[FFmpeg-user] Large Sized output files recieved while encoding the audio

Ferdi Scholten ferdi at sttc-nlp.nl
Wed Apr 20 17:37:59 EEST 2022


Hi,
> When I run ffmpeg command on a wav file, the received output file is of
> large size as compared to the original file. The command and the output are
> below,
>
> *FFMPEG command*
>
>   % ~/Downloads/audio/ffmpeg -i call-redacted.wav output.wav
>
> ffmpeg version 4.4.1-tessus  https://evermeet.cx/ffmpeg/  Copyright (c)
> 2000-2021 the FFmpeg developers
>
>    built with Apple clang version 11.0.0 (clang-1100.0.33.17)
>
>    configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg
> --extra-version=tessus --enable-avisynth --enable-fontconfig --enable-gpl
> --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d
> --enable-libfreetype --enable-libgsm --enable-libmodplug
> --enable-libmp3lame --enable-libmysofa --enable-libopencore-amrnb
> --enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg
> --enable-libopus --enable-librubberband --enable-libshine
> --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora
> --enable-libtwolame --enable-libvidstab --enable-libvmaf
> --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwebp
> --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid
> --enable-libzimg --enable-libzmq --enable-libzvbi --enable-version3
> --pkg-config-flags=--static --disable-ffplay
>
>    libavutil      56. 70.100 / 56. 70.100
>
>    libavcodec     58.134.100 / 58.134.100
>
>    libavformat    58. 76.100 / 58. 76.100
>
>    libavdevice    58. 13.100 / 58. 13.100
>
>    libavfilter     7.110.100 /  7.110.100
>
>    libswscale      5.  9.100 /  5.  9.100
>
>    libswresample   3.  9.100 /  3.  9.100
>
>    libpostproc    55.  9.100 / 55.  9.100
>
> Input #0, mp3, from 'call-redacted.wav':
>
>    Metadata:
>
>      encoder         : Lavf58.45.100
>
>    Duration: 00:13:06.38, start: 0.138125, bitrate: 64 kb/s
>
>    Stream #0:0: Audio: mp3, 8000 Hz, stereo, fltp, 64 kb/s
>
> Stream mapping:
>
>    Stream #0:0 -> #0:0 (mp3 (mp3float) -> pcm_s16le (native))
>
> Press [q] to stop, [?] for help
>
> Output #0, wav, to 'output.wav':
>
>    Metadata:
>
>      ISFT            : Lavf58.76.100
>
>    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 8000 Hz, stereo,
> s16, 256 kb/s
>
>      Metadata:
>
>        encoder         : Lavc58.134.100 pcm_s16le
>
> size=   24569kB time=00:13:06.17 bitrate= 256.0kbits/s speed=2.97e+03x
>
> video:0kB audio:24569kB subtitle:0kB other streams:0kB global headers:0kB
> muxing overhead: 0.000310
>
>
> *Input and output file sizes*
>
> du -sh call-redacted.wav
>
> 6.5M call-redacted.wav
>
> du -sh output.wav
>
>   24M output.wav
>
>
> Alternatively, when I run the same command but change the output
> file's extension to mp3, the correct sized file is returned. But the time
> taken (6 seconds) in this case is quite higher than the previous case(less
> than 1 second). The command and output is below,
>
>
>
> ~/Downloads/audio/ffmpeg -i call-redacted.wav output.mp3
>
> ffmpeg version 4.4.1-tessus  https://evermeet.cx/ffmpeg/  Copyright (c)
> 2000-2021 the FFmpeg developers
>
>    built with Apple clang version 11.0.0 (clang-1100.0.33.17)
>
>    configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg
> --extra-version=tessus --enable-avisynth --enable-fontconfig --enable-gpl
> --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d
> --enable-libfreetype --enable-libgsm --enable-libmodplug
> --enable-libmp3lame --enable-libmysofa --enable-libopencore-amrnb
> --enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg
> --enable-libopus --enable-librubberband --enable-libshine
> --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora
> --enable-libtwolame --enable-libvidstab --enable-libvmaf
> --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwebp
> --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid
> --enable-libzimg --enable-libzmq --enable-libzvbi --enable-version3
> --pkg-config-flags=--static --disable-ffplay
>
>    libavutil      56. 70.100 / 56. 70.100
>
>    libavcodec     58.134.100 / 58.134.100
>
>    libavformat    58. 76.100 / 58. 76.100
>
>    libavdevice    58. 13.100 / 58. 13.100
>
>    libavfilter     7.110.100 /  7.110.100
>
>    libswscale      5.  9.100 /  5.  9.100
>
>    libswresample   3.  9.100 /  3.  9.100
>
>    libpostproc    55.  9.100 / 55.  9.100
>
> Input #0, mp3, from 'call-redacted.wav':
>
>    Metadata:
>
>      encoder         : Lavf58.45.100
>
>    Duration: 00:13:06.38, start: 0.138125, bitrate: 64 kb/s
>
>    Stream #0:0: Audio: mp3, 8000 Hz, stereo, fltp, 64 kb/s
>
> Stream mapping:
>
>    Stream #0:0 -> #0:0 (mp3 (mp3float) -> mp3 (libmp3lame))
>
> Press [q] to stop, [?] for help
>
> Output #0, mp3, to 'output.mp3':
>
>    Metadata:
>
>      TSSE            : Lavf58.76.100
>
>    Stream #0:0: Audio: mp3, 8000 Hz, stereo, fltp
>
>      Metadata:
>
>        encoder         : Lavc58.134.100 libmp3lame
>
> size=    2304kB time=00:13:06.17 bitrate=  24.0kbits/s speed= 130x
>
> video:0kB audio:2304kB subtitle:0kB other streams:0kB global headers:0kB
> muxing overhead: 0.011063
>
> du -sh output.mp3
>
> 3.3M output.mp3
>
>
> Please help me out in identifying the right command options for optimum
> time and filesize.
>
>
> Regards,
>
> Shubham
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The fact that the file extension is .wav does not mean it also is an 
uncompressed pcm wav file. In this case as correctly identified by 
ffmpeg it is an mp3 file (lossy compressed audio) that will always get 
bigger when converted to uncompressed pcm. Which is what your first 
command does. It decodes the mp3 and stores the uncompressed stream in 
pcm format.

Your second command actually encodes the already encoded file again, 
reducing the quality of the audio even further as 64 kb is already very 
low quality for an mp3 file. This is also why it takes longer.

So what are you trying to achieve?

Greetings Ferdi



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