The SCTE35 "section_length" value is always 3 bytes less than the actual size
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I'm learning SCTE35 staff and I can't figure out one thing. Why is the length of "section_length" always less than 3 bytes from the actual size?
Example:
>>> test_raw = "/DAlAAAAAAAAAP/wFAUAAAZ5f+/+AAAAAH4Ae5igAAAAAAAA5nk27g=="
>>> test_cue = Cue(test_raw)
>>> test_cue.decode()
>>> test_cue.show()
"section_length": 37,
But if I will check len(test_cue.bites) will see 40:
>>> len(test_cue.bites)
40
I've already checked the documentation but did not find answer:
- https://wagtail-prod-storage.s3.amazonaws.com/documents/SCTE_281-1_2023.pdf
- https://wagtail-prod-storage.s3.amazonaws.com/documents/SCTE_281-2_2023.pdf
- https://alexzambelli.com/blog/wp-content/uploads/SCTE-35%20In-Band%20Event%20Signaling%20%28Seattle%20Video%20Tech%20-%20Dec%202018%29.pdf
Probably some "header" that is not included in the "section_length". From the source of the lib i see that "section_length" calculation like this - # 11 bytes for info section + command + 2 descriptor loop length + descriptor loop + 4 for crc, but I`m still confused.
Сould someone please explain why we have this 3 byte difference in "section_length" and the actual size ?
Sorry, the question not related to the project
No problem man , that threw me for a while too.
(8 + 1 + 1 + 2 + 12 ) >> 3 = 3 bytes
Section Length is the number of bytes immediately following Section Length.
Does that make sense?