ditto/packages/transcode/ffmpeg.ts

export interface FFmpegFlags {
  'c:v'?: string;
  'preset'?: string;
  'loglevel'?: string;
  'crf'?: string;
  'c:a'?: string;
  'b:a'?: string;
  'movflags'?: string;
  'f'?: string;
  [key: string]: string | undefined;
}

export function ffmpeg(input: URL | ReadableStream<Uint8Array>, flags: FFmpegFlags): ReadableStream<Uint8Array> {
  const args = ['-i', input instanceof URL ? input.href : 'pipe:0'];

  for (const [key, value] of Object.entries(flags)) {
    if (typeof value === 'string') {
      args.push(`-${key}`, value);
    }
  }

  args.push('pipe:1'); // Output to stdout

  // Spawn the FFmpeg process
  const command = new Deno.Command('ffmpeg', {
    args,
    stdin: input instanceof ReadableStream ? 'piped' : undefined,
    stdout: 'piped',
  });

  const child = command.spawn();

  // Pipe the input stream into FFmpeg stdin and ensure completion
  if (input instanceof ReadableStream) {
    input.pipeTo(child.stdin);
  }

  // Return the FFmpeg stdout stream
  return child.stdout;
}