ffmpeg error "Output file is empty, nothing was encoded" when trying to increase the tempo (speed up) mp3 file

Question

I'm trying to increase the tempo of an mp3 file using ffmpeg and atempo filter, but always get "Output file is empty, nothing was encoded"

this is the output log

ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 10.2.1 (GCC) 20200726
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libgsm --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
[mp3 @ 0000023bf37fdbc0] Estimating duration from bitrate, this may be inaccurate
Input #0, mp3, from 'normal.mp3':
  Metadata:
    encoder         : Lavf58.65.100
  Duration: 00:00:05.93, start: 0.000000, bitrate: 32 kb/s
    Stream #0:0: Audio: mp3, 22050 Hz, mono, fltp, 32 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (mp3 (mp3float) -> mp3 (mp3_mf))
Press [q] to stop, [?] for help
[mp3_mf @ 0000023bf3822880] MFT name: 'MP3 Encoder ACM Wrapper MFT'
Output #0, mp3, to 'faster.mp3':
  Metadata:
    TSSE            : Lavf58.45.100
    Stream #0:0: Audio: mp3 (mp3_mf), 22050 Hz, mono, s16, 128 kb/s
    Metadata:
      encoder         : Lavc58.91.100 mp3_mf
size=       0kB time=00:00:05.42 bitrate=   0.7kbits/s speed= 116x
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

this is the command I'm using ffmpeg -i normal.mp3 -af "atempo=1.1" faster.mp3

Answer 1

Use a specific audio encoder with -c:a

try

ffmpeg -i normal.mp3 -c:a libshine -af "atempo=1.1" faster.mp3

or

ffmpeg -i normal.mp3 -c:a libmp3lame -af "atempo=1.1" faster.mp3