For anyone that's still following this, I've found some FFMPEG settings that work:
vcodec = libx264 acodec = libfdk_aac pix_fmt = yuv420p threads = 2 scale_factor = 1 format = flv video_preset = ultrafast video_profile = main video_tune = animation video_bufsize = 512k video_minrate = 512k video_maxrate = 512k video_r = 60 video_g = 120 video_keyint_min = 60 sample_rate = 44100 audio_preset = aac_he_v2 audio_global_quality = 1You can read more about it in my post: How To Live Stream To Twitch from a RetroPie