ffmpeg Reduce the speed of an amr audio file by 50%

[kamalakar108]

Dear all,
When I reduce the speed of an mp3 file using ffmpeg it is excellently working. but when i try to reduce the speed of amr file it is not working.

ffmpeg -i a1.mp3 -filter:a "atempo=0.6" b1.mp3
the command works very well with mp3 files.

but is not working with amr files.

ffmpeg -i a1.amr -filter:a "atempo=0.6" b1.amr

Duration: 00:00:32.34, bitrate: 6 kb/s
Stream #0:0: Audio: amr_nb (samr / 0x726D6173), 8000 Hz, mono, flt
Automatic encoder selection failed for output stream #0:0. Default encoder for f
ormat amr (codec amr_nb) is probably disabled. Please choose an encoder manually
.

Error selecting an encoder for stream 0:0

amr file it is not accepting so i zipped it and uploaded it

Kindly help me in giving the right code.
Regards
Kamalakar

[Selur]

Sounds like ffmpeg normally would use amr_nb, but since it's not present in your ffmpeg build, ffmpeg requests that you set another encoder.
You will need an ffmpeg version which supports amr encoding, see: https://ffmpeg.org/general.html#OpenCORE-AMR

ffmpeg -encoders

lists the encoders supported by a ffmpeg version.

[kamalakar108]

Selur Sir, updated ffmpeg and it is working fine. Thanks a lot for your Reply.