Bug 1393687 reports a regression with the max-fr parameter, but as far as I can tell, we've never actually supported it. I don't see any code in the sdp parser to handle it. Fixing this will require adding support for parsing max-fr and plumbing it through to the VideoConduit code.

We find the code in mozilla-esr52 & mozilla-central: https://dxr.mozilla.org/mozilla-esr52/source/media/webrtc/signaling/src/sdp/sipcc/sdp_attr.c#1275 result1 = sdp_get_fmtp_tok_val(sdp_p, &fmtp_ptr, "max-fr", tmp, sizeof(tmp), &tok, &strtoul_result, 0, -1, UINT_MAX); https://dxr.mozilla.org/mozilla-esr52/source/media/webrtc/signaling/src/sdp/SipccSdpAttributeList.cpp#682 sdp_attr_t* attr = sdp_find_attr(sdp, level, 0, SDP_ATTR_FMTP, i); h264Parameters->max_mbps = fmtp->max_mbps; h264Parameters->max_fs = fmtp->max_fs; vp9Parameters->max_fs = fmtp->max_fs; vp9Parameters->max_fr = fmtp->max_fr; vp8Parameters->max_fs = fmtp->max_fs; vp8Parameters->max_fr = fmtp->max_fr; https://dxr.mozilla.org/mozilla-esr52/source/media/webrtc/signaling/src/jsep/JsepCodecDescription.h#495 mConstraints.maxFs = vp8Params.max_fs; mConstraints.maxFps = vp8Params.max_fr; We use the max-fs & max-mbps to control the framesize and framerate in H264 , use the max-fs & max-fr to control the framesize and framerate in VP8 before firefox 52 . It all works right before. but the framerate can not be controlled since firefox 53 (H264： we find that the max-mbps has been disabled in h264)

Yes, you're right, I looked at the same files yesterday and somehow missed this.