我在将 M4A 原子插入文件时遇到问题。由于原始文件没有 udta 结构，因此我使用现有的 M4A 文件添加它作为指南。
这是我添加原子的操作：
- 在内存中构建一个 udta atom
- 更新 moov atom 的大小以包含 udta atom 的大小
- 将文件复制到第一个 trak atom 的末尾
- 插入我的 udta atom
- 照常复制其余部分。
原始文件和标记文件之间唯一真正的区别是 mdat 原子被向下移动了一点以容纳标记。这让我相信在其他原子中有一些关于那个位置的参考，但我找不到。
这是 AtomicParsley 的输出：
原始文件：
Atom ftyp @ 0 of size: 36, ends @ 36
Atom moov @ 36 of size: 30156, ends @ 30192
Atom mvhd @ 44 of size: 108, ends @ 152
Atom iods @ 152 of size: 33, ends @ 185
Atom trak @ 185 of size: 30007, ends @ 30192
Atom tkhd @ 193 of size: 92, ends @ 285
Atom mdia @ 285 of size: 29907, ends @ 30192
Atom mdhd @ 293 of size: 32, ends @ 325
Atom hdlr @ 325 of size: 37, ends @ 362
Atom minf @ 362 of size: 29830, ends @ 30192
Atom smhd @ 370 of size: 16, ends @ 386
Atom dinf @ 386 of size: 36, ends @ 422
Atom dref @ 394 of size: 28, ends @ 422
Atom stbl @ 422 of size: 29770, ends @ 30192
Atom stts @ 430 of size: 24, ends @ 454
Atom stsd @ 454 of size: 106, ends @ 560
Atom mp4a @ 470 of size: 90, ends @ 560
Atom esds @ 506 of size: 54, ends @ 560
Atom stsz @ 560 of size: 26888, ends @ 27448
Atom stsc @ 27448 of size: 40, ends @ 27488
Atom stco @ 27488 of size: 2704, ends @ 30192
Atom mdat @ 30192 of size: 2495503, ends @ 2525695
修改文件：
Atom ftyp @ 0 of size: 36, ends @ 36
Atom moov @ 36 of size: 30323, ends @ 30359
Atom mvhd @ 44 of size: 108, ends @ 152
Atom iods @ 152 of size: 33, ends @ 185
Atom trak @ 185 of size: 30007, ends @ 30192
Atom tkhd @ 193 of size: 92, ends @ 285
Atom mdia @ 285 of size: 29907, ends @ 30192
Atom mdhd @ 293 of size: 32, ends @ 325
Atom hdlr @ 325 of size: 37, ends @ 362
Atom minf @ 362 of size: 29830, ends @ 30192
Atom smhd @ 370 of size: 16, ends @ 386
Atom dinf @ 386 of size: 36, ends @ 422
Atom dref @ 394 of size: 28, ends @ 422
Atom stbl @ 422 of size: 29770, ends @ 30192
Atom stts @ 430 of size: 24, ends @ 454
Atom stsd @ 454 of size: 106, ends @ 560
Atom mp4a @ 470 of size: 90, ends @ 560
Atom esds @ 506 of size: 54, ends @ 560
Atom stsz @ 560 of size: 26888, ends @ 27448
Atom stsc @ 27448 of size: 40, ends @ 27488
Atom stco @ 27488 of size: 2704, ends @ 30192
Atom udta @ 30192 of size: 167, ends @ 30359
Atom meta @ 30200 of size: 159, ends @ 30359
Atom ilst @ 30212 of size: 147, ends @ 30359
Atom ©ART @ 30220 of size: 35, ends @ 30255
Atom data @ 30228 of size: 27, ends @ 30255
Atom ©nam @ 30255 of size: 63, ends @ 30318
Atom data @ 30263 of size: 55, ends @ 30318
Atom ©alb @ 30318 of size: 41, ends @ 30359
Atom data @ 30326 of size: 33, ends @ 30359
Atom mdat @ 30359 of size: 2495503, ends @ 2525862
另一件值得注意的事是，我用作参考的标记文件在 udta->meta 下有一个 hdlr 原子，但添加该标记的副本也无济于事。如果我手动删除 udta atom 和 moov 的大小数据，该文件将再次运行。
当我尝试播放标记文件时，我在各种程序中收到这些错误：
mplayer:
[aac @ 0x204d720] channel element 0.0 is not allocated
[aac @ 0x204d720] channel element 0.0 is not allocated
[aac @ 0x204d720] channel element 3.13 is not allocated
[aac @ 0x204d720] channel element 2.14 is not allocated
[aac @ 0x204d720] channel element 2.9 is not allocated
[aac @ 0x204d720] Prediction is not allowed in AAC-LC.
[aac @ 0x204d720] channel element 3.1 is not allocated
[aac @ 0x204d720] channel element 0.3 is not allocated
....
totem:
** Message: Error: Could not decode stream.
gstfaad.c(1319): gst_faad_chain (): /GstPlayBin2:play/GstURIDecodeBin:uridecodebin0/GstDecodeBin2:decodebin20/GstFaad:faad0:
decoding error: Bitstream value not allowed by specification
banshee:
[Error 08:26:27.610] GStreamer stream error: Decode
[Error 08:26:27.960] GStreamer stream error: Decode
[Error 08:26:28.252] GStreamer resource error: NotFound
哦，我多么希望其他 99% 的程序能够识别除 MP3 以外的文件上的 ID3 标记....