RTMP: Support parse and convert HDR information.

[winlinvip]

In the new RTMP specification, the PacketType=PacketTypeMetadata is HDR, SRS need to parse it and convert to other formats. For example, MPEGTS or MP4 has its own specification.

Note that it should work good for RTMP clients, SRS will pass by it, because it's defined in video tags.

// VideoTagBody does not contain video data. VideoTagBody
 // instead contains an AMF encoded metadata. See Metadata Frame
 // section for an illustration of its usage. As an example, the metadata
 // can be HDR information. This is a good way to signal HDR
 // information. This also opens up future ways to express additional
 // metadata that is meant for the next video sequence.
 //
 // note: presence of PacketTypeMetadata means that FrameType
 // flags at the top of this table should be ignored
 4 = PacketTypeMetadata

See https://github.com/veovera/enhanced-rtmp/blob/main/enhanced-rtmp-v1.pdf

[winlinvip]

Please, @xiaozhihong, pay more attention to the HDR support plan. Not only RTMP, all protocols should support HDR.

TRANS_BY_GPT4