remotion_service/server/services/render_video.ts

import type { DocumentInterface } from "@/srv/types/DocumentSchema";
import type { CaptionStyleConfigType } from "@/srv/types/CaptionStyleSchema";
import { serverConfig } from "@/srv/config";
import { statSync } from "node:fs";

const OUTPUT_DIR = "out";
const KILOBYTE = 1024;
const MEGABYTE = 1024 * KILOBYTE;
const MAX_CAPTURED_STREAM_OUTPUT_CHARS = 20_000;
const RENDER_CANCELLATION_POLL_MS = 1_000;

export const RENDER_CANCELLED_ERROR_MESSAGE = "Render cancelled";

export type RenderResult = {
  output: string;
};

export type RenderProgress = {
  renderedFrames: number;
  totalFrames: number;
};

function formatBytes(bytes: number): string {
  if (bytes >= MEGABYTE) {
    return `${(bytes / MEGABYTE).toFixed(1)} MB`;
  }

  if (bytes >= KILOBYTE) {
    return `${(bytes / KILOBYTE).toFixed(1)} KB`;
  }

  return `${bytes} B`;
}

function formatDuration(durationMs: number): string {
  return `${(durationMs / 1000).toFixed(1)}s`;
}

function appendCapturedOutput(current: string, nextLine: string): string {
  const combined = current
    ? `${current}\n${nextLine}`
    : nextLine;

  if (combined.length <= MAX_CAPTURED_STREAM_OUTPUT_CHARS) {
    return combined;
  }

  return combined.slice(-MAX_CAPTURED_STREAM_OUTPUT_CHARS);
}

function parseRenderProgressFromLine(
  line: string,
  onProgress?: (progress: RenderProgress) => void,
): void {
  if (!onProgress) {
    return;
  }

  const frameMatch = line.match(
    /(?:Rendered?\s+frame|Rendered|Encoded)\s+(\d+)\s*\/\s*(\d+)/i,
  );

  if (!frameMatch) {
    return;
  }

  onProgress({
    renderedFrames: parseInt(frameMatch[1], 10),
    totalFrames: parseInt(frameMatch[2], 10),
  });
}

async function consumeProcessStream(
  stream: ReadableStream<Uint8Array> | null | undefined,
  label: "stdout" | "stderr",
  onLine?: (line: string) => void,
): Promise<string> {
  if (!stream) {
    return "";
  }

  const reader = stream.getReader();
  const decoder = new TextDecoder();
  let buffer = "";
  let captured = "";

  try {
    while (true) {
      const { done, value } = await reader.read();
      if (done) {
        break;
      }

      buffer += decoder.decode(value, { stream: true });
      const lines = buffer.split("\n");
      buffer = lines.pop() || "";

      for (const line of lines) {
        const normalizedLine = line.trimEnd();
        if (!normalizedLine) {
          continue;
        }

        captured = appendCapturedOutput(captured, normalizedLine);
        console.log(`[render:${label}] ${normalizedLine}`);
        onLine?.(normalizedLine);
      }
    }

    const tail = buffer.trim();
    if (tail) {
      captured = appendCapturedOutput(captured, tail);
      console.log(`[render:${label}] ${tail}`);
      onLine?.(tail);
    }
  } catch (error) {
    console.warn(
      `[render:${label}] Stream reader closed unexpectedly: ${error instanceof Error ? error.message : String(error)}`,
    );
  }

  return captured;
}

export async function renderCaptionedVideo(
  transcription: DocumentInterface,
  videoSrc: string,
  filename: string,
  styleConfig?: CaptionStyleConfigType,
  onProgress?: (progress: RenderProgress) => void,
  shouldCancel?: () => boolean | Promise<boolean>,
): Promise<RenderResult> {
  const uniqueFilename = `${crypto.randomUUID()}-${filename}`;
  const outputPath = `${OUTPUT_DIR}/${uniqueFilename}`;
  const propsPath = `${OUTPUT_DIR}/${crypto.randomUUID()}.json`;

  const props: Record<string, unknown> = {
    videoSrc,
    transcription,
    fps: 30,
  };
  if (styleConfig) {
    props.styleConfig = styleConfig;
  }

  await Bun.write(propsPath, JSON.stringify(props));

  try {
    const renderStartedAt = Date.now();
    const args = [
      "render",
      "src/index.ts",
      serverConfig.REMOTION_COMPOSITION_ID,
      outputPath,
      "--props",
      propsPath,
    ];

    const cmd = ["./node_modules/.bin/remotion", ...args];
    console.log(`[render] Starting: ${cmd.join(" ")}`);
    console.log(`[render] Source video: ${videoSrc}`);
    console.log(`[render] Output: ${outputPath}, Props: ${propsPath}`);

    const proc = Bun.spawn(cmd, {
      stdout: "pipe",
      stderr: "pipe",
    });
    let renderCancelled = false;

    const stopRenderIfCancelled = async () => {
      if (!shouldCancel || renderCancelled) {
        return;
      }

      const cancellationRequested = await shouldCancel();
      if (!cancellationRequested) {
        return;
      }

      renderCancelled = true;
      proc.kill();
    };

    const cancellationTimer = shouldCancel
      ? setInterval(() => {
          void stopRenderIfCancelled();
        }, RENDER_CANCELLATION_POLL_MS)
      : null;

    const handleProcessLine = (line: string) => {
      parseRenderProgressFromLine(line, onProgress);
    };

    const stdoutPromise = consumeProcessStream(
      proc.stdout,
      "stdout",
      handleProcessLine,
    );
    const stderrPromise = consumeProcessStream(
      proc.stderr,
      "stderr",
      handleProcessLine,
    );

    const exitCode = await proc.exited;
    if (cancellationTimer) {
      clearInterval(cancellationTimer);
    }

    const [capturedStdout, capturedStderr] = await Promise.all([
      stdoutPromise,
      stderrPromise,
    ]);

    if (renderCancelled) {
      throw new Error(RENDER_CANCELLED_ERROR_MESSAGE);
    }

    if (exitCode !== 0) {
      console.error(
        `[render] Failed after ${formatDuration(Date.now() - renderStartedAt)} (exit ${exitCode})`,
      );
      if (capturedStdout) {
        console.error(`[render] Last stdout:\n${capturedStdout}`);
      }
      if (capturedStderr) {
        console.error(`[render] Last stderr:\n${capturedStderr}`);
      }
      throw new Error(
        `Render process exited with code ${exitCode}: ${(capturedStderr || capturedStdout).slice(0, 2000)}`,
      );
    }

    const outputSize = statSync(outputPath).size;
    console.log(
      `[render] Completed in ${formatDuration(Date.now() - renderStartedAt)} (${formatBytes(outputSize)})`,
    );

    return { output: outputPath };
  } finally {
    await Bun.file(propsPath).delete().catch(() => {});
  }
}