Node.js class to encode a sequence of image files into VP9 WEBM video using FFmpeg.

images2video.js

/*
 * encode image sequence into WEBM video
 */
import {exec}  from 'child-process-promise';
import format  from 'string-template';
import fsAsync from 'file-async';
import shell   from 'shelljs';
import path    from 'path';
import os      from 'os';

/*
 * ffmpeg must be installed with libvpx support (specify
 * --with-libvpx when using Homebrew and --enable-libvpx
 * when building from source), and be on the system path
 */
const FFMPEG_BIN = shell.which('ffmpeg');
if (! FFMPEG_BIN) {
  throw new Error(`FFmpeg not found`);
}

const DEV_NULL    = /Windows/.test(os.type()) ? '\\\\.\\NUL' : '/dev/null'
    , FFMPEG_TEMP =  path.join(os.tmpdir(), 'ffmpeg2pass')
    , FFMPEG_LOG  =  FFMPEG_TEMP + '-0.log';

// ffmpeg VP9 encoding guide:
// http://wiki.webmproject.org/ffmpeg/vp9-encoding-guide

const FFMPEG_BASE  = FFMPEG_BIN  + `\
 -loglevel error -y -i {input} -r {rate}\
 -c:v libvpx-vp9 -pass {pass} -passlogfile ${FFMPEG_TEMP}\
 -b:v 0 -crf 55 -pix_fmt yuv420p -threads 8 -speed {speed}\
 -tile-columns 6 -frame-parallel 1`
    , FFMPEG_PASS1 = FFMPEG_BASE + `\
 -f webm {output}`
    , FFMPEG_PASS2 = FFMPEG_BASE + `\
 -auto-alt-ref 1 -lag-in-frames 25 {output}`
    , PASS1_SPEED  = 4
    , PASS2_SPEED  = 1;

export default class Images2Video {
  /**
   * @param filePattern - file path plus name pattern
   *                      containing "%d", "%02d" etc
   * @param frameRate   - playback rate (default 30)
   */
  constructor(filePattern, frameRate = 30) {
    if (!/%0?\d?d/.test(filePattern)) {
      throw new Error(`invalid file name pattern`);
    }
    this.args = {
      input: filePattern
    , rate: +frameRate
    };
  }

  /**
   * encode image files into video
   *
   * @param  destFile - output .webm file
   * @return {Promise}
   */
  async encode(destFile = "video.webm") {
    if (!destFile.endsWith('.webm')) {
      throw new Error(`output file must be .webm`);
    }
    await this._pass1();
    await this._pass2(destFile);
  }

  async _pass1() {
    console.log(`FFmpeg pass 1:`, FFMPEG_LOG);

    let args = Object.assign({
          pass:   1
        , speed:  PASS1_SPEED
        , output: DEV_NULL
        }, this.args);

    let command = format(FFMPEG_PASS1, args)
      , result  = await exec(command);

    if (result.stderr ||
        !await fsAsync.exists(FFMPEG_LOG)) {
      throw new Error(`FFmpeg pass 1 failed:
${result.stderr}`);
    }
  }

  async _pass2(destFile) {
    console.log(`FFmpeg pass 2:`, destFile);

    let args = Object.assign({
          pass:   2
        , speed:  PASS2_SPEED
        , output: destFile
        }, this.args);

    let command = format(FFMPEG_PASS2, args)
      , result  = await exec(command);

    await fsAsync.remove(FFMPEG_LOG);

    if (result.stderr ||
        !await fsAsync.exists(destFile)) {
      throw new Error(`FFmpeg pass 2 failed:
${result.stderr}`);
    }
  }
}