rtl_fm stream with ffmpeg and low bandwith

Question

I currently try to stream audio from rtl_fm via ffmpeg to node-media-server.

This is working fine.

rtl_fm -f 103.0M -M fm -s 44.1k -A std -l 1 -g 40 |
ffmpeg -f s16le -ac 1 -i pipe:0 -f flv rtmp://192.168.178.42/live/lorem

But: The I want to listen to the signal from the frequency e.g. 83.0M and the bandwith (-s) is set to 20k.

Now the streamed audio is to fast. The audio sounds like pitched up and the terminal output of ffmpeg for speed is about 0.5x instead of 1x.

How can i stream this frequency with a bandwith of 20k without getting a bad output?

Are you receiving stereo output at the new freq? Change to -ac 2 and check. — Gyan, Feb 13 '19 at 11:42
No, this ist also mono, got the same issue on the 103.0M setting -s to 20k. — Felix Bäder, Feb 13 '19 at 12:07

score 2 · Accepted Answer · answered Feb 13 '19 at 12:30

As per the rtl_fm guide, -s is the output sampling rate, so you need to adjust that in the ffmpeg input parameter.

rtl_fm -f 83.0M -M fm -s 20k -A std -l 1 -g 40 |
ffmpeg -f s16le -channels 1 -sample_rate 20k -i pipe:0 -f flv rtmp://192.168.178.42/live/lorem

1 Answers1