src/lib/utils/video.ts

/**
 * Extract the final frame from a video element as a Blob
 * This is used to create continuity between video segments
 * Similar to the approach in sora-extend, but using browser Canvas API
 */
export async function extractFinalFrame(
  videoElement: HTMLVideoElement
): Promise<Blob> {
  return new Promise((resolve, reject) => {
    try {
      // Create a canvas with the video's dimensions
      const canvas = document.createElement('canvas');
      canvas.width = videoElement.videoWidth;
      canvas.height = videoElement.videoHeight;

      const ctx = canvas.getContext('2d');
      if (!ctx) {
        reject(new Error('Could not get canvas context'));
        return;
      }

      // Draw the current frame onto the canvas
      ctx.drawImage(videoElement, 0, 0, canvas.width, canvas.height);

      // Convert canvas to blob
      canvas.toBlob(
        (blob) => {
          if (blob) {
            resolve(blob);
          } else {
            reject(new Error('Failed to create blob from canvas'));
          }
        },
        'image/jpeg',
        0.95 // High quality for better continuity
      );
    } catch (error) {
      reject(error);
    }
  });
}

/**
 * Seek to the last frame of a video and extract it
 * Useful for extracting the final frame before the video ends naturally
 */
export async function seekAndExtractFinalFrame(
  videoElement: HTMLVideoElement
): Promise<Blob> {
  return new Promise((resolve, reject) => {
    const handleSeeked = async () => {
      try {
        const blob = await extractFinalFrame(videoElement);
        videoElement.removeEventListener('seeked', handleSeeked);
        resolve(blob);
      } catch (error) {
        videoElement.removeEventListener('seeked', handleSeeked);
        reject(error);
      }
    };

    videoElement.addEventListener('seeked', handleSeeked);

    // Seek to 50ms before the end to ensure we get a valid frame
    const targetTime = Math.max(0, videoElement.duration - 0.05);
    videoElement.currentTime = targetTime;
  });
}

/**
 * Create a preview URL for a blob (useful for debugging)
 */
export function createBlobPreviewUrl(blob: Blob): string {
  return URL.createObjectURL(blob);
}

/**
 * Revoke a blob URL to free memory
 */
export function revokeBlobUrl(url: string): void {
  URL.revokeObjectURL(url);
}

/**
 * Download a blob as a file (useful for debugging/testing)
 */
export function downloadBlob(blob: Blob, filename: string): void {
  const url = createBlobPreviewUrl(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = filename;
  document.body.appendChild(a);
  a.click();
  document.body.removeChild(a);
  revokeBlobUrl(url);
}