WAV文件ChunkSize计算逻辑疑问：请求解析各数值来源

Let's break down those confusing magic numbers (4, 8) in the formula by mapping them directly to the structure of a WAV file's RIFF chunk.

First, here's the core structure of a standard WAV file's top-level RIFF chunk:

RIFF Chunk Structure:
1. ChunkID: 4 bytes (fixed as "RIFF")
2. ChunkSize: 4 bytes (the field you're trying to understand)
3. Format: 4 bytes (fixed as "WAVE")
4. SubChunk1 (Format Chunk):
   - SubChunk1ID: 4 bytes (e.g., "fmt ")
   - SubChunk1Size: 4 bytes (size of the format data, usually 16 for PCM)
   - SubChunk1Data: [SubChunk1Size] bytes (audio format details like sample rate, bit depth)
5. SubChunk2 (Data Chunk):
   - SubChunk2ID: 4 bytes (e.g., "data")
   - SubChunk2Size: 4 bytes (size of the raw audio data)
   - SubChunk2Data: [SubChunk2Size] bytes (the actual sound samples)

Now let's unpack the formula from the documentation:
4 + (8 + SubChunk1Size) + (8 + SubChunk2Size)

• The first 4 corresponds to the Format field ("WAVE") which takes up exactly 4 bytes immediately after the ChunkSize field.
• Each 8 in the subchunk terms comes from combining two mandatory 4-byte fields in every WAV subchunk:
  • 4 bytes for the subchunk's unique ID (like "fmt " for the format chunk or "data" for the audio data chunk)
  • 4 bytes for the subchunk's size value (SubChunk1Size or SubChunk2Size)
    Adding those two gives 4 + 4 = 8. We then add SubChunk1Size/SubChunk2Size to account for the actual data stored in each subchunk.

The simplified 36 + SubChunk2Size version is just a shortcut for standard PCM WAV files, where SubChunk1Size is always 16. Plugging that value into the full formula:
4 + (8 + 16) + (8 + SubChunk2Size) = 4 + 24 + 8 + SubChunk2Size = 36 + SubChunk2Size

And to confirm with the other note from the docs: "This is the size of the entire file in bytes minus 8 bytes for the two fields not included in this count: ChunkID and ChunkSize" — this checks out because the total file size is calculated as:
ChunkID(4) + ChunkSize(4) + [the rest of the file (which equals ChunkSize)]
Rearranging that gives ChunkSize = Total File Size - 8 (subtracting the 4+4 bytes of ChunkID and ChunkSize themselves, which aren't included in the ChunkSize value).

内容的提问来源于stack exchange，提问作者Belphegor