transcode_audio example report [NULL @ 000001eb0fb725c0] Unable to find a suitable output format for '111.mp3'

[skydig]

Please include as much info as possible to save me (solo maintainer helping for free) some time. A minimal, complete, and reproducible example is a must. Link to a gist if you don't feel like posting all the code inline. At the same time, please leave out unnecessary code so I don't need to wade through a hundred lines to get to the problematic part. Tell me your OS, FFmpeg version, etc. if there's even a slim chance of relevancy.
for ffmpeg5.0 under windows env