When outputting HLS, support AnnexB format in RTMP packets.

[winlinvip]

https://github.com/winlinvip/simple-rtmp-server/issues/184

TRANS_BY_GPT3

[winlinvip]

In theory, RTMP should be in IBMF format, but sometimes it may also have annexb. SRS will detect the content format.

TRANS_BY_GPT3

[b04505009]

Hi, I would like to ask that where can I find the info of "RTMP should be in IBMF format", and is there an easy way to check that if my rtmp stream is IBMF or AnnexB? Thanks!