Handle malformed SDP from Hikvision cameras

[thomaspurchas]

Adds function to detect and remove malformed fmtp lines emitted by some camera when streaming H265. Malformed fmtp line can cause issues downstream, notably if FFmpeg is used to de-mux and remux the H265 stream without transcoding. Removal of malformed fmtp forces downstream process to extract the VPS, SPS and PPS value from bitstream NALs.

Example of an SDP with malformed fmtp:

v=0
o=- 1739057148693902 1739057148693902 IN IP4 192.168.254.19
s=Media Presentation
e=NONE
b=AS:5050
t=0 0
a=control:rtsp://192.168.254.19:554/streaming/channels/101/
m=video 0 RTP/AVP 96
c=IN IP4 0.0.0.0
b=AS:5000
a=recvonly
a=x-dimensions:1920,1080
a=control:rtsp://192.168.254.19:554/streaming/channels/101/trackID=1
a=rtpmap:96 H265/90000
a=fmtp:96 sprop-sps=QgECAWAAAAMAgAAAAwAAAwB4AACgA8CAEOf42td2pu7muVVgLcBAQEEAAAMD6AAAH0ByHe5RAHpgAIm8APTAARN4QB6YACJvAD0wAETeIA==; sprop-pps=RAHBcrCcFApiQAAA
a=Media_header:MEDIAINFO=494D4B48010200000400050000000000000000000000000000000000000000000000000000000000;
a=appversion:1.0

Here there fmtp has a sprop-sps, sprop-pps but is missing sprop-vps. When attempting to decode with FFmpeg this non-fatal error will be emitted by the demuxer:

[hevc @ 0x154e06810] VPS 0 does not exist

And this fatal error will be emitted by the muxer when trying to restream using RTSP

[out#0/rtsp @ 0x600001e5c000] Could not write header (incorrect codec parameters ?): Invalid data found when processing input

Malformed fmtp lines is likely the cause of these issues: #1545, blakeblackshear/frigate#5585

[AlexxIT]

Thanks!

[AlexxIT]

https://github.com/AlexxIT/go2rtc/releases/tag/v1.9.9