0

ISO/IEC 23001-7 Common encryption in ISO base media file defines a subsample as:

9.5 Subsample encryption

9.5.1 Definition (Normative)

Subsample encryption SHALL divide each sample into one or more contiguous Subsamples. Each Subsample SHALL have an unprotected part followed by a protected part, only one of which MAY be zero bytes in length. (Note: usually both are non-zero values). The total length of all of the Subsamples (BytesOfClearData + BytesOfProtectedData for all Subsamples that make up a sample) SHALL be equal to the size of the sample itself, and they SHALL not overlap.

The specification provides some examples with 8 subsamples per sample.

I can't find any mention of an upper limit for the allowed subsample count.

In a production environment, I encountered streams with up to 10 subsamples per sample.

Is there a limit to the subsample count in specification? It could be in a different document.

Martin
  • 3,960
  • 7
  • 43
  • 43

1 Answers1

0

subsample_count is encoded as an unsigned 16 bit integer. Hence the maximum number is 65535.

szatmary
  • 29,969
  • 8
  • 44
  • 57
  • I'm looking for a non purely technical limit, if it exists. For example, `IV_size` is defined as an unsigned 8 bit integer but can only have 0, 8 and 16 as valid values. – Martin Sep 25 '18 at 06:14