FFmpeg map optional (audio) stream

Question

I use this command to produce a file scaled and with an overlay image:

ffmpeg 
-i input.* -i overlay.png 
-filter_complex "[0:v]...; ...[1:v]overlay=... ... [resultingvideo]" 
-map "[resultingvideo]" -vcodec libx264 -f mp4 
-acodec libmp3lame -q:a 50 
outputfilename.mov

where "..." represents some left out filtering.

The problem is, there is no audio.

If I add -map 0:a, there is audio if the input has audio, and an error and no output file if the input has no audio.

How can I get ffmpeg to optionally use the audio from the input if it exists, and otherwise ignore audio or produce silence or something?

Or, do I have to analyze the file first using ffprobe before I can generate my script command?

Solution

Recent versions of ffmpeg support a conditional mapping option:

ffmpeg -i input.mp4 -map "0:a?" output.mp4

This will ignore non-existing audio streams in the input file.

Comments

[rupinderjeet]

[0:a?] how can I do something like this in filter_complex