mfx/lib/container/webM/WebMContainerProbe.ts

In-browser video editing toolkit, with effects accelerated by WebGL

import JsWebm from "jswebm";
import { next } from "../../utils";
import { vp9 } from "../../codec/vp9";
import { MFXWritableStream } from "../../stream";

/**
 * Probes codec information about a WebM container
 * @group Decode
 */
export class WebMContainerProbe extends MFXWritableStream<Uint8Array> {
  get identifier() {
    return "WebMContainerProbe";
  }

  // Returns codec string after container is fully processed
  async getCodec(): Promise<string> {
    return new Promise((resolve, reject) => {
      this.addEventListener("codec", (ev: CustomEvent) =>
        resolve(ev.detail.codec as string),
      );

      this.addEventListener("error", (ev: CustomEvent) =>
        reject(ev.detail.error as string),
      );
    });
  }

  constructor() {
    const demuxer = new JsWebm();

    super(
      {
        write: async (chunk) => {
          demuxer.queueData(chunk.buffer);
        },
        close: async () => {
          let idx = 0;
          let size = 0;

          while (!demuxer.eof) {
            await demuxer.demux();
            await next(0);

            while (idx < demuxer.videoPackets.length) {
              const packet = demuxer.videoPackets[idx];
              size += packet.data.byteLength;
              idx++;
            }
          }

          this.dispatchEvent(
            new CustomEvent("codec", {
              detail: {
                codec: {
                  V_VP9: vp9.autoSelectCodec({
                    width: demuxer.videoTrack.width,
                    height: demuxer.videoTrack.height,
                    bitDepth: 8, // TODO: calculate bit depth
                    bitrate: (size * 8) / demuxer?.duration, // Bitrate is assigned after all video tracks are read
                  }),
                  V_VP8: "vp8",
                }[demuxer.videoTrack.codecID],
                codedHeight: demuxer.videoTrack.height,
                codedWidth: demuxer.videoTrack.width,
              },
            }),
          );
        },
      },
      new CountQueuingStrategy({
        highWaterMark: Infinity,
      }),
    );
  }
}