mfx/lib/container/webM/WebMContainerDecoder.ts

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

import JsWebm from "jswebm";
import { ContainerDecoder } from "../ContainerDecoder";
import { type AudioTrack, TrackType, type VideoTrack } from "../Track";
import { next } from "../../utils";

/**
 * @group Decode
 */
export class WebMContainerDecoder extends ContainerDecoder<any> {
  get identifier() {
    return "WebMContainerDecoder";
  }

  constructor({ videoCodec = "vp8", audioCodec = "" }) {
    const demuxer = new JsWebm();

    super({
      transform: async (chunk) => {
        demuxer.queueData(chunk.buffer);
      },
      flush: async () => {
        while (!demuxer.videoTrack && !demuxer.eof) {
          await demuxer.demux();
        }
        let videoCursor = 0;
        let audioCursor = 0;

        const { videoTrack, audioTrack } = demuxer;

        const processedVideoTrack: VideoTrack<any> | null = videoTrack
          ? {
              id: videoTrack.trackUID,
              type: TrackType.Video,
              duration: 0,
              config: {
                codec: videoCodec,
                codedHeight: videoTrack.height,
                codedWidth: videoTrack.width,
              },
              toChunk: (sample) =>
                new EncodedVideoChunk({
                  type: sample.isKeyframe ? "key" : "delta",
                  timestamp:
                    sample.timestamp * demuxer.segmentInfo.timecodeScale,
                  data: sample.data,
                  transfer: [sample.data],
                }),
            }
          : null;

        const processedAudioTrack: AudioTrack<any> | null = audioTrack
          ? {
              id: audioTrack.trackUID,
              type: TrackType.Audio,
              config: {
                codec: audioCodec || demuxer.audioCodec,
                numberOfChannels: audioTrack.channels,
                sampleRate: audioTrack.rate,
              },
              toChunk: (sample) =>
                new EncodedAudioChunk({
                  type: "key",
                  data: sample.data,
                  timestamp:
                    sample.timestamp * demuxer.segmentInfo.timecodeScale,
                }),
            }
          : null;

        const tracks = [
          /**
           * @note
           * Skip video if not available to support
           * audio only (m4a) files
           */
          ...(processedVideoTrack ? [processedVideoTrack] : []),
          ...(processedAudioTrack ? [processedAudioTrack] : []),
        ];

        this.start(tracks);

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

          if (!this.desiredSize) {
            await next(0);
            continue;
          }

          while (videoCursor < demuxer.videoPackets.length) {
            const packet = demuxer.videoPackets[videoCursor];

            if (videoCursor === 0) {
              packet.isKeyframe = true;
            }

            this.queue({
              track: processedVideoTrack,
              samples: [packet],
            });

            videoCursor++;
          }

          while (audioCursor < demuxer.audioPackets.length) {
            const packet = demuxer.audioPackets[audioCursor];

            this.queue({
              track: processedAudioTrack,
              samples: [packet],
            });

            audioCursor++;
          }
        }
      },
    });
  }
}