detect and raise version if specified too low

[thenewguy]

If the version is specified in a playlist that is too low, it should be raised when converted back to a string.

The following features aren't backward compatible. Older clients may fail to play the content if you use these features but don't specify the protocol version where they were introduced:

You must use at least protocol version 2 if you have IV in EXT-X-KEY.

You must use at least protocol version 3 if you have floating point EXTINF duration values.

You must use at least protocol version 4 if you have EXT-X-BYTERANGE or EXT-X-IFRAME-ONLY.

You must use at least protocol version 5 if you specify the SAMPLE-AES encryption method in EXT-X-KEY, or if you have KEYFORMAT and KEYFORMATVERSIONS attributes in EXT-X-KEY, or if you have EXT-X-MAP.

You must use at least protocol version 6 if you have EXT-X-MAP in a Media Playlist that does not contain EXT-X-I-FRAMES-ONLY.

You must use at least protocol version 7 if you specify "SERVICE" values for the INSTREAM-ID attribute of EXT-X-MEDIA.

You must use at least protocol version 8 if you use variable substitution.

Ref:

• https://developer.apple.com/documentation/http_live_streaming/about_the_ext-x-version_tag

[thenewguy]

I see there is an expected failure for this - is that because it will not be fixed or that it is waiting implementation?

[leandromoreira]

I don't know @thenewguy it seems very reasonable that m3u8 would check the version matching featuress... but I'm afraid it can broken current usages?!... maybe we could do that but let it off and only turn on when strict is True, what do you think?

cc @mauricioabreu @flavioribeiro @igorsobreira

PS: also maybe this VersionMatching thing should be placed into a self component (like a class...) instead of within the currrent parser, it can be used by the parser but not developed there.

[mauricioabreu]

I think it is ok to make it work when strict is on.