Add Transcoder

[twlite]

Since this library was created for discord-player, the API should be similar to its current transcoder, which is a node.js stream. It works by taking raw stream, piping it to transcoder and receive the desired output.

My current idea is to implement something similar to the following:

import { probeStream, CodecType, Transcoder } from 'mediaplex'

const stream = getInputStream();
const probeResult = await probeStream(stream);

if (!probeResult.result) return; // unsupported stream

const transcoder = new Transcoder({
    format: CodecType.OPUS, // the output format
    sampleRate: 48000, // output sample rate
    channels: 2, // the number of channels
    ... // other options
}); // Transcoder extends Transform stream

const output = stream.pipe(transcoder); // output shall be Opus stream, as specified in format