libltc wrapper

This module gives you access to the libltc library from node.js.

Bits per sample

Internally libltc uses 8 bit unsigned audio data, but the decoder supports reading uint16, sint16 and float too. The encoder however only supports uint8.

Installation

The following architectures are supported:

• linux-x64
• linux-armhf
• linux-arm64
• macos-x64
• macos-arm64 (M1)
• windows-x64

Add the module to your project:

npm i libltc-wrapper
# or
yarn add libltc-wrapper

State

• Successfully encodes and decodes LTC audio
• Tested successfully on Macbook Pro M1 (arm64) and Ubuntu 20.04 (x64)

Examples

Decoding

    const { LTCDecoder } = require('libltc-wrapper');
    const decoder = new LTCDecoder(48000, 25, "u8"); // 48khz, 25 fps, unsigned 8 bit

    // Write audio buffer to the decoder
    decoder.write(audioframes);

    // Check if there is any ltc frames ready
    let frame = decoder.read();

    if (frame !== undefined) {
        // found a valid frame
        console.log("Frame: ", frame);
    }

Encoding

    const { LTCEncoder, LTC_USE_DATE } = require('libltc-wrapper');

    const encoder = new LTCEncoder(48000, 25, LTC_USE_DATE); // 48khz, 25 fps, LTC_USE_DATE flag
    
    let time = new Date();

    encoder.setTimecode({
      hours: time.getHours(),
      minutes: time.getMinutes(),
      seconds: time.getSeconds(),
      frame: time.getMilliseconds() / (1000 / 25),
      days: time.getDate(),
      months: time.getMonth() + 1,
      years: time.getFullYear() % 100,
      timezone: "+0000"
    })

    // Every frame (25 times per second) increase the current frame
    encoder.incrementTimecode();

    // Get 1 frame worth of LTC audio (48khz 25fps would be 40ms audio)
    let buffer = encoder.getBuffer();

Class methods

LTCDecoder instance methods

constructor(sampleRate: number, framerate: number, audioFormat: string)

Samplerate in hz, for example 48000. Framerate should be less than or equal to 30 fps. Audioformat must be one of u8 for unsigned 8 bit, u16 for unsigned 16 bit, s16 for signed 16 bit, or float for 32 bit float.

write(buffer: Buffer)

Write audio data to the decoder, should be full frames, but any number of frames. They will be buffered up until it finds a LTC frame

read()

Reads the next frame from the decoder queue. If there are no frames in the queue it returns undefined. When a valid frame is found, it returns a LTCFrame object.

LTCEncoder instance methods

constructor(sampleRate: number, framerate: number, flags?: number);

Samplerate in hz, for example 48000. Framerate should be less than or equal to 30. Flags should be one, or a combination of the following flags: LTC_USE_DATE, LTC_TC_CLOCK, LTC_BGF_DONT_TOUCH, LTC_NO_PARITY. See the librtc documentation for more information about the flags. The default flag is LTC_USE_DATE.

setVolume(dBFS: number)

Set the volume of the generated LTC signal, in dBFs

setFilter(riseTime: number)

Set encoder signal rise-time / signal filtering, in uS. Default is 40.

setTimecode(timecode: LTCTimecode)

Set encoder timecode, expects a LTCTimecode object. You only need to specify non-zero parameters. The default is 0 for any omitted object parameters.

getTimecode()

Get the current encoder timecode. Returns a LTCTimecode object with the current position.

encodeFrame()

Write the next frame to the audio buffer. Fetch the buffer using getBuffer().

incrementTimecode()

Increment the current timecode by one frame.

decrementTimecode()

Decrement the timecode by one frame

getBuffer()

Returns the audio buffer for the current frame. The size of this buffer would be sample_rate / fps. So at 48000 khz, 25fps, that would be 1920 bytes of unsigned 8 bit audio.

License

This node module is licensed under the MIT license. And libltc is licensed under the GNU LGPL 3 license, but is included in this project in binary form and dynamically linked. So this module should in theory be safe to use in any open source or closed source commercial products. I am not a lawyer. This must not be construed as legal advice. Read more here http://answers.google.com/answers/threadview/id/439136.html