Fixes and improvements
- RTSP source: Persist credentials on source redirections (bluenviron/gortsplib#124)
- RTSP server: fix RTCP report in case of non-H264 tracks
- HLS muxer: fix error "wrong nal_ref_idc" (#966)
- HLS muxer, RTMP server: extract DTS from NALUs instead of estimating it
- HLS muxer: improve performance, decrease memory consumption
- HLS muxer: cache content of init.mp4
- HLS muxer: do not use EXT-X-GAP with fmp4 variant