Remove the random number from the transcoded filename

functions.php

<?php
/**
 * Add this function to theme's functions.php
 * Remove the random number from the transcoded filename
 *
 * @param string $tempname Transcoded file's temporary name.
 * @return string $tempname Updated filename.
 */
function rtmc_transcoded_temp_filename( $tempname ) {
	if ( class_exists( 'RT_Transcoder_Admin' ) ) {

		// Divide the name from "-".
		$filename_arr = explode( '-',  $tempname );
		// Gets the removable part from filename.
		$start_pos = strlen( $filename_arr[0] );
		// Removes the number from filename.
		$tempname = substr( $tempname, $start_pos + 1 );
	}
	return $tempname;
}
add_filter( 'transcoded_temp_filename', 'rtmc_transcoded_temp_filename' );

Replace this line
https://github.com/rtMediaWP/transcoder/blob/master/admin/rt-transcoder-handler.php#L723

with

$thumbinfo['basename'] = apply_filters( 'transcoded_temp_filename', $temp_name );