How to use FEC feature for Opus codec

Question

I'm trying to use the opus Forward Error Correction (FEC) feature. I have a service which does the encoding with OPUS_SET_INBAND_FEC(1) and OPUS_SET_PACKET_LOSS_PERC(20) with 10ms packets and sends them over UDP.

I'm not clear on the decoding process though.

1. When a packet is lost, do I need to call decode with fec=1 ONLY or do I need to call decode with fec=0 after as well on the next packet?
2. How do I know up front the size of the pcm that I send to decode with fec enabled?

Stearns

Answer 1

I managed to make it work.

The encoding part stated in the question was correct:

• Use the encoder OPUS_SET_INBAND_FEC(1) and OPUS_SET_PACKET_LOSS_PERC(X) where x>0 ans x<100
• Send packets with a duration of at least 10ms (for example: 480 samples at 48 kHz)

For the decoding part, when a packet is lost, call the decode function on the next packet first with fec=1 and again with fec=0.

When calling decode with fec=1, the pcm sent will be entirely filled. If you don't know the length that the pcm should be use on the decoder OPUS_GET_LAST_PACKET_DURATION(x) where x will get the the duration of the last packet.

Stearns

I'm trying to figure out how to to use inband fec. Could you please provide an example of the decoder part? – Politian

@Politian Maybe this helps? ddanilov.me/how-to-enable-in-band-fec-for-opus-codec – Ssm

@nh2, it is my post that I wrote after figured out how to configure FEC. So yeah, it might help! :) – Politian

@Politian Haha, nice! – Ssm