diff --git a/admin/event-edit.php b/admin/event-edit.php
index cbd9393..19e36b7 100644
--- a/admin/event-edit.php
+++ b/admin/event-edit.php
@@ -1,715 +1,736 @@
 <?php
 # Linux Day Torino website
 # Copyright (C) 2016, 2017, 2018, 2019, 2020 Valerio Bozzolan, Linux Day Torino
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
 # the Free Software Foundation, either version 3 of the License, or
 # (at your option) any later version.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 # GNU Affero General Public License for more details.
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 /*
  * Event edit
  *
  * From this page you can create/edit an User and assign some skills/interests etc.
  */
 
 // load configurations and framework
 require 'load.php';
 
 // inherit the Conference or specify one
 $conference_uid = $_GET['conference_uid'] ?? $_POST['conference_uid'] ?? CURRENT_CONFERENCE_UID;
 
 // check if the Conference exists
 $conference = ( new QueryConference() )
 	->whereConferenceUID( $conference_uid )
 	->queryRow();
 
 // no Conference no party
 if( !$conference ) {
 	error( "missing conference with UID $conferene_uid" );
 	die_with_404();
 }
 
 // retrieve the Event (if existing)
 $event = null;
 if( isset( $_GET['id'] ) ) {
 
 	// no Event no party
 	$event = ( new QueryEvent() )
 		->whereConference( $conference )
 		->joinConference()
 		->joinChapter( 'LEFT' )
 		->whereEventID( $_GET['id'] )
 		->queryRow();
 
 	// no Event no party
 	if( !$event ) {
 		die_with_404();
 	}
 
 	// no editable no party
 	if( !$event->isEventEditable() ) {
 		missing_privileges();
 	}
 } else {
 	// check if there are permissions to add event
 	if( !has_permission( 'add-event' ) ) {
 		missing_privileges();
 	}
 }
 
 $warning = null;
 
 // check if the user submitted a form
 // check which one
 if( $_POST ) {
 
 	// the user is submitting the save form
 	if( is_action( 'save-event' ) ) {
 
 		$conference_ID = $conference->getConferenceID();
 
 		$data = [];
 		$data[] = new DBCol( Event::TITLE,       $_POST['title'],       's' );
 		$data[] = new DBCol( Event::UID,         $_POST['uid'],         's' );
 		$data[] = new DBCol( Event::LANGUAGE,    $_POST['language'],    's' );
 		$data[] = new DBCol( Event::SUBTITLE,    $_POST['subtitle'],    's' );
 		$data[] = new DBCol( Event::START,       $_POST['start'],       's' );
 		$data[] = new DBCol( Event::END,         $_POST['end'],         's' );
 		$data[] = new DBCol( Event::EXTERNAL_URL,$_POST['url'],         's' );
 		$data[] = new DBCol( Event::ABORTED,     $_POST['aborted'],     'd' );
 		$data[] = new DBCol( Event::IMAGE,       $_POST['image'],       'snull' );
 		$data[] = new DBCol( Chapter::ID,        $_POST['chapter'],     'd' );
 		$data[] = new DBCol( Room::ID,           $_POST['room'],        'd' );
 		$data[] = new DBCol( Track::ID,          $_POST['track'],       'd' );
 		$data[] = new DBCol( Conference::ID,     $conference_ID,        'd' );
 
 		// for each language save the fields
 		foreach( all_languages() as $lang ) {
 			foreach( Event::fields_i18n() as $i18n_column => $label ) {
 				// generic column name in this language
 				$field = $i18n_column . '_' . $lang->getISO();
 
 				// sent column value
 				$value = $_POST[ $field ] ?? null;
 
 				// prepare to be saved
 				$data[] = new DBCol( $field, $value, 'snull' );
 			}
 		}
 
 		// convert empty strings to NULL, if possible
 		foreach( $data as $row ) {
 			$row->promoteNULL();
 		}
 
 		if( $event ) {
 			// update the existing Event
 			( new QueryEvent() )
 				->whereEvent( $event )
 				->update( $data );
 		} else {
 			// insert a new Event
 			Event::factory()
 				->insertRow( $data );
 		}
 
 		$id = $event ? $event->getEventID() : last_inserted_ID();
 
 		// get the updated Event
 		$event = FullEvent::factory()
 			->whereInt( Event::ID, $id )
 			->queryRow();
 
 		// POST-redirect-GET
 		http_redirect( $event->getEventEditURL(), 303 );
 	}
 
 	/**
 	 * Change the Image
 	 */
 	if( $event && is_action( 'change-image' ) ) {
 
 		// prepare the image uploader
 		$image = new FileUploader( 'image', [
 			'category'          => 'image',
 			'override-filename' => "event-" . $event->getEventUID(),
 		] );
 
 		// prepare the image pathnames
 		$img_url  =                $event->getConferenceUID() . _ .  'images';
 		$img_path = ABSPATH . __ . $event->getConferenceUID() . __ . 'images';
 
 		// really upload that shitty image somewhere
 		if( $image->fileChoosed() ) {
 			$ok = $image->uploadTo( $img_path, $status, $filename, $ext );
 			if( $ok ) {
 
 				// now update
 				( new QueryEvent() )
 					->whereEvent( $event )
 					->update( [
 						'event_img' => $img_url . "/$filename.$ext",
 					] );
 
 				// POST-redirect-GET
 				http_redirect( $event->getFullEventEditURL(), 303 );
 
 			} else {
 				$warning = $image->getErrorMessage();
 			}
 		}
 	}
 
 	/*
 	 * Add the user
 	 */
 	if( $event && is_action( 'add-user' ) && isset( $_POST['user'] ) ) {
 		// Add user
 
 		$user = User::factoryFromUID( $_POST['user'] )
 			->select( User::ID )
 			->queryRow();
 
 		if( $user ) {
 			( new QueryEventUser() )
 				->whereEvent( $event )
 				->whereUser(  $user  )
 				->delete();
 
 			( new QueryEventUser() )->insertRow( [
 				new DBCol( Event::ID, $event->getEventID(), 'd' ),
 				new DBCol( User ::ID, $user->getUserID(),   'd' ),
 				new DBCol( EventUser::ORDER, 0,             'd' ),
 			] );
 		}
 	}
 
 	/**
 	 * Update an user order
 	 */
 	if( $event && is_action( 'update-user' ) && isset( $_POST['user'] ) ) {
 
 		$user = User::factoryFromUID( $_POST['user'] )
 			->select( User::ID )
 			->queryRow();
 
 		if( $user ) {
 			if ( !empty( $_POST['delete'] ) ) {
 
 				// delete user
 				( new QueryEventUser() )
 					->whereEvent( $event )
 					->whereUser( $user )
 					->delete();
 
 			} elseif( isset( $_POST['order'], $_POST['role'] ) ) {
 
 				// change order
 				( new QueryEventUser() )
 					->whereEvent( $event )
 					->whereUser( $user )
 					->update( [
 						new DBCol( EventUser::ORDER, $_POST['order'], 'd' ),
 						new DBCol( EventUser::ROLE,  $_POST['role'],  's' ),
 					] );
 			}
 		}
 	}
 
 	// post -> redirect -> get (no: it hide errors)
 	// http_redirect( $_SERVER[ 'REQUEST_URI' ], 303 );
 }
 
 // Event's Sharable(s)
 $sharables = [];
+$users     = [];
 
 if( $event ) {
 
 	// query all the Sharable(s) related to this Event
 	$sharables =
 		( new QuerySharable() )
 			->whereEvent( $event )
 			->queryGenerator();
 
+	// users
+	$users = $event->factoryUserByEvent()
+		->select( [
+			User::UID,
+			User::NAME,
+			User::SURNAME,
+			EventUser::ORDER,
+			EventUser::ROLE,
+		] )
+		->defaultClass( EventUser::class )
+		->orderBy( EventUser::ORDER )
+		->queryResults();
+
 	Header::spawn( null, [
 		'title' => sprintf(
 			__("Modifica %s: %s"),
 			$event->getChapterName(),
 			$event->getEventTitle()
 		),
 	] );
 } else {
 	Header::spawn( null, [
 		'title' => sprintf(
 			__( "Aggiungi %s" ),
 			__( "Evento" )
 		),
 	] );
 }
 
 ?>
 
 	<?php if( $warning ): ?>
 		<div class="card-panel yellow"><?= esc_html( $warning ) ?></div>
 	<?php endif ?>
 
 	<p><?= HTML::a(
 		$conference->getConferenceURL(),
 		esc_html( $conference->getConferenceTitle() ) . icon( 'home', 'left' )
 	) ?></p>
 
 	<?php if( $event && $event->hasEventPermalink() ): ?>
 		<p><?= HTML::a(
 			// href
 			$event->getEventURL(),
 
 			// text
 			__( "Vedi" ) . icon( 'account_box', 'left' )
 		) ?></p>
 	<?php endif ?>
 
 	<form method="post">
 		<?php form_action( 'save-event' ) ?>
 
 		<div class="row">
 
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="event-title"><?= __( "Titolo" ) ?></label>
 					<input type="text" name="title" id="event-title" required<?php
 						if( $event ) {
 							echo value( $event->get( Event::TITLE ) );
 						}
 					?> />
 				</div>
 			</div>
 
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="event-uid"><?= __( "Codice" ) ?></label>
 					<input type="text" name="uid" id="event-uid" required<?php
 						if( $event ) {
 							echo value( $event->get( Event::UID ) );
 						}
 					?> />
 				</div>
 			</div>
 
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="event-subtitle"><?= __( "Sottotitolo" ) ?></label>
 					<input type="text" name="subtitle" id="event-subtitle"<?php
 						if( $event ) {
 							echo value( $event->get( Event::SUBTITLE ) );
 						}
 					?> />
 				</div>
 			</div>
 
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="event-url"><?= __( "URL" ) ?></label>
 					<input type="text" name="url" id="event-url"<?php
 						if( $event ) {
 							echo value( $event->get( Event::EXTERNAL_URL ) );
 						}
 					?> />
 				</div>
 			</div>
 
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="event-language"><?= __( "Lingua" ) ?></label>
 					<input type="text" name="language" id="event-language" maxlenght="2"<?php
 						if( $event ) {
 							echo value( $event->get( Event::LANGUAGE ) );
 						}
 					?> />
 				</div>
 			</div>
 
 		</div>
 
 		<div class="row">
 
 			<!-- chapters -->
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="chapter"><?= __( "Capitolo" ) ?></label>
 					<select name="chapter">
 						<?php
 							// get every chapter
 							$chapters =
 								Chapter::factory()
 									->orderBy( Chapter::NAME )
 									->queryGenerator();
 
 							// generate select options
 							foreach( $chapters as $chapter ) {
 								$option = ( new HTML( 'option' ) )
 									->setText( esc_html( $chapter->getChapterName() ) )
 									->setAttr( 'value',  $chapter->getChapterID() );
 
 								// eventually select this chapter
 								$selected = false;
 
 								if( $event && $event->has( Chapter::ID ) ) {
 									$selected = $event->getChapterID() === $chapter->getChapterID();
 								} elseif( isset( $_GET['chapter'] ) ) {
 									$selected = $_GET['chapter'] === $chapter->getChapterUID();
 								}
 
 								if( $selected ) {
 										$option->setAttr( 'selected', 'selected' );
 								}
 
 								echo $option->render();
 							}
 						?>
 					</select>
 				</div>
 			</div>
 			<!-- /chapters -->
 
 			<!-- tracks -->
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="track"><?= __( "Traccia" ) ?></label>
 					<select name="track">
 						<?php
 							// select all the available tracks for this Location
 							$tracks =
 								Track::factory()
 									->orderBy( Track::NAME )
 									->queryGenerator();
 
 							// generate a select option for each track
 							foreach( $tracks as $track ) {
 								$option = ( new HTML( 'option' ) )
 									->setText( esc_html( $track->getTrackName() ) )
 									->setAttr( 'value', $track->getTrackID() );
 
 								// eventually auto-select this track
 								$selected = false;
 								if( $event && $event->has( Track::ID ) ) {
 									$selected = $event->getTrackID() === $track->getTrackID();
 								} elseif( isset( $_GET['track'] ) ) {
 									$selected = $_GET['track'] === $track->getTrackUID();
 								}
 
 								if( $selected ) {
 										$option->setAttr( 'selected', 'selected' );
 								}
 
 								echo $option->render();
 							}
 						?>
 					</select>
 				</div>
 			</div>
 			<!-- /tracks -->
 
 			<!-- rooms -->
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="room"><?= __( "Stanza" ) ?></label>
 					<select name="room">
 						<?php
 							// select all the available rooms for this Location
 							$rooms =
 								Room::factory()
 									->whereInt( Location::ID, $conference->getLocationID() )
 									->orderBy( Room::NAME )
 									->queryGenerator();
 
 							// generate a select option for each room
 							foreach( $rooms as $room ) {
 								$option = ( new HTML( 'option' ) )
 									->setText( esc_html( $room->getRoomName() ) )
 									->setAttr( 'value', $room->getRoomID() );
 
 								// eventually auto-select this room
 								$selected = false;
 								if( $event && $event->has( Room::ID ) ) {
 									$selected = $event->getRoomID() === $room->getRoomID();
 								} elseif( isset( $_GET['room'] ) ) {
 									$selected = $_GET['room'] === $room->getRoomUID();
 								}
 
 								if( $selected ) {
 										$option->setAttr( 'selected', 'selected' );
 								}
 
 								echo $option->render();
 							}
 						?>
 					</select>
 				</div>
 			</div>
 			<!-- /rooms -->
 
 		</div>
 
 
 		<div class="row">
 
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="event-start"><?= __( "Inizio" ) ?></label>
 					<input type="text" name="start" required placeholder="Y-m-d H:i:s"<?php
 						if( $event ) {
 							echo value( $event->getEventStart()->format( 'Y-m-d H:i:s' ) );
 						} elseif( isset( $_GET['start'] ) ) {
 							echo value( $_GET['start'] );
 						}
 					?> />
 				</div>
 			</div>
 
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="event-end"><?= __( "Fine" ) ?></label>
 					<input type="text" name="end" required placeholder="Y-m-d H:i:s"<?php
 						if( $event ) {
 							echo value( $event->getEventEnd()->format( 'Y-m-d H:i:s' ) );
 						} elseif( isset( $_GET['end'] ) ) {
 							echo value( $_GET['end'] );
 						}
 					?> />
 				</div>
 			</div>
 
 			<div class="col s12 m4 l3">
 				<div class="card-panel">
 					<label for="event-aborted"><?= __( "Annullato" ) ?></label>
 					<select name="aborted">
 						<option value="0"<?= selected( !$event || !$event->isEventAborted() ) ?>><?= __( "No"  ) ?></option>
 						<option value="1"<?= selected(  $event && $event->isEventAborted() ) ?>><?= __( "Sì" ) ?></option>
 					</select>
 				</div>
 			</div>
 
 			<div class="col s12">
 				<p><button type="submit" class="btn waves-effect"><?= __( "Salva" ) ?></button></p>
 			</div>
 
 		</div>
 
 		<?php foreach( Event::fields_i18n() as $i18n_column => $label ): ?>
 			<h3><?= $label ?></h3>
 			<div class="row">
 				<?php foreach( all_languages() as $lang ): ?>
 					<?php $iso = $lang->getISO() ?>
 					<?php $field = $i18n_column . '_' . $iso ?>
 					<div class="col s12 m6">
 						<div class="card-panel">
 							<label for="event-abstract"><?= $label ?> (<?= $lang->getHuman() ?>)</label>
 							<textarea name="<?= esc_attr( $field ) ?>" class="materialize-textarea"><?php
 								if( $event ) {
 									echo esc_html( $event->get( $field ) );
 								}
 							?></textarea>
 						</div>
 					</div>
 				<?php endforeach ?>
 			</div>
 		<?php endforeach ?>
 
 		<!-- Image -->
 		<div class="row">
 			<div class="col s12 m6">
 				<div class="card-panel">
 					<label for="event-image"><?= __( "Immagine" ) ?></label>
 					<input type="text" name="image"<?php
 						if( $event ) {
 							echo value( $event->get( Event::IMAGE ) );
 						}
 					?>/ >
 					<?php if( $event && $event->hasEventImage() ): ?>
 						<img src="<?= esc_attr( $event->getEventImage() ) ?>" class="responsive-img" alt="<?= esc_attr( $event->getEventTitle() ) ?>" />
 					<?php endif ?>
 				</div>
 			</div>
 		</div>
 		<!-- /Image -->
 
 		<div class="row">
 			<div class="col s12">
 				<button type="submit" class="btn waves-effect"><?= __( "Salva" ) ?></button>
 			</div>
 		</div>
 	</form>
 
 	<!-- image -->
 	<?php if( $event ): ?>
 		<form method="post" enctype="multipart/form-data">
 			<?php form_action( 'change-image' ) ?>
 			<div class="row">
 				<div class="col s12">
 					<div class="card-panel">
 
 						<h3><?= __( "Nuova Immagine" ) ?></h3>
 
 						<div class="file-field input-field">
 							<div class="btn">
 								<span><?= __( "Sfoglia" ) ?></span>
 								<input name="image" type="file" />
 							</div>
 							<div class="file-path-wrapper">
 								<input class="file-path validate" type="text" />
 							</div>
 						</div>
 						<button type="submit" class="btn waves-effect"><?= __( "Carica" ) ?></button>
 					</div>
 				</div>
 			</div>
 		</form>
 	<?php endif ?>
 	<!-- /image -->
 
 	<?php if( $event ): ?>
 	<div class="row">
 		<div class="col s12 m6">
 			<div class="card-panel">
 				<h3><?php printf(
 					__( "Associa %s" ),
 					__( "Utente" )
 				) ?></h3>
 				<form action="" method="post">
 					<?php form_action( 'add-user' ) ?>
 					<select name="user" class="browser-default">
-						<?php $users = User::factory()
+						<?php $all_users = User::factory()
 							->select( [
 								User::UID,
 								User::NAME,
 								User::SURNAME,
 							] )
 							->orderBy( User::NAME )
 							->queryGenerator();
 						?>
-						<?php foreach( $users as $user ): ?>
+						<?php foreach( $all_users as $user ): ?>
 							<option value="<?= $user->getUserUID() ?>">
 								<?= esc_html( $user->getUserFullname() ) ?>
 							</option>
 						<?php endforeach ?>
 					</select>
 					<p><button type="submit" class="btn"><?= __("Aggiungi") ?></button></p>
 				</form>
 
 				<p><?= HTML::a(
 					User::editURL(),
 					sprintf(
 						__( "Aggiungi %s" ),
 						sprintf(
 							__( "Nuovo %s" ),
 							__( "Utente" )
 						)
 					)
 				) ?></p>
 			</div>
 		</div>
 	</div>
 	<?php endif ?>
 
 	<?php if( $event ): ?>
-		<?php $users = $event->factoryUserByEvent()
-			->select( [
-				User::UID,
-				EventUser::ORDER,
-				EventUser::ROLE,
-			] )
-			->defaultClass( EventUser::class )
-			->orderBy( EventUser::ORDER )
-			->queryGenerator();
-		?>
 
-		<?php if( $users->valid() ): ?>
+		<?php if( $users ): ?>
 			<h3><?php printf(
 				__( "Modifica %s" ),
 				__( "Ordinamento" )
 			) ?></h3>
 			<div class="row">
 				<?php foreach( $users as $i => $user ): ?>
 					<div class="col s12 m6">
 						<div class="card-panel">
 							<div class="row">
 							<form action="" method="post">
 								<?php form_action( 'update-user' ) ?>
 								<div class="col s12 m6">
 									<input type="text" name="user"<?= value( $user->getUserUID() ) ?> />
 								</div>
 								<div class="col s12 m6">
 									<input type="number" name="order"<?= value( $user->getEventUserOrder() ) ?>" />
 								</div>
 								<div class="col s12 m6">
 									<select name="role">
 										<?php foreach( EventUser::roles() as $role ): ?>
 											<option<?=
 												value( $role ) .
 												selected( $role === $user->getEventUserRole() )
 											?>><?= esc_html( $role ) ?></option>
 										<?php endforeach ?>
 									</select>
 								</div>
 								<div class="col s12 m6">
 									<input type="checkbox" name="delete" value="yes" id="asd-<?= $i ?>" />
 									<label for="asd-<?= $i ?>"><?= __("Elimina") ?></label>
 								</div>
 								<div class="col s12 m6">
 									<p><button type="submit" class="btn"><?= __("Salva") ?></button></p>
 									<p><small><?= HTML::a(
 										$user->getUserEditURL(),
 										sprintf(
 											__( "Modifica %s" ),
 											__( "Utente" )
 										)
 									) ?></small></p>
 								</div>
 							</form>
 							</div>
 						</div>
 					</div>
 				<?php endforeach ?>
 			</div>
 		<?php endif ?>
 	<?php endif ?>
 
 	<!-- start Sharables -->
 	<?php if( $event && $sharables ): ?>
 
 		<h3><?= __( "Materiali condivisi" ) ?></h3>
 
 		<ul class="collection">
 
 			<?php foreach( $sharables as $sharable ): ?>
 				<li class="collection-item"><?= HTML::a(
 					$sharable->getSharableEditURL(),
 					esc_html( $sharable->getSharableTitle() )
 				) ?></li>
 			<?php endforeach ?>
 
 			<!-- start add Sharable -->
 			<li><?= HTML::a(
 				Sharable::editURL( [
 					'event_ID' => $event->getEventID(),
 				]  ),
 				__( "Aggiungi" )
 			) ?></li>
 			<!-- end add Sharable -->
 
 		</ul>
 
 	<?php endif ?>
 	<!-- end Sharables -->
+
+	<!-- start FFmpeg parameters -->
+	<?php if( $event ): ?>
+
+		<p><?= __( "Command to set video metadata with ffmpeg:" ) ?></p>
+		<textarea><?= esc_html( VideoMetadata::command( [
+			'conference' => $conference,
+			'event'      => $event,
+			'users'      => $users,
+			'input'      => 'video.mp4',
+			'metadata'   => [
+				'license' => 'CC BY SA 4.0',
+			],
+		] ) ) ?></textarea>
+
+	<?php endif ?>
+	<!-- end FFmpeg parameters -->
 <?php
 
 Footer::spawn();
diff --git a/includes/class-VideoMetadata.php b/includes/class-VideoMetadata.php
new file mode 100644
index 0000000..3436735
--- /dev/null
+++ b/includes/class-VideoMetadata.php
@@ -0,0 +1,157 @@
+<?php
+# Suckless Conference
+# Copyright (C) 2020 Valerio Bozzolan
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// default FFMPEG command pathname
+define_default( 'FFMPEG_COMMAND', 'ffmpeg' );
+
+/**
+ * Tool to save video metadata with FFMPEG
+ *
+ * @See https://wiki.multimedia.cx/index.php?title=FFmpeg_Metadata
+ */
+class VideoMetadata {
+
+	/**
+	 * Print an FFMPEG command
+	 *
+	 * To see some available metadatas:
+	 *   https://wiki.multimedia.cx/index.php?title=FFmpeg_Metadata
+	 *
+	 * @param array $args Associative array of arguments
+	 *  Some available keys:
+	 *   'input'    => (string)   Input file path
+	 *   'output'   => (string)   Output file path
+	 *   'metadata' => (array)    Associative array of metadata
+	 *      Some of them:
+	 *        title
+	 *        author
+	 *        album_artist
+	 *        album
+	 *        composer
+	 *        year
+	 *        copyright
+	 *        description
+	 *        language
+	 *
+	 * @param array $data Arguments
+	 */
+	public static function command( $data = [] ) {
+
+		$args = [];
+
+		// print the input file '-i stuff'
+		if( !empty( $data['input'] ) ) {
+			$args[] = escapeshellarg( '-i' );
+			$args[] = escapeshellarg( $data['input'] );
+		}
+
+		// default arguments
+		$data['metadata'] = $data['metadata']   ?? [];
+		$event            = $data['event']      ?? null;
+		$conference       = $data['conference'] ?? null;
+
+		// inherit some Event parameters
+		if( $event ) {
+
+			// enrich the Metadata with some Event stuff
+			$data['metadata'] = array_replace( [
+				'title'    => $event->getEventTitle(),
+				'language' => $event->getEventLanguage(),
+				'date'     => $event->getEventStart( 'Y' ),
+			], $data['metadata'] );
+		}
+
+		// inherit some Conference parameters
+		if( $conference ) {
+			$data['metadata'] = array_replace( [
+				'album' => $conference->getConferenceTitle(),
+			], $data['metadata'] );
+		}
+
+		// eventually generate some credits
+		if( empty( $data['metadata']['author'] ) && isset( $data['users'] ) ) {
+			$data['metadata']['author'] = self::generateUserCredits( $data['users'] );
+		}
+
+		// loop metadata and build arguments
+		foreach( $data['metadata'] as $key => $value ) {
+
+			// build pairs of '-metadata stuff=foo'
+			$args[] = escapeshellarg( '-metadata' );
+			$args[] = escapeshellarg( sprintf(
+				"%s=%s",
+				$key,
+				$value
+			) );
+		}
+
+		// print the output file 'stuff'
+		// the default is "input.with_metadata"
+		$output = $data['output'] ?? $data['input'] . '.with_metadata';
+		if( !empty( $data['output'] ) ) {
+			$args[] = escapeshellarg( $data['output'] );
+		}
+
+		// merge the arguments
+		$args_complete = implode( ' ', $args );
+
+		// return the complete command
+		return sprintf(
+			"%s %s",
+			escapeshellcmd( FFMPEG_COMMAND ),
+			$args_complete
+		);
+	}
+
+	/**
+	 * Generate some user credits
+	 *
+	 * @param EventUser[] $users
+	 * @return string
+	 */
+	public static function generateUserCredits( $users ) {
+
+		// users indexed by role
+		$grouped = [
+			'speaker'   => [],
+			'moderator' => [],
+		];
+		foreach( $users as $user ) {
+			$role = $user->get( EventUser::ROLE );
+
+			// eventually create empty and then append
+			$grouped[ $role ] = $grouped[ $role ] ?? [];
+			$grouped[ $role ][] = $user->getUserDisplayName();
+		}
+
+		$lines = [];
+
+		$speakers   = implode( ', ', $grouped['speaker'] );
+		$moderators = implode( ', ', $grouped['moderator'] );
+
+		if( $speakers ) {
+			$lines[] = sprintf( __( "Relatori: %s" ), $speakers );
+		}
+
+		if( $moderators ) {
+			$lines[] = sprintf( __( "Moderatori: %s" ), $moderators );
+		}
+
+		return implode( "\n", $lines );
+	}
+}
+