Function extractPngMetadataFromBuffer

packages/engine/src/utils/ffprobe.ts:140–211

(buf: Buffer)

}

export function extractPngMetadataFromBuffer(buf: Buffer): StillImageMetadata | null {
  if (
    buf.length < 8 ||
    buf[0] !== 137 ||
    buf[1] !== 80 ||
    buf[2] !== 78 ||
    buf[3] !== 71 ||
    buf[4] !== 13 ||
    buf[5] !== 10 ||
    buf[6] !== 26 ||
    buf[7] !== 10
  ) {
    return null;
  }

  let width = 0;
  let height = 0;
  let seenIdat = false;
  let pos = 8;
  while (pos + 12 <= buf.length) {
    const chunkLen = buf.readUInt32BE(pos);
    const chunkType = buf.toString("ascii", pos + 4, pos + 8);
    if (pos + 12 + chunkLen > buf.length) return null;
    const chunkData = buf.subarray(pos + 8, pos + 8 + chunkLen);
    const chunkCrc = buf.readUInt32BE(pos + 8 + chunkLen);
    const chunkBytes = Buffer.concat([Buffer.from(chunkType, "ascii"), chunkData]);
    if (crc32(chunkBytes) !== chunkCrc) return null;

    if (chunkType === "IHDR" && chunkLen >= 8) {
      width = buf.readUInt32BE(pos + 8);
      height = buf.readUInt32BE(pos + 12);
    }

    if (chunkType === "IDAT") {
      seenIdat = true;
    }

    if (chunkType === "cICP" && chunkLen === 4 && !seenIdat) {
      const primariesCode = chunkData[0] ?? 0;
      const transferCode = chunkData[1] ?? 0;
      const matrixCode = chunkData[2] ?? 0;

      return {
        width,
        height,
        colorSpace: {
          colorPrimaries:
            primariesCode === 9
              ? "bt2020"
              : primariesCode === 1
                ? "bt709"
                : `unknown-${primariesCode}`,
          colorTransfer:
            transferCode === 16
              ? "smpte2084"
              : transferCode === 18
                ? "arib-std-b67"
                : transferCode === 1