Encrypted and restricted SampleEntry classes

[podborski]

Currently the 8th edition lists Protected sample entry codes in Table 7 and Restricted sample entry codes in Table 8.

For text SimpleTextSampleEntry is mentioned as the sample entry class in both enct and rest.

For subtitles XMLSubtitleSampleEntry is mentioned encu and resu.

As I mentioned in this discussion MPEGGroup/FileFormatConformance#64 (comment) should this be more generic?

E.g. XMLSubtitleSampleEntry -> SubtitleSampleEntry and SimpleTextSampleEntry -> PlainTextSampleEntry?

[cconcolato]

We note that the tables have been renumbered (Table 13 and Table 14).
Today's design is such that when you encounter an encrypted sample entry, from the 4CC you should know how many bytes you have to skip to start parsing "boxes" and find the OriginalFormatBox. An alternative may need sniffing the other boxes.
We note that the encryption of metadata tracks points to the base sample entry type.
We welcome contributions to address this issue, e.g. notes telling players how to behave or use the reserved in the base SampleEntry class to point to the OriginalFormatBox.