can then authenticate even when no user is logged into Power Studio, but Playout, Carts, Mix Editor, Recorder and Playlist Window control cannot be operated until a user is logged into Power Studio.
• Keep the default poll interval of 500 ms unless you need faster or slower button updates. The minimum is 100 ms.
• Use the three title display options when long titles make buttons hard to read. They control cart rack presets, player transport presets and playlist window presets separately.

Power Studio version 1.24.1 or newer is required. If an older version is detected, the connection status shows Power Studio version 1.24.1 or newer is required.

When the connection is not OK, preset buttons turn dark gray. This includes missing configuration, a bad connection, authentication problems and unsupported Power Studio versions. Companion's own connection indicator shows authentication failures with a yellow/orange warning triangle and missing connections with a red warning triangle. While the module is disabled or restarting, presets use dark gray as their base color until feedbacks are active again.

When the connection is OK, start by dragging presets to buttons. Presets created with this module version include text feedback, so the title display options can be changed later and the placed buttons will update. The text feedback uses the current Companion connection label for variables, such as $(Power_Studio:cart_a_slot_1_title). Buttons created with an older module version may need to be dragged from the preset list once more.

Recommended Pages

A practical first layout is:

• One player transport page with Play, Cue or stop and PFL for Player A through Player D.
• One cart page with rack slots 1 through 7 for Cart A and Cart B.
• One mix editor page with play, stop, record, save, undo and mix navigation.
• One recorder page with play, stop, record and recorder profile navigation.
• One playlist page with 16 set-next buttons and previous/next/reset window buttons.
• One small diagnostics area showing connection status and the latest command error.

Numbering

Power Studio names the players and carts with letters. The module shows those same names in presets, actions, feedbacks and variables.

Item	Numbering
Playout players	Player A, Player B, Player C and Player D
Cart players	Cart A and Cart B
Cart rack slots	1 through 7
Playlist window items	1 through 16

Presets

Presets are the easiest way to build reliable buttons. They already include actions, text variables and feedback colors. All presets also include connection feedback, so they turn dark gray when Companion is not connected cleanly to Power Studio.

Preset Overview

Section	Presets
Playout players	Player A Play, Player A Cue or stop, Player A PFL toggle, repeated through Player D.
Playout control	Refresh playout, Load next playlist, Automation mode, Live Assist mode, Training Mode.
Carts	Trigger Cart A slot 1 through Trigger Cart A slot 7, Stop Cart A, repeated for Cart B.
Mix Editor	Mix play, Mix stop, Mix record, Mix save, Mix undo, Previous mix, Next mix, Previous profile, Next profile, Select profile.
Recorder	Recorder play, Recorder stop, Recorder toggle recording, Recorder start recording, Recorder stop recording, Recorder previous profile, Recorder next profile, Recorder select profile.
Playlist Window	Set next playlist window item 1 through Set next playlist window item 16, Previous playlist window, Next playlist window, Reset playlist window.

Player Transport

Each of the four players has:

Preset	Function
PLAY A	Sends Play to Player A.
CUE A	Sends Cue when Player A is stopped or idle. Sends Stop when Player A is playing.
PFL A	Sends PflToggle to Player A.

By default these presets show live artist and title below the button label. You can hide those title lines with the player transport title display option, leaving compact labels such as PLAY A, CUE A and PFL A.

Player colors:

Button	Color	Meaning
PLAY	Dark gray	Player is empty
PLAY	Dark gray	Power Studio is in Automation mode and this player is not playing; player transport is unavailable
PLAY	Blue	Player has an item loaded
PLAY	Yellow	Player is next
PLAY	Green	Player is playing, also when Power Studio is in Automation mode
CUE	Dark gray	Player is empty or already cued
CUE	Dark gray	Power Studio is in Automation mode; player transport is unavailable
CUE	Orange	Player is stopped but not cued; pressing cues the player
CUE	Red	Player is playing; pressing stops the player
PFL	Dark gray	PFL is inactive
PFL	Dark gray	Power Studio is in Automation mode; player transport is unavailable
PFL	Yellow	PFL is active

When Power Studio is in Automation mode, non-playing player transport buttons become dark gray because they cannot be operated. A playing player still shows green on the Play preset, so you can see which player is currently on air. When the connection is not OK, dark gray wins over all player colors.

Playout Control

Preset	Function
REFRESH PLAYOUT	Refreshes the Power Studio playlist.
NEXT PLAYLIST	Loads the next playlist.
AUTO	Switches to Automation mode.
LIVE ASSIST	Switches to Live Assist mode.
TRAINING MODE	Switches to Training Mode.

Playout control colors:

Button	Color	Meaning
REFRESH PLAYOUT	Blue	Connection is OK and the command is available
NEXT PLAYLIST	Blue	Connection is OK and the command is available
AUTO	Blue	Connection is OK and Automation mode is not active
AUTO	Yellow	Automation mode is active
LIVE ASSIST	Blue	Connection is OK and Live Assist mode is not active
LIVE ASSIST	Yellow	Live Assist mode is active
TRAINING MODE	Blue	Connection is OK and Training Mode is not active
TRAINING MODE	Yellow	Training Mode is active

When the connection is not OK, dark gray wins over all playout control colors.

Cart Rack

There are two cart players. Each cart player always has seven rack slots.

• Cart A: CART A:1 through CART A:7
• Cart B: CART B:1 through CART B:7

The button name stays tied to the rack position. By default the visible button text also follows the title currently loaded in that rack slot. This means you can keep the same Stream Deck page while Power Studio loads different carts. If long cart titles make the page hard to read, hide cart rack titles in the module configuration; the buttons then keep compact labels such as CART A:1.

Cart colors:

Button	Color	Meaning
CART A:1 through CART B:7	Dark gray	Rack slot is empty or None
CART A:1 through CART B:7	Blue	Rack slot is loaded
CART A:1 through CART B:7	Yellow	Rack slot is selected
CART A:1 through CART B:7	Green	Rack slot is playing
CART A STOP / CART B STOP	Dark gray	Cart player is not playing
CART A STOP / CART B STOP	Red	Cart player is playing

When the connection is not OK, dark gray wins over all cart status colors.

Mix Editor

Preset	Function
MIX PLAY	Play in the mix editor.
MIX STOP	Stop mix editor playback or recording.
MIX REC	Start recording in the mix editor.
MIX SAVE	Save the current mix.
MIX UNDO	Undo the last mix editor change.
PREV MIX	Move to the previous mix.
NEXT MIX	Move to the next mix.
PREV PROFILE	Move to the previous profile.
NEXT PROFILE	Move to the next profile.
SELECT PROFILE	Select a profile.

Mix editor colors:

Button	Color	Meaning
MIX PLAY	Dark gray	Play is unavailable
MIX PLAY	Blue	Play is available
MIX PLAY	Green	Mix editor is playing
MIX STOP	Dark gray	Stop is unavailable
MIX STOP	Red	Stop is available, playing, or recording
MIX REC	Dark gray	Record is unavailable
MIX REC	Blue	Record is available
MIX REC	Red	Mix editor is recording
MIX SAVE	Dark gray	Save is unavailable
MIX SAVE	Blue	Save is available
MIX UNDO	Dark gray	Undo is unavailable
MIX UNDO	Blue	Undo is available
PREV MIX	Dark gray	Previous mix is unavailable
PREV MIX	Blue	Previous mix is available
NEXT MIX	Dark gray	Next mix is unavailable
NEXT MIX	Blue	Next mix is available
PREV PROFILE / NEXT PROFILE / SELECT PROFILE	Blue	Connection is OK and the command is shown as available

Profile navigation buttons turn blue when connected because the current Power Studio API does not report separate availability states for profile navigation.

When the connection is not OK, dark gray wins over the mix editor colors.

Recorder

Preset	Function
REC PLAY	Plays the current recorder item.
REC STOP	Stops recorder playback or recording.
REC TOGGLE	Toggles recorder recording.
REC START	Starts recorder recording.
STOP REC	Stops recorder recording.
PREV PROFILE	Moves to the previous recorder processing profile.
NEXT PROFILE	Moves to the next recorder processing profile.
SELECT PROFILE	Selects the currently previewed recorder processing profile.

Recorder colors:

Button	Color	Meaning
REC PLAY	Dark gray	Play is unavailable
REC PLAY	Blue	Play is available
REC PLAY	Green	Recorder is playing
REC STOP	Dark gray	Stop is unavailable
REC STOP	Red	Stop is available, playing, or recording
REC TOGGLE	Dark gray	Recording cannot be started
REC TOGGLE	Blue	Recording can be started
REC TOGGLE	Red	Recorder is recording
REC START	Dark gray	Recording cannot be started
REC START	Blue	Recording can be started
REC START	Red	Recorder is already recording
STOP REC	Dark gray	Recorder is not recording
STOP REC	Red	Recorder is recording
PREV PROFILE / NEXT PROFILE / SELECT PROFILE	Dark gray	Processing profile changes are unavailable
PREV PROFILE / NEXT PROFILE / SELECT PROFILE	Blue	Processing profile changes are available

When the connection is not OK, dark gray wins over the recorder colors.

Playlist Window

The playlist window gives you 16 visible set-next buttons.

Preset	Function
NEXT 1 through NEXT 16	Sets the visible playlist item as next.
PREV WINDOW	Moves the visible window 16 items back.
NEXT WINDOW	Moves the visible window 16 items forward.
RESET WINDOW	Jumps back to the first playlist item.

By default playlist buttons show artist and title below NEXT 1 through NEXT 16. You can hide those title lines with the playlist window title display option. The color indicates the content type or active state.

Button	Color	Meaning
NEXT 1 through NEXT 16	Dark gray	Empty or default
NEXT 1 through NEXT 16	Blue	Track
NEXT 1 through NEXT 16	Purple	Jingle
NEXT 1 through NEXT 16	Cyan	Promo
NEXT 1 through NEXT 16	Orange	Spot
NEXT 1 through NEXT 16	Magenta	VoiceTrack
NEXT 1 through NEXT 16	Slate gray	Misc
NEXT 1 through NEXT 16	Yellow	Next item
NEXT 1 through NEXT 16	Green	Currently playing
PREV WINDOW / NEXT WINDOW / RESET WINDOW	Blue	Connection is OK and the command is available

When the connection is not OK, dark gray wins over the playlist item colors.

Actions

Actions are available when you want to build your own buttons instead of starting from presets.

Action	Options	What it does
Refresh cached status	None	Polls Power Studio immediately and updates button feedbacks and variables.
Playout: send player command	Player A to Player D; command	Sends a transport or PFL command to a playout player. Cue uses the same smart cue-or-stop behavior as the Cue preset.
Playout: cue or stop player	Player A to Player D	Sends Stop when the player is playing, otherwise sends Cue.
Playout: set mode	Mode	Changes Power Studio playout mode.
Playout: load next playlist	None	Loads the next playlist.
Playout: refresh playlist	None	Refreshes the current Power Studio playout playlist.
Playout: set next item	Program line id	Sets a playlist line as next by its global line id.
Playlist: set next visible item	Item 1 to 16	Sets the visible playlist window item as next.
Playlist: previous window	None	Moves the visible playlist window 16 items back.
Playlist: next window	None	Moves the visible playlist window 16 items forward.
Playlist: reset window	None	Resets the visible playlist window to the first item.
Playlist: set window offset	Offset 0 to 999	Jumps the visible playlist window to a zero-based playlist offset.
Carts: trigger rack slot	Cart A or Cart B; rack slot 1 to 7	Triggers a cart rack slot.
Carts: stop cart player	Cart A or Cart B	Stops the selected cart player.
Mix editor: command	Command	Sends a mix editor command.
Recorder: command	Command	Sends a recorder command.

Player commands:

• Play
• Stop
• Cue
• StopAndCue
• PflOn
• PflOff
• PflToggle

Playout modes:

• Automation
• LiveAssist
• TrainingMode

Mix editor commands:

• play
• stop
• record
• save
• undo
• previousmix
• nextmix
• previousprofile
• nextprofile
• selectprofile

Recorder commands:

• play
• stop
• record
• record_start
• record_stop
• previous_profile
• next_profile
• select_profile

Feedbacks

Feedbacks let buttons change style based on the latest status read from Power Studio.

Feedback	Options	True when
Power Studio connection is OK	None	Companion's connection status for this module is OK.
Power Studio connection is not OK	None	Companion's connection status for this module is anything other than OK. Presets use this to turn buttons dark gray during bad or missing connections.
Any player is playing	None	One or more playout players are playing.
Any cart is playing	None	One or more cart players are playing.
Playout mode is active	Mode	Power Studio is in the selected playout mode.
On-air state is active	OffAir or OnAir	Power Studio reports the selected on-air state.
Player state is active	Player A to Player D; state	The selected player has the selected state active.
Player has item loaded	Player A to Player D	The selected player has a title, artist, duration or track id.
Player is empty	Player A to Player D	The selected player is known and has no title, artist, duration or track id.
Player transport preset text follows title setting	Player A to Player D; transport	Updates preset text when the player transport title display option changes. Automatically included in player transport presets.
Cart is playing	Cart A or Cart B	The selected cart player is playing.
Cart rack slot has status	Cart A or Cart B; rack slot 1 to 7; status	The selected rack slot has the selected status. Empty slots count as None.
Cart rack preset text follows title setting	Cart A or Cart B; rack slot 1 to 7	Updates preset text when the cart rack title display option changes. Automatically included in cart rack presets.
Playlist window item state is active	Item 1 to 16; state	The visible playlist item exists, is playing or is next.
Playlist window item has content type	Item 1 to 16; content type	The visible playlist item has the selected content type.
Playlist window preset text follows title setting	Item 1 to 16	Updates preset text when the playlist window title display option changes. Automatically included in playlist window item presets.
Mix editor state is active	State	The mix editor reports the selected state as active.
Recorder state is active	State	The recorder reports the selected state as active.

Player states:

• playing
• cued
• pfl
• isNextItem

Cart rack statuses:

• None
• Loaded
• Selected
• Playing

Playlist item states:

• hasItem
• isPlaying
• isNextItem

Playlist content types:

• Track
• Jingle
• Promo
• Spot
• VoiceTrack
• Misc

Mix editor states:

• playing
• recording
• canPlay
• canStop
• canSave
• canUndo
• canGoPreviousMix
• canGoNextMix
• canRecordMix
• canPlayNext

Recorder states:

• playing
• recording
• stopped
• canPlay
• canStop
• canStartRecord
• canChangeProcessingProfile

Companion Triggers

Companion triggers live in Companion's Triggers tab. A trigger has:

• An event, often On variable change.
• An optional condition, often one of this module's feedbacks.
• Actions, which can be Power Studio actions or actions from other Companion connections.

This module exposes trigger-friendly variables and feedbacks. Use variables when you want to react to a state change, and feedbacks when you want to filter whether the trigger should run.

Useful variables for triggers:

Variable	Use
connection_ok	Detect connection loss or recovery.
any_player_playing	Detect that playout started or stopped.
any_cart_playing	Detect that any cart started or stopped.
active_player	Name of the first currently playing player.
current_track_id	Track id of the first currently playing player.
current_track_artist	Artist of the first currently playing player.
current_track_title	Title of the first currently playing player.
next_player	Name of the player that is marked as next.
next_track_id	Track id of the next player.
next_track_artist	Artist of the next player.
next_track_title	Title of the next player.
active_cart	Name of the first currently playing cart.
cart_a_playing / cart_b_playing	Detect a specific cart player.
playlist_item_1_is_next_item	Detect when a visible playlist item becomes next. Replace 1 with item 1 through 16.
mix_editor_recording	Detect mix editor recording state.
recorder_recording	Detect recorder recording state.
recorder_playing	Detect recorder playback state.

Useful feedbacks as trigger conditions:

Feedback	Use
Power Studio connection is OK	Run only while the module is connected.
Power Studio connection is not OK	Run only while the module is disconnected or in a bad state.
Any player is playing	Run only while playout is active.
Any cart is playing	Run only while at least one cart is active.
Player has item loaded	Run only when the selected player has content loaded.
Player is empty	Run only when the selected player is empty.
Playout mode is active	Run only in Automation, Live Assist or Training Mode.
Recorder state is active	Run only when the selected recorder state is active.

Example trigger recipes:

Goal	Event	Condition	Action idea
Show a warning when Power Studio disconnects	connection_ok changes	Power Studio connection is not OK	Press an internal warning button or trigger a light.
Turn on an on-air tally when playout starts	any_player_playing changes	Any player is playing	Control a GPIO, HTTP device or lighting system.
Show that a cart is active	any_cart_playing changes	Any cart is playing	Trigger a cart-active tally or page change.
React when a playlist item becomes next	playlist_item_1_is_next_item changes	Value is true, or use playlist item feedback	Run an external command or update another Companion page.
Show mix recording state	mix_editor_recording changes	Value is true	Trigger a recording lamp or notification.
Show recorder recording state	recorder_recording changes	Value is true	Trigger a recorder lamp or notification.

Variables

You can place variables in button text. Use this Companion syntax:

$(hopla-powerstudio:variable_name)

If you rename the Companion connection, use that connection label instead of hopla-powerstudio.

Connection And API Variables

Variable	Meaning
connection_status	Current Companion connection status text.
connection_ok	Whether the Companion connection status for this module is OK.
last_status_error	Latest error while polling Power Studio status.
last_command_error	Latest error while running a button command.
version	Current Power Studio version while the module connection is OK. Empty when the connection is not OK.
build	Current Power Studio build while the module connection is OK. Empty when the connection is not OK.
last_detected_power_studio_version	Last Power Studio version successfully read from the REST API.
last_detected_power_studio_build	Last Power Studio build successfully read from the REST API.
parsed_power_studio_version	Version parser output used by the module for compatibility checks.
power_studio_minimum_supported_version	Minimum Power Studio version supported by this module.
power_studio_version_supported	Whether the detected Power Studio version is supported.
enabled_capabilities	Capabilities currently enabled by version detection.
uptime	Power Studio application uptime.
last_updated	Last successful status update timestamp.

Playout Variables

Variable	Meaning
playout_mode	Current playout mode.
on_air_state	Current on-air state.
any_player_playing	Whether one or more playout players are playing.
active_player	Name of the first currently playing player.
current_track_id	Track id of the first currently playing player.
current_track_artist	Artist of the first currently playing player.
current_track_title	Title of the first currently playing player.
next_player	Name of the player that is marked as next.
next_track_id	Track id of the next player.
next_track_artist	Artist of the next player.
next_track_title	Title of the next player.
next_playlist_time_mode	Current next playlist time mode.
next_start_time	Next start time reported by Power Studio.

Player variables use the player letter. Replace a with a, b, c or d:

Variable pattern	Meaning
player_a_artist	Artist loaded on Player A.
player_a_title	Title loaded on Player A.
player_a_playing	Whether Player A is playing.
player_a_cued	Whether Player A is cued.
player_a_pfl	Whether Player A has PFL active.
player_a_position	Current playback position for Player A, in seconds.
player_a_duration	Current item duration for Player A, in seconds.

Cart Variables

Cart-related variables include aggregate trigger helpers and per-cart variables. For per-cart variables, replace a with a or b:

Variable pattern	Meaning
any_cart_playing	Whether one or more cart players are playing.
active_cart	Name of the first currently playing cart.
cart_a_playing	Whether Cart A is playing.
cart_a_position	Current playback position for Cart A, in seconds.
cart_a_duration	Current item duration for Cart A, in seconds.
cart_a_play_mode	Current play mode for Cart A.

Cart rack variables exist for rack slots 1 through 7. Replace a and 1 with the cart letter and rack slot:

Variable pattern	Meaning
cart_a_slot_1_title	Title loaded in Cart A, rack slot 1.
cart_a_slot_1_status	Status of Cart A, rack slot 1.

Playlist Window Variables

Variable	Meaning
playlist_window_offset	Zero-based offset of the current playlist window.
playlist_window_first_item	Human-friendly number of the first visible playlist item.

Playlist item variables exist for visible items 1 through 16. Replace 1 with the visible item number:

Variable pattern	Meaning
playlist_item_1_has_item	Whether visible item 1 exists.
playlist_item_1_line_id	Global line id of visible item 1.
playlist_item_1_artist	Artist of visible item 1.
playlist_item_1_title	Title of visible item 1.
playlist_item_1_content_type	Content type of visible item 1.
playlist_item_1_duration	Duration of visible item 1.
playlist_item_1_start_time	Start time of visible item 1.
playlist_item_1_is_playing	Whether visible item 1 is currently playing.
playlist_item_1_is_next_item	Whether visible item 1 is the next item.

Mix Editor Variables

Variable	Meaning
mix_editor_playing	Whether the mix editor is playing.
mix_editor_recording	Whether the mix editor is recording.
mix_editor_can_play	Whether play is currently available.
mix_editor_can_stop	Whether stop is currently available.
mix_editor_can_save	Whether save is currently available.
mix_editor_can_undo	Whether undo is currently available.
mix_editor_can_go_previous_mix	Whether previous mix is currently available.
mix_editor_can_go_next_mix	Whether next mix is currently available.
mix_editor_can_record_mix	Whether record is currently available.
mix_editor_can_play_next	Whether play next is currently available.

Recorder Variables

Variable	Meaning
recorder_file_name	File name of the current recorder item, when available.
recorder_playing	Whether the recorder is playing.
recorder_recording	Whether the recorder is recording.
recorder_stopped	Whether the recorder is stopped.
recorder_position	Current recorder position, in seconds.
recorder_duration	Current recorder duration, in seconds.
recorder_can_play	Whether recorder play is currently available.
recorder_can_stop	Whether recorder stop is currently available.
recorder_can_start_record	Whether recorder recording can be started.
recorder_can_change_processing_profile	Whether recorder processing-profile changes are currently available.

Troubleshooting

If buttons stay dark gray, the module connection is not OK. Check the connection settings and put connection_status or last_status_error on a temporary button. A yellow/orange warning triangle usually points to authentication failure; a red warning triangle usually points to no connection.

If last_status_error says values could not be retrieved from the Power Studio REST API, check the host, port, path prefix, Basic Auth setting, credentials and whether the REST API Plugin is enabled in Power Studio.

If authorization fails with Basic Auth disabled, check whether a user is currently logged into Power Studio. If authorization fails with Basic Auth enabled, check the module username and password.

If the module is connected but commands cannot be operated, check whether a user is currently logged into Power Studio.

If the connection status says Power Studio version 1.24.1 or newer is required, the REST API is reachable but the Power Studio version is too old for this module.

If a command does not work, put last_command_error on a temporary button. This usually tells you whether Power Studio rejected the command, the item no longer exists, the API cannot be reached, or the current Power Studio state does not allow the command.

If a playlist button sets the wrong item as next, check the current playlist window. Use PREV WINDOW, NEXT WINDOW and RESET WINDOW, and show playlist_window_first_item on the page.

If a cart button has no title, the rack slot is probably empty. Empty rack slots intentionally show as None.