mov.js

// ISOBMFF constants.
const BOX_HEADER_SIZE = 8;
const BOX_FTYP = 0x66747970;
const BOX_META = 0x6d657461;
const BOX_ILOC = 0x696c6f63;
const BOX_IPRP = 0x69707270;
const BOX_IPCO = 0x6970636f;
const BOX_ISPE = 0x69737065;

// MOV container stub with single video track.
const MOV_HEADER = (function() {
  const u32 = new Uint32Array([469762048,1887007846,1836020585,131072,1836020585,846164841,825520237,1140981760,1987014509,1811939328,1684567661,0,0,0,3892510720,704643072,256,1,0,0,256,0,0,0,256,0,0,0,64,0,0,0,0,0,0,33554432,3489726464,1801548404,1543503872,1684564852,50331648,0,0,16777216,0,704643072,0,0,0,0,256,0,0,0,256,0,0,0,64,32775,14340,1812004864,1634296941,536870912,1684563053,0,0,0,3227320320,3909287936,50261,553648128,1919706216,0,0,1701079414,0,0,0,16777216,1852402979,102,1752004116,100,1,0,0,1852400676,102,1701995548,102,0,1,1819440396,32,1,1651799011,108,1937011583,100,0,1,813064559,49,0,1,0,0,0,75499264,4718648,4718592,0,65536,0,0,0,0,0,0,0,0,16776984,1629028352,2168664438,167775240,11,3284118338,31915895,402653184,1937011827,0,16777216,16777216,3909287936,469762048,1668510835,0,16777216,16777216,16777216,16777216,335544320,2054386803,0,0,16777216,335544320,1868788851,0,16777216,1744961536,0,1952539757]);
  return new Uint8Array(u32.buffer);
})();
const MOV_HEADER_SIZE = MOV_HEADER.byteLength;
const MOV_STSZ_OFFSET = 568;
const MOV_MDAT_OFFSET = 608;
const MOV_TKHD_WIDTH_OFFSET = 234;
const MOV_AV01_WIDTH_OFFSET = 437;

function assert(cond, str) {
  if (!cond) throw new Error(str);
}

// Extract OBU.
export function avif2obu(ab) {
  function getU8() {const v = view.getUint8(pos); pos += 1; return v;}
  function getU16() {const v = view.getUint16(pos); pos += 2; return v;}
  function getU32() {const v = view.getUint32(pos); pos += 4; return v;}

  const view = new DataView(ab);
  const len = ab.byteLength;
  let pos = 0;

  let brandsCheck = false;
  let width = 0;
  let height = 0;
  let data =  null;

  while (pos < len) {
    const size = getU32();
    const type = getU32();
    const end = pos + size - BOX_HEADER_SIZE;
    assert(size >= BOX_HEADER_SIZE, "corrupted file");

    // TODO(Kagami): Add box version checks!
    switch (type) {
    case BOX_FTYP:
      // FIXME(Kagami): Check brands.
      // TODO(Kagami): Also check that meta/hdlr.handler = "pict".
      brandsCheck = true;
      break;
    case BOX_META:
      pos += 1; // version
      pos += 3; // flags
      continue;
    case BOX_IPRP:
      continue;
    case BOX_IPCO:
      continue;
    case BOX_ISPE:
      pos += 1; // version
      pos += 3; // flags
      width = getU32();
      height = getU32();
      break;
    case BOX_ILOC:
      pos += 1; // version
      pos += 3; // flags
      const offsetSizeAndLengthSize = getU8();
      const offsetSize = offsetSizeAndLengthSize >>> 4;
      assert(offsetSize < 8, "unsupported offset size");
      const lengthSize = offsetSizeAndLengthSize & 0xf;
      assert(lengthSize < 8, "unsupported length size");
      const baseOffsetSize = getU8() >>> 4;
      assert(baseOffsetSize < 8, "unsupported base offset size");
      const itemCount = getU16();
      assert(itemCount >= 1, "bad iloc items number");
      // XXX(Kagami): Choosing first item for simplicity.
      // TODO(Kagami): Use primary item (meta/pitm/item_ID).
      // TODO(Kagami): Also check that meta/iinf/infe[i].item_type = "av01".
      pos += 2; // item_ID
      pos += 2; // data_reference_index
      const baseOffset = baseOffsetSize === 4 ? getU32() : 0;
      pos += 2; // extent_count (>= 1)
      // XXX(Kagami): What should we do if extent_count > 1?
      const extentOffset = offsetSize === 4 ? getU32() : 0;
      const extentLength = lengthSize === 4 ? getU32() : 0;
      const u8 = new Uint8Array(ab);
      const offset = baseOffset + extentOffset;
      data = u8.subarray(offset, offset + extentLength);
      break;
    }

    pos = end;
  }

  assert(brandsCheck, "bad brands");
  assert(width && height, "bad image width or height");
  assert(data, "picture data not found");
  return {width, height, data};
}

// Embed OBU into MOV container stub as video frame.
// TODO(Kagami): Fix matrix, bitdepth, av1C metadata.
export function obu2mov({width, height, data}) {
  const fileSize = MOV_HEADER_SIZE + data.byteLength;
  const ab = new ArrayBuffer(fileSize);
  const view = new DataView(ab);
  const u8 = new Uint8Array(ab);
  u8.set(MOV_HEADER);
  u8.set(data, MOV_HEADER_SIZE);
  // |....|stsz|.|...|xxxx|
  view.setUint32(MOV_STSZ_OFFSET + BOX_HEADER_SIZE + 4, data.byteLength);
  // |xxxx|mdat|
  view.setUint32(MOV_MDAT_OFFSET, data.byteLength + BOX_HEADER_SIZE);
  // |xxxx|xxxx|
  view.setUint32(MOV_TKHD_WIDTH_OFFSET, width);
  view.setUint32(MOV_TKHD_WIDTH_OFFSET + 4, height);
  // |xx|xx|
  view.setUint16(MOV_AV01_WIDTH_OFFSET, width);
  view.setUint16(MOV_AV01_WIDTH_OFFSET + 2, height);
  return ab;
}

// Remux AVIF picture as MOV video with single frame.
export function avif2mov(ab) {
  return obu2mov(avif2obu(ab));
}