The byteLength read-only property of the EncodedVideoChunk interface returns the length in bytes of the encoded video data.

An integer.

In the following example the byteLength is printed to the console.

const init = {
  type: "key",
  data: videoBuffer,
  timestamp: 23000000,
  duration: 2000000,
};
chunk = EncodedVideoChunk(init);

console.log(chunk.byteLength); //352800