I recently received the Blackmagic Design Decklink SDI card, and it does work with JB's addition of "HDMI" capture to Kdenlive. Should we rename that to "Blackmagic?" Here is how I converted the NTSC raw files it captured to lossless (huffyuv/flac) Matroska:
ffmpeg -f rawvideo -s 720x486 -r ntsc -pix_fmt uyvy422 -i capture_video_0000.raw -ar 48000 -ac 2 -f s16le -i capture_audio_0000.raw -flags +ilme+ildct -vcodec huffyuv -acodec flac -y test.mkv -- +-DRD-+
