H265: parse sprop-vps/sps/pps from SDP for cameras that don't inline parameter sets

[kumaakh]

Problem

RFC 7798 §7.2 defines three H265-specific SDP fmtp attributes: sprop-vps, sprop-sps, sprop-pps. These carry the VPS/SPS/PPS parameter sets out-of-band in the SDP, exactly as H264 uses sprop-parametersets.

The live555-2013 MediaSubsession class only exposes fmtp_spropparametersets() (the H264 attribute). There are no accessors for the H265 equivalents, so Live555.cpp SetupSubsession passes NULL as the sprops for H265 streams.

Impact: cameras that do not inline VPS/SPS/PPS in every RTP stream (i.e., do not send them before the first IDR frame) will produce a black frame until the next keyframe. Cameras that inline them (like the Milesight MS-C5372 tested in #17) are unaffected.

Fix

1. Add fSpropVPS, fSpropSPS, fSpropPPS fields and accessors (fmtp_spropvps(), fmtp_spropsps(), fmtp_sproppps()) to libs/live555-2013.02.11/liveMedia/include/MediaSession.hh and populate them in the FMTP parser (MediaSession.cpp).
2. In Live555.cpp SetupSubsession, for H265 streams, concatenate sprop-vps, sprop-sps, sprop-pps and pass them as the sprops string to InitVideoSubsession.

Reference

• RFC 7798 §7.2: https://www.rfc-editor.org/rfc/rfc7798#section-7.2
• Tracked in Live555.cpp SetupSubsession with TODO(H265: parse sprop-vps/sps/pps from SDP for cameras that don't inline parameter sets #20) comment.