audio volume level. RIP source_volume_level

audio_level.lua

local obs = obslua
local ffi = require 'ffi'
local jit = require 'jit'
local obsffi
if ffi.os == "OSX" then
  obsffi = ffi.load("obs.0.dylib")
else
  obsffi = ffi.load("obs")
end

ffi.cdef[[
typedef struct obs_source obs_source_t;
obs_source_t *obs_get_source_by_name(const char *name);
void obs_source_release(obs_source_t *source);

enum obs_fader_type {
	OBS_FADER_CUBIC,
	OBS_FADER_IEC,
	OBS_FADER_LOG
};

typedef struct obs_volmeter obs_volmeter_t;

bool obs_volmeter_attach_source(obs_volmeter_t *volmeter,
				       obs_source_t *source);

int MAX_AUDIO_CHANNELS;

obs_volmeter_t *obs_volmeter_create(enum obs_fader_type type);

typedef void (*obs_volmeter_updated_t)(
	void *param, const float magnitude[MAX_AUDIO_CHANNELS],
	const float peak[MAX_AUDIO_CHANNELS],
	const float input_peak[MAX_AUDIO_CHANNELS]);

void obs_volmeter_add_callback(obs_volmeter_t *volmeter,
				      obs_volmeter_updated_t callback,
				      void *param);
]]

local lvl -- (1)
function callback_meter(data,mag,peak,input)
  lvl = 'Volume lvl is :' .. tostring(tonumber(peak[0]))
end
jit.off(callback_meter) -- (2)

function volume_lvl() -- (3)
  if lvl == nil then print('error lvl is nil') else print(lvl) end
end

function launch_callback() -- (4)
  local source = obsffi.obs_get_source_by_name("audio")
  local volmeter = obsffi.obs_volmeter_create(obsffi.OBS_FADER_LOG)
  -- https://github.com/WarmUpTill/SceneSwitcher/blob/214821b69f5ade803a4919dc9386f6351583faca/src/switch-audio.cpp#L194-L207
  local cb = ffi.cast("obs_volmeter_updated_t",callback_meter)
  obsffi.obs_volmeter_add_callback(volmeter,cb,data)
  obsffi.obs_volmeter_attach_source(volmeter,source)

  obsffi.obs_source_release(source)
end

local lock
function htk_3_cb(pressed)
  if pressed then
    if not lock then 
      print('launching volmeter callback')
      launch_callback()
      lock = true
    end
  end
end

function htk_1_cb(pressed)
  if pressed then
    volume_lvl()
  end
end

function htk_2_cb(pressed)
  if pressed then
    print('press 1 to view volume level of source with name audio, 3 to start ')
  end
end

key_1 = '{"htk_1": [ { "key": "OBS_KEY_1" } ],'
key_3 = '"htk_3": [ { "key": "OBS_KEY_3" } ],'
key_2 = '"htk_2": [ { "key": "OBS_KEY_2" } ]}'
json_s = key_1 .. key_3 .. key_2
default_hotkeys = {
  {id='htk_1',des='lvl',callback=htk_1_cb},
  {id='htk_2',des='info',callback=htk_2_cb},
  {id='htk_3',des='launch' ,callback=htk_3_cb},
}

function script_load(settings)

  s = obs.obs_data_create_from_json(json_s)
  for _,v in pairs(default_hotkeys) do
    local a = obs.obs_data_get_array(s,v.id)
    h = obs.obs_hotkey_register_frontend(v.id,v.des,v.callback)
    obs.obs_hotkey_load(h,a)
    obs.obs_data_array_release(a)
  end
  obs.obs_data_release(s)
end

See details here https://obsproject.com/forum/threads/tips-and-tricks-for-lua-scripts.132256/#post-492998