vt-transcode-worker's Introduction

vt-transcode-worker

A video transcoder service, which prepares the video for streaming using HLS.
Transcode worker will transcode the videos into multiple renditions using ffmpeg, creates the HLS manifest and uploads it to S3 or any other object store.

Request message format

export interface TranscodeWorkerInput {
  requestId: string;
  inputFile: RemoteFile;
  transcodeConfig: TranscodeConfig;
}

RemoteFile

Details of the input video stored in a remote location

export interface RemoteFile {
  requestId: string;
  contentLength?: number;
  contentSha1?: string;
  contentType?: string;
  fileId: string;
  fileName: string;
  uploadTimestamp?: number;
}

TranscodeConfig

The configuration for ffmpeg for transcoding the asset.

export interface TranscodeConfig {
  renditions: Rendition[];
  /**
   * Presets affect the encoding speed.
   * Using a slower preset gives you better compression, or quality per filesize,
   * whereas faster presets give you worse compression
   * @default 'veryfast'
   */
  preset: FFmpegPreset | string;
  /**
   *@default 'libx264'
   */
  videoCodec: string;
  /**
   * @default 'aac'
   */
  audioCodec: string;
  /**
   * Segment size in seconds
   * @default 6
   */
  segmentDuration: number;
}

export enum FFmpegPreset {
  UltraFast = "ultrafast",
  SuperFast = "superfast",
  VeryFast = "veryfast",
  Faster = "faster",
  Fast = "fast",
  Medium = "medium",
  Slow = "slow",
  Slower = "slower",
  verySlow = "veryslow",
}

export interface Rendition {
  resolution: {
    width: number;
    height: number;
  };
  videoBitRate: number;
  audioBitRate: number;
}

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vt-transcode-worker's Issues

Implement Split-transcode-merge

In order to improve the performance of transcoding, try splitting the input video into chunks, distribute the video to multiple nodes for transcoding, gather all the chunks and combine to create the final video.

Add subtitle support

Create webVTT subtitle from the provided source subtitle (eg: srt)

Try better codec to improve streaming quality

Currently, video tom uses h.264 codec. Which is hugely popular and widely supported.
But to cope with the lower performance of cloudflare and backblaze B2, a better codec is required.
H.265 (or HEVC) is a potential alternative, it provides same video quality at half the bitrate. But, HEVC is not widely adopted due to heavy license fees. Very less support for hardware-accelerated encoding/decoding.
AV1 and VP9 are 2 different alternatives. VP9 is a promising codec, and its already being used by Youtube, Netflix and may others.
Need to check about VP9 support for HLS. I don't want to go in the HEVC path, so if required we can switch to Mpeg-Dash from HLS.

Todo: