Examples for converting sample/bitrate?

[faxinadu]

Hey,

I would really like to see an example of converting a file's bit depth and sample rate, I have been trying to get this to work but can not, would it be possible to see some simple Lua code to demonstrate?

[MasterVitronic]

I'm not sure if this is what you want, to be more precise, how would you do it from the command line with sox, here an example to modify the samplerate:

local libsox	= require("libsox")
local sox		= libsox:new()
local effect		= nil
local sample_rate 	= 22050/2 		-- New sample rate
local sound_input	= '/tmp/coco.mp3' 	-- Input sound
local sound_output	= '/tmp/coco2.mp3' 	-- Output sound


--All libSoX applications must start by initialising the SoX library
if not sox:init() then
	error("Failed to initialize SoX")
end

--Open audiofile
local input = sox:open_read(sound_input)
if not input then
	error("Failed to open input handler")
end
local in_signal = sox:signal(input)

--Open soundcard
--Change "alsa" in this line to use an alternative audio device driver:
local output = sox:open_write('default', {
	rate=sample_rate,channels=2,precision=16
}, 'alsa')

--Write output file
--local output = sox:open_write(sound_output,{
	--rate=sample_rate,channels=2,precision=16
--}, 'mp3')

if not output then
	error("Failed to open output handler")
end
local out_signal = sox:signal(output)

--Create an effects chain; some effects need to know about the input
--or output file encoding so we provide that information here
local chain = sox:create_effects_chain(input, output)

local interm_signal = input  -- NB: deep copy

effect = sox:create_effect(sox:find_effect("input"))
	assert(sox:effect_options(effect, 1, input))
	assert(sox:add_effect(chain, effect, input, input))
effect = nil

effect = sox:create_effect(sox:find_effect("rate"))
	assert(sox:effect_options(effect, 1, sample_rate))
	assert(sox:add_effect(chain, effect, interm_signal, input))
effect = nil

effect = sox:create_effect(sox:find_effect("output"))
	assert(sox:effect_options(effect, 1, output))
	assert(sox:add_effect(chain, effect, input, input))
effect = nil

--Flow samples through the effects processing chain until EOF is reached
sox:flow_effects(chain)

--All done; tidy up:
sox:delete_effects_chain(chain)
sox:close(input)
sox:close(output)
sox:quit()

[faxinadu]

Hey, thanks for your reply.

If I follow along your example, I get incorrect results.

I have built my function like this:

function CtSox.sox_convert_samplerate(input_file,output_file,encoder,sample_rate,verbose_mode)
    if verbose_mode == nil then verbose_mode = true end
    if verbose_mode then print("----------SoX Audio Process----------") end

    if sample_rate == nil then sample_rate = 44100 end
    if encoder == nil then encoder = "wav" end
    if output_file == nil then output_file = filesystem.replaceExtension(input_file,encoder) end

    local input = sox:open_read(input_file)
    local in_signal = sox:signal(input)
    
    local output = sox:open_write(output_file,{rate=sample_rate,channels=2,precision=16},encoder)
    
    local out_signal = sox:signal(output)
    
    local chain = sox:create_effects_chain(input, output)
    local effect

    local interm_signal = input  -- NB: deep copy
    
    effect = sox:create_effect(sox:find_effect("input"))
    sox:effect_options(effect,1,input)
    sox:add_effect(chain,effect,input, input)
    
    effect = sox:create_effect(sox:find_effect("rate"))
    sox:effect_options(effect,1,sample_rate)
    sox:add_effect(chain,effect,interm_signal,input)
    
    effect = sox:create_effect(sox:find_effect("output"))
    sox:effect_options(effect,1,output)
    sox:add_effect(chain,effect,input,input)
    
    sox:flow_effects(chain)
    
    sox:delete_effects_chain(chain)
    sox:close(input)
    sox:close(output)
end

I call it like this:

local process_sample_rates = {
    "48000",
    "44100",
    "22050"
}

if run_sr_tests then
    for i = 1,#process_sample_rates, 1 do
        local output_file = directory_path .. "/" .. filesystem.stem(file) .. "_sr_test_" .. process_sample_rates[i] .. ".wav"
        ctSox.sox_convert_samplerate(file,output_file,"wav",process_sample_rates[i],verbose_mode)
    end
end

The resulting files I get are wrong, as shown in their infos:

Any ideas what is wrong here?