Adding a sine generated audio track to a video stream with ffmepg

Question

I'm generating an MPEG transport stream from a PNG file with ffmpeg succesfully with the following command:

ffmpeg -re -loop 1 -i smpte-color-bars-1080p.png -r 25 -vcodec libx264 -tune zerolatency -f mpegts udp://0.0.0.0:1234

I'd like to add an audio track to this usingthe sine function but am falling at the first hurdle.

I've tried:

ffmpeg -re -loop 1 -i smpte-color-bars-1080p.png -r 25 -vcodec libx264 -tune zerolatency -i sine=frequency=1000 -f mpegts udp://0.0.0.0:1234

and get the error:

Unknown decoder 'libx264'

Which implies that my arguments order is wrong.

So I then tried:

ffmpeg -re -loop 1 -i sine=frequency=1000 -i smpte-color-bars-1080p.png -r 25 -vcodec libx264 -tune zerolatency -f mpegts udp://0.0.0.0:1234

and get the error:

sine=frequency=1000: No such file or directory

What is the correct syntax for adding a sine generated audio in this case?

Answer 1

sine is a source filter, so the input format needs to be set as a filter using -f lavfi.

Use

ffmpeg -re -loop 1 -i smpte-color-bars-1080p.png -re -f lavfi -i sine=frequency=1000 -r 25 -vcodec libx264 -tune zerolatency -acodec aac -f mpegts udp://0.0.0.0:1234