OBS Lua script that checks the contents of a file and sets a media source's local_source if the content changed.

VideoFileFromText.lua

-- -------------------------------------------------------------
-- Load Video File from Text
-- 
-- Loads media from the contents of a given input text file.
-- Intended to be used with the StreamDeck.
-- -------------------------------------------------------------

obs = obslua

p_TimerId          = 0

p_VideoFile        = nil
p_CurrentSceneName = nil
p_CurrentVideoFile = nil
p_LockOut          = false

p_VideoFileList    = nil
p_SourceName       = nil
p_SceneName        = nil
p_Enabled          = true
p_Interval         = 100

--- ------------------------------------------------------------
--- Script Metadata
--- ------------------------------------------------------------

function script_description()
    return [[Reads the path of a video file from a selected text file and updates a selected media source using the new video file path. It reads the text file for changes at preditermined intervals.]]
end

function script_load()

end

function script_unload()

end

--- ------------------------------------------------------------
--- Primary Script Functions
--- ------------------------------------------------------------

function init()
    -- increase the timer id - old timers will be cancelled
    p_TimerId = p_TimerId + 1

    -- only proceed if there is a text file selected
    if not p_VideoFileList
      or not p_SourceName
      or not p_SceneName
      or not p_Enabled then
        return nil
    end

    -- start the timer to check the text file
    local id = p_TimerId
    obs.timer_add(function() check_txt_file(id) end, p_Interval)
end

function file_exists(filename)
    local f = io.open(filename, "rb")

    if f then
        f:close()
    end

    return f ~= nil
end

function read_txt_file(filename)
    filename = filename or ''
    
    local line
    local videoFile

    if not file_exists(filename) then
        return
    end

    for line in io.lines(filename) do

        if line ~= "" then
            videoFile = line

            if p_CurrentVideoFile == videoFile then
                print("Video file has not changed")
                return
            else
                p_CurrentVideoFile = videoFile
                set_media_source_file(videoFile)
                return
            end
        end
    end
end

function set_media_source_file(filename)
    local source = obs.obs_get_source_by_name(p_SourceName)
    
    if source ~= nil then
        local settings = obs.obs_data_create()
        obs.obs_data_set_string(settings, "local_file", filename)
        obs.obs_source_update(source, settings)
        obs.obs_data_release(settings)
    end
    
    obs.obs_source_release(source)
    
    print("Updated local_file for source \"" .. p_SourceName .. "\" to \"" .. filename .. "\"")
end

function get_current_scene_name()
    local currentScene     = obs.obs_frontend_get_current_scene()
    local currentSceneName = obs.obs_source_get_name(currentScene)
    
    obs.obs_source_release(currentScene)
    p_LockOut          = p_CurrentSceneName == currentSceneName
    p_CurrentSceneName = currentSceneName

    return currentSceneName
end

function check_txt_file(timerId)
    if timerId < p_TimerId then
        obs.remove_current_callback()
        return
    end

    if p_Enabled then
        if get_current_scene_name() == p_SceneName then    
            if not p_LockOut then
                read_txt_file(p_VideoFileList)
            end
        end
    end
end

--- -------------------------------------------------------------------------
--- Script Properties
--- -------------------------------------------------------------------------

function script_defaults(s)
    obs.obs_data_set_default_bool(s, "p_Enable", false)
    obs.obs_data_set_default_int(s, "p_Interval", 100)
end

function script_update(s)
    p_VideoFileList = obs.obs_data_get_string(s, "p_VideoFileList")
    p_SourceName    = obs.obs_data_get_string(s, "p_TargetSource")
    p_SceneName     = obs.obs_data_get_string(s, "p_SceneToCheck")
    p_Interval      = obs.obs_data_get_int(s, "p_Interval")
    p_Enabled       = obs.obs_data_get_bool(s, "p_Enable")
    init()
end

function script_properties()
    local p = obs.obs_properties_create()

    --- Enable checkbox
    obs.obs_properties_add_bool(p, "p_Enable", "Enable script")
    
    --- Interval input
    obs.obs_properties_add_int(p, "p_Interval", "Interval (ms)", 50, 20000, 10)

    --- Video File List input
    obs.obs_properties_add_path(p, "p_VideoFileList", "Video File List",
        obs.OBS_PATH_FILE,
        "Video File List (*.txt)",
        nil
    )
    
    --- Target Scene
    local s = obs.obs_properties_add_list(p, "p_SceneToCheck", "Scene", obs.OBS_COMBO_TYPE_EDITABLE, obs.OBS_COMBO_FORMAT_STRING)
    local scenes = obs.obs_frontend_get_scenes()
    if scenes ~= nil then
        for _, scene in ipairs(scenes) do
            scene_id = obs.obs_source_get_id(scene)
            local sceneName = obs.obs_source_get_name(scene)
            obs.obs_property_list_add_string(s, sceneName, sceneName)
        end
    end

    --- Target Media Source
    local t = obs.obs_properties_add_list(p, "p_TargetSource", "Media Source", obs.OBS_COMBO_TYPE_EDITABLE, obs.OBS_COMBO_FORMAT_STRING)
    local sources = obs.obs_enum_sources()
    if sources ~= nil then
        for _, source in ipairs(sources) do
            source_id = obs.obs_source_get_id(source)
            if source_id == "ffmpeg_source" then
                local sourceName = obs.obs_source_get_name(source)
                obs.obs_property_list_add_string(t, sourceName, sourceName)
            end
        end
    end
    obs.source_list_release(sources)

    return p
end