[ID3 Dev] ATXT and CTOC/CHAP feedback

[Jud White]

Hello,

I have some feedback on ATXT and CTOC/CHAP.  I think it would be best to add some clarification before implementation is widespread.

CTOC/CHAP - Syncsafe frame sizes are explicitly shown in the examples.  I think a disambiguation between 2.3 and 2.4 frame sizes should be included to ensure implementations don't use syncsafe frame sizes in 2.3 tags.  As a side note I also agree with displaying this information more prominently in the 2.4 spec, maybe with a big red apple next to it to catch a certain company's attention.

ATXT - Some more data points for the scrambling would be helpful, maybe even an example of what the first few bytes of an attached WAV file would look like.  If there's a name for this technique maybe include it in the text so authors can find additional resources or implementations in their programming language.

Sample of pseudo-random sequence:

000: 11111110 (0xFE)
001: 00000100 (0x04)
002: 00011000 (0x18)
003: 01010001 (0x51)
...
126: 01110011 (0x73)
127: 00101010 (0x2A)

Example:

0x52 0x49 0x46 0x46 ('RIFF')

0x52 ^ 0xFE = 0xAC
0x49 ^ 0x04 = 0x4D
0x46 ^ 0x18 = 0x5E
0x46 ^ 0x51 = 0x17

Might want to check my math if you decide to update the article :)

Jud


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