Hello, I try to make a low latency sound link with ffmpeg. With MP3, it works: Encoder: ffmpeg -re -f alsa -i default:CARD=CODEC -acodec mp3 -ab 128k -ac 2 -f rtp rtp://10.1.0.19:8000 Decoder: ffplay rtp://127.0.0.1:8000 It works! With libopus (better codec) Encoder: ffmpeg -re -f alsa -i default:CARD=CODEC -acodec libopus -ab 64k -ac 2 -f rtp rtp://10.1.0.19:8000 Decoder: ffplay rtp://127.0.0.1:8000 i have the error: [rtp @ 0xb45004a0] Unable to receive RTP payload type 97 without an SDP file describing it Input #0, rtp, from 'rtp://127.0.0.1:8000': Duration: N/A, bitrate: N/A Failed to open file 'rtp://127.0.0.1:8000' or configure filtergraph ffplay version N-81350-g3282e31 Copyright (c) 2003-2016 the FFmpeg developers built with gcc 4.9.2 (Raspbian 4.9.2-10) configuration: --arch=armel --target-os=linux --enable-ffplay --enable-gpl --enable-libvorbis --enable-libopus --enable-libfdk-aac --enable-libtwolame --enable-libmp3lame --enable-nonfree --extra-cflags=-I/arm/include --extra-ldflags=-L/arm/lib --extra-libs=-ldl Thanks,