How do you convert an entire directory with ffmpeg? [closed]

For Linux and macOS this can be done in one line, using parameter expansion to change the filename extension of the output file:

for i in *.avi; do ffmpeg -i "$i" "${i%.*}.mp4"; done

And on Windows:

FOR /F "tokens=*" %G IN ('dir /b *.flac') DO ffmpeg -i "%G" -acodec mp3 "%~nG.mp3"

For Windows:

Here I'm Converting all the (.mp4) files to (.mp3) files.
Just open cmd, goto the desired folder and type the command.

Shortcut: (optional)

1. Goto the folder where your (.mp4) files are present
   
2. Press Shift and Right click and Choose "Open PowerShell Window Here"
   or "Open Command Prompt Window Here"
   
3. Type "cmd" [NOTE: Skip this step if it directly opens cmd instead of PowerShell]
   
4. Run the command
   

for %i in (*.mp4) do ffmpeg -i "%i" "%~ni.mp3"

If you want to put this into a batch file on Windows 10, you need to use %%i.

A one-line bash script would be easy to do - replace *.avi with your filetype:

for i in *.avi; do ffmpeg -i "$i" -qscale 0 "$(basename "$i" .avi)".mov  ; done

To convert with subdirectories use e.g.

find . -exec ffmpeg -i {} {}.mp3 \;

@Linux To convert a bunch, my one liner is this, as example (.avi to .mkv) in same directory:

for f in *.avi; do ffmpeg -i "${f}" "${f%%.*}.mkv"; done

please observe the double "%%" in the output statement. It gives you not only the first word or the input filename, but everything before the last dot.

For anyone who wants to batch convert anything with ffmpeg but would like to have a convenient Windows interface, I developed this front-end:

https://sourceforge.net/projects/ffmpeg-batch

It adds to ffmpeg a window fashion interface, progress bars and time remaining info, features I always missed when using ffmpeg.

Of course, now PowerShell has come along, specifically designed to make something exactly like this extremely easy.

And, yes, PowerShell is also available on other operating systems other than just Windows, but it comes pre-installed on Windows, so this should be useful to everyone.

First, you'll want to list all of the files within the current directory, so, we'll start off with:

ls

You can also use ls -Recurse if you want to recursively convert all files in subdirectories too.

Then, we'll filter those down to only the type of file we want to convert - e.g. "avi".

ls | Where { $_.Extension -eq ".avi" }

After that, we'll pass that information to FFmpeg through a ForEach.

For FFmpeg's input, we will use the FullName - that's the entire path to the file. And for FFmpeg's output we will use the Name - but replacing the .avi at the end with .mp3. So, it will look something like this:

$_.Name.Replace(".avi", ".mp3")

So, let's put all of that together and this is the result:

ls | Where { $_.Extension -eq ".avi" } | ForEach { ffmpeg -i $_.FullName $_.Name.Replace(".avi", ".mp3") }

That will convert all ".avi" files into ".mp3" files through FFmpeg, just replace the three things in quotes to decide what type of conversion you want, and feel free to add any other arguments to FFmpeg within the ForEach.

You could take this a step further and add Remove-Item to the end to automatically delete the old files.

If ffmpeg isn't in your path, and it's actually in the directory you're currently in, write ./ffmpeg there instead of just ffmpeg.

Hope this helps anyone.

Using multiple cores, this is the fastest way, (using parallel):

parallel "ffmpeg -i {1} {1.}.mp4" ::: *.avi 

If you have GNU parallel you could convert all .avi files below vid_dir to mp4 in parallel, using all except one of your CPU cores with

find vid_dir -type f -name '*.avi' -not -empty -print0 |
    parallel -0 -j -1 ffmpeg -loglevel fatal -i {} {.}.mp4

To convert from/to different formats, change '*.avi' or .mp4 as needed. GNU parallel is listed in most Linux distributions' repositories in a package which is usually called parallel.

I know this might be redundant but I use this script to batch convert files.

old_extension=$1
new_extension=$2

for i in *."$old_extension";
  do ffmpeg -i "$i" "${i%.*}.$new_extension";
done

It takes 2 arguments to make it more flexible :

1. the extension you want to convert from
2. the new extension you want to convert to

I create an alias for it but you can also use it manually like this:

sh batch_convert.sh mkv mp4

This would convert all the mkv files into mp4 files.

As you can see it slightly more versatile. As long as ffmpeg can convert it you can specify any two extensions.

The following script works well for me in a Bash on Windows (so it should work just as well on Linux and Mac). It addresses some problems I have had with some other solutions:

• Processes files in subfolders
• Replaces the source extension with the target extension instead of just appending it
• Works with files with multiple spaces and multiple dots in the name (See this answer for details.)
• Can be run when the target file exists, prompting before overwriting

ffmpeg-batch-convert.sh:

sourceExtension=$1 # e.g. "mp3"
targetExtension=$2 # e.g. "wav"
IFS=$'\n'; set -f
for sourceFile in $(find . -iname "*.$sourceExtension")
do
    targetFile="${sourceFile%.*}.$targetExtension"
    ffmpeg -i "$sourceFile" "$targetFile"
done
unset IFS; set +f

Example call:

$ sh ffmpeg-batch-convert.sh mp3 wav

As a bonus, if you want the source files deleted, you can modify the script like this:

sourceExtension=$1 # e.g. "mp3"
targetExtension=$2 # e.g. "wav"
deleteSourceFile=$3 # "delete" or omitted
IFS=$'\n'; set -f
for sourceFile in $(find . -iname "*.$sourceExtension")
do
    targetFile="${sourceFile%.*}.$targetExtension"
    ffmpeg -i "$sourceFile" "$targetFile"
    if [ "$deleteSourceFile" == "delete" ]; then
        if [ -f "$targetFile" ]; then
            rm "$sourceFile"
        fi
    fi
done
unset IFS; set +f

Example call:

$ sh ffmpeg-batch-convert.sh mp3 wav delete

If one wants to convert all the files matching several possible extensions in an entire directory with ffmpeg on linux or macos, one can use the following command:

for i in *.{avi,mkv,mov,mp4,webm}; do ffmpeg -i "$i" "${i%.*}.wav"; done

(I extended llogan's answer to support several possible file extensions, as in my case I had to convert all videos files into .wav regardless of the video type.)

To view the results, one can list the total number of files broken down by specific extension with this command by squozen:

find . -type f | sed 's/.*\.//' | sort | uniq -c

e.g.:

    176 mkv
    417 wav
    241 webm

Since 241 + 176 = 417, all video files were converted to .wav files.

In case one wants to transcribe all these videos, see How do I run Whisper on an entire directory?

Getting a bit like code golf here, but since nearly all the answers so far are bash (barring one lonely cmd one), here's a windows cross-platform command that uses powershell (because awesome):

ls *.avi|%{ ffmpeg -i $_ <ffmpeg options here> $_.name.replace($_.extension, ".mp4")}

You can change *.avi to whatever matches your source footage.

Also if you want same convertion in subfolders. here is the recursive code.

for /R "folder_path" %%f in (*.mov,*.mxf,*.mkv,*.webm) do (
    ffmpeg.exe -i "%%~f" "%%~f.mp4"
    )

I use this for add subtitle for Tvshows or Movies on Windows.

Just create "subbed" folder and bat file in the video and sub directory.Put code in bat file and run.

for /R  %%f in (*.mov,*.mxf,*.mkv,*.webm) do (
    ffmpeg.exe  -i "%%~f" -i "%%~nf.srt" -map 0:v -map 0:a -map 1:s -metadata:s:a language=eng -metadata:s:s:1 language=tur -c copy ./subbed/"%%~nf.mkv"
    )

For giggles, here's solution in fish-shell:

for i in *.avi; ffmpeg -i "$i" (string split -r -m1 . $i)[1]".mp4"; end

Alternative approach using fd command (repository):

cd directory
fd -d 1 mp3 -x ffmpeg -i {} {.}.wav

-d means depth

-x means execute

{.} path without file extension

for i in *.flac;
  do name=`echo "${i%.*}"`;
  echo $name;
  ffmpeg -i "${i}" -ab 320k -map_metadata 0 -id3v2_version 3 "${name}".mp3;
done

Batch process flac files into mp3 (safe for file names with spaces) using [1] [2]

windows:

@echo off
for /r %%d in (*.wav) do (
    ffmpeg -i "%%~nd%%~xd" -codec:a libmp3lame -c:v copy -qscale:a 2 "%

%~nd.2.mp3"
)

this is variable bitrate of quality 2, you can set it to 0 if you want but unless you have a really good speaker system it's worthless imo

I'm using this one-liner in linux to convert files (usually H265) into something I can play on Kodi without issues:

for f in *.mkv; do ffmpeg -i "$f" -c:v libx264 -crf 28 -c:a aac -b:a 128k output.mkv; mv -f output.mkv "$f"; done

This converts to a temporary file and then replaces the original so the names remain the same after conversion.

I developed a python package for this case.

https://github.com/developer0hye/BatchedFFmpeg

You can easily install and use it.

pip install batchedffmpeg
batchedffmpeg * -i folder * output_file

Only this one Worked for me, pls notice that you have to create "newfiles" folder manually where the ffmpeg.exe file is located.

Convert . files to .wav audio Code:

for %%a in ("*.*") do ffmpeg.exe -i "%%a" "newfiles\%%~na.wav"
pause

i.e if you want to convert all .mp3 files to .wav change ("*.*") to ("*.mp3").

The author of this script is :

https://forum.videohelp.com/threads/356314-How-to-batch-convert-multiplex-any-files-with-ffmpeg

Another simple solution that hasn't been suggested yet would be to use xargs:

ls *.avi | xargs -i -n1 ffmpeg -i {} "{}.mp4"

One minor pitfall is the awkward naming of output files (e.g. input.avi.mp4). A possible workaround for this might be:

ls *.avi | xargs -i -n1 bash -c "i={}; ffmpeg -i {} "\${i%.*}.mp4""

This will create mp4 video from all the jpg files from current directory.

echo exec("ffmpeg -framerate 1/5 -i photo%d.jpg -r 25 -pix_fmt yuv420p output.mp4");

I needed all the videos to use the same codec for merging purposes
so this conversion is mp4 to mp4
it's in zsh but should easily be convertible to bash

for S (*.mp4) { ffmpeg -i $S -c:v libx264 -r 30  new$S }

Bash is terrible to me, so under Linux/Mac, I prefer Ruby script:

( find all the files in a folder and then convert it from rmvb/rm format to mp4 format )

# filename: run.rb
Dir['*'].each{ |rm_file|
  next if rm_file.split('.').last == 'rb'
  command = "ffmpeg -i '#{rm_file}' -c:v h264 -c:a aac '#{rm_file.split('.')[0]}.mp4'"
  puts "== command: #{command}"
  `#{command}`
}

and you can run it with: ruby run.rb

This one script finds and converts any files that ffmpeg supports (no need to specify only one type):

find . \( -name "*.3dostr" -o -name "*.3g2" -o -name "*.3gp" -o -name "*.aa" -o -name "*.aac" -o -name "*.ac3" -o -name "*.acm" -o -name "*.act" -o -name "*.adf" -o -name "*.adp" -o -name "*.ads" -o -name "*.adts" -o -name "*.afc" -o -name "*.aiff" -o -name "*.aix" -o -name "*.alp" -o -name "*.amr" -o -name "*.amrnb" -o -name "*.amrwb" -o -name "*.anm" -o -name "*.apc" -o -name "*.ape" -o -name "*.apm" -o -name "*.apng" -o -name "*.aptx" -o -name "*.aqtitle" -o -name "*.asf" -o -name "*.asf_o" -o -name "*.asf_stream" -o -name "*.ass" -o -name "*.ast" -o -name "*.au" -o -name "*.av1" -o -name "*.avi" -o -name "*.avisynth" -o -name "*.avm2" -o -name "*.avr" -o -name "*.avs" -o -name "*.avs2" -o -name "*.bethsoftvid" -o -name "*.bfi" -o -name "*.bfstm" -o -name "*.bin" -o -name "*.bink" -o -name "*.bit" -o -name "*.bmv" -o -name "*.boa" -o -name "*.brstm" -o -name "*.c93" -o -name "*.caf" -o -name "*.cavsvideo" -o -name "*.cdg" -o -name "*.cdxl" -o -name "*.cine" -o -name "*.codec2" -o -name "*.codec2raw" -o -name "*.concat" -o -name "*.crc" -o -name "*.dash" -o -name "*.data" -o -name "*.daud" -o -name "*.dcstr" -o -name "*.dds_pipe" -o -name "*.derf" -o -name "*.dfa" -o -name "*.dhav" -o -name "*.dirac" -o -name "*.dnxhd" -o -name "*.dsf" -o -name "*.dshow" -o -name "*.dsicin" -o -name "*.dss" -o -name "*.dts" -o -name "*.dtshd" -o -name "*.dv" -o -name "*.dvbsub" -o -name "*.dvbtxt" -o -name "*.dvd" -o -name "*.dxa" -o -name "*.ea" -o -name "*.eac3" -o -name "*.epaf" -o -name "*.f32be" -o -name "*.f32le" -o -name "*.f4v" -o -name "*.f64be" -o -name "*.f64le" -o -name "*.ffmetadata" -o -name "*.fifo" -o -name "*.filmstrip" -o -name "*.fits" -o -name "*.flac" -o -name "*.flic" -o -name "*.flv" -o -name "*.framecrc" -o -name "*.framehash" -o -name "*.framemd5" -o -name "*.frm" -o -name "*.fsb" -o -name "*.fwse" -o -name "*.g722" -o -name "*.g723_1" -o -name "*.g726" -o -name "*.g726le" -o -name "*.g729" -o -name "*.gdigrab" -o -name "*.gdv" -o -name "*.genh" -o -name "*.gif" -o -name "*.gif_pipe" -o -name "*.gsm" -o -name "*.gxf" -o -name "*.h261" -o -name "*.h263" -o -name "*.h264" -o -name "*.hash" -o -name "*.hca" -o -name "*.hcom" -o -name "*.hds" -o -name "*.hevc" -o -name "*.hls" -o -name "*.hnm" -o -name "*.ico" -o -name "*.idcin" -o -name "*.idf" -o -name "*.iff" -o -name "*.ifv" -o -name "*.ilbc" -o -name "*.image2" -o -name "*.image2pipe" -o -name "*.ingenient" -o -name "*.ipmovie" -o -name "*.ipod" -o -name "*.ircam" -o -name "*.ismv" -o -name "*.iss" -o -name "*.iv8" -o -name "*.ivf" -o -name "*.ivr" -o -name "*.j2k_pipe" -o -name "*.jacosub" -o -name "*.jpeg_pipe" -o -name "*.jpegls_pipe" -o -name "*.jv" -o -name "*.kux" -o -name "*.kvag" -o -name "*.latm" -o -name "*.lavfi" -o -name "*.libopenmpt" -o -name "*.live_flv" -o -name "*.lmlm4" -o -name "*.loas" -o -name "*.lrc" -o -name "*.lvf" -o -name "*.lxf" -o -name "*.m4v" -o -name "*.matroska" -o -name "*.webm" -o -name "*.mcc" -o -name "*.md5" -o -name "*.mgsts" -o -name "*.microdvd" -o -name "*.mjpeg" -o -name "*.mjpeg_2000" -o -name "*.mkvtimestamp_v2" -o -name "*.mlp" -o -name "*.mlv" -o -name "*.mm" -o -name "*.mmf" -o -name "*.mov" -o -name "*.mp4" -o -name "*.m4a" -o -name "*.3gp" -o -name "*.3g2" -o -name "*.mj2" -o -name "*.mp2" -o -name "*.mp3" -o -name "*.mp4" -o -name "*.mpc" -o -name "*.mpc8" -o -name "*.mpeg" -o -name "*.mpeg1video" -o -name "*.mpeg2video" -o -name "*.mpegts" -o -name "*.mpegtsraw" -o -name "*.mpegvideo" -o -name "*.mpjpeg" -o -name "*.mpl2" -o -name "*.mpsub" -o -name "*.msf" -o -name "*.msnwctcp" -o -name "*.mtaf" -o -name "*.mtv" -o -name "*.mulaw" -o -name "*.musx" -o -name "*.mv" -o -name "*.mvi" -o -name "*.mxf" -o -name "*.mxf_d10" -o -name "*.mxf_opatom" -o -name "*.mxg" -o -name "*.nc" -o -name "*.nistsphere" -o -name "*.nsp" -o -name "*.nsv" -o -name "*.null" -o -name "*.nut" -o -name "*.nuv" -o -name "*.oga" -o -name "*.ogg" -o -name "*.ogv" -o -name "*.oma" -o -name "*.opus" -o -name "*.paf" -o -name "*.pam_pipe" -o -name "*.pbm_pipe" -o -name "*.pcx_pipe" -o -name "*.pgm_pipe" -o -name "*.pgmyuv_pipe" -o -name "*.pgx_pipe" -o -name "*.pictor_pipe" -o -name "*.pjs" -o -name "*.pmp" -o -name "*.png_pipe" -o -name "*.pp_bnk" -o -name "*.ppm_pipe" -o -name "*.psd_pipe" -o -name "*.psp" -o -name "*.psxstr" -o -name "*.pva" -o -name "*.pvf" -o -name "*.qcp" -o -name "*.qdraw_pipe" -o -name "*.r3d" -o -name "*.rawvideo" -o -name "*.realtext" -o -name "*.redspark" -o -name "*.rl2" -o -name "*.rm" -o -name "*.roq" -o -name "*.rpl" -o -name "*.rsd" -o -name "*.rso" -o -name "*.rtp" -o -name "*.rtp_mpegts" -o -name "*.rtsp" -o -name "*.s16be" -o -name "*.s16le" -o -name "*.s24be" -o -name "*.s24le" -o -name "*.s32be" -o -name "*.s32le" -o -name "*.s337m" -o -name "*.s8" -o -name "*.sami" -o -name "*.sap" -o -name "*.sbc" -o -name "*.sbg" -o -name "*.scc" -o -name "*.sdl" -o -name "*.sdl2" -o -name "*.sdp" -o -name "*.sdr2" -o -name "*.sds" -o -name "*.sdx" -o -name "*.segment" -o -name "*.ser" -o -name "*.sgi_pipe" -o -name "*.shn" -o -name "*.siff" -o -name "*.singlejpeg" -o -name "*.sln" -o -name "*.smjpeg" -o -name "*.smk" -o -name "*.smoothstreaming" -o -name "*.smush" -o -name "*.sol" -o -name "*.sox" -o -name "*.spdif" -o -name "*.spx" -o -name "*.srt" -o -name "*.stl" -o -name "*.stream_segment" -o -name "*.ssegment" -o -name "*.streamhash" -o -name "*.subviewer" -o -name "*.subviewer1" -o -name "*.sunrast_pipe" -o -name "*.sup" -o -name -o -name "*.svag" -o -name "*.svcd" -o -name "*.svg_pipe" -o -name "*.swf" -o -name "*.tak" -o -name "*.tedcaptions" -o -name "*.tee" -o -name "*.thp" -o -name "*.tiertexseq" -o -name "*.tiff_pipe" -o -name "*.tmv" -o -name "*.truehd" -o -name "*.tta" -o -name "*.tty" -o -name "*.txd" -o -name "*.ty" -o -name "*.u16be" -o -name "*.u16le" -o -name "*.u24be" -o -name "*.u24le" -o -name "*.u32be" -o -name "*.u32le" -o -name "*.u8" -o -name "*.uncodedframecrc" -o -name "*.v210" -o -name "*.v210x" -o -name "*.vag" -o -name "*.vc1" -o -name "*.vc1test" -o -name "*.vcd" -o -name "*.vfwcap" -o -name "*.vidc" -o -name "*.vividas" -o -name "*.vivo" -o -name "*.vmd" -o -name "*.vob"  -o -name "*.vobsub" -o -name "*.voc" -o -name "*.vpk" -o -name "*.vplayer" -o -name "*.vqf" -o -name "*.w64" -o -name "*.wav" -o -name "*.wc3movie" -o -name "*.webp_pipe" -o -name "*.webvtt" -o -name "*.wsaud" -o -name "*.wsd" -o -name "*.wsvqa" -o -name "*.wtv" -o -name "*.wv" -o -name "*.wve" -o -name "*.xa" -o -name "*.xbin" -o -name "*.xmv" -o -name "*.xpm_pipe" -o -name "*.xvag" -o -name "*.xwd_pipe" -o -name "*.xwma" -o -name "*.yop" -o -name "*.yuv4mpegpipe" \) -exec sh -c 'ffmpeg -n -i "$0" -vn -q:a 0 "${0%.*}.mp3"' {} \;

Replace the last command with 'ffmpeg -n -i "$0" -vn -q:a 0 "${0%.*}.mp3" && rm "$0"' to delete the original after the conversion

P.S: for the record, that list is as follows:

*.3gp, *.aa, *.aac, *.ac3, *.acm, *.act, *.adf, *.adp, *.ads, *.adts, *.afc, *.aiff, *.aix, *.alp, *.amr, *.amrnb, *.amrwb, *.anm, *.apc, *.ape, *.apm, *.apng, *.aptx, *.aqtitle, *.asf, *.asf_o, *.asf_stream, *.ass, *.ast, *.au, *.av1, *.avi, *.avisynth, *.avm2, *.avr, *.avs, *.avs2, *.bethsoftvid, *.bfi, *.bfstm, *.bin, *.bink, *.bit, *.bmv, *.boa, *.brstm, *.c93, *.caf, *.cavsvideo, *.cdg, *.cdxl, *.cine, *.codec2, *.codec2raw, *.concat, *.crc, *.dash, *.data, *.daud, *.dcstr, *.dds_pipe, *.derf, *.dfa, *.dhav, *.dirac, *.dnxhd, *.dsf, *.dshow, *.dsicin, *.dss, *.dts, *.dtshd, *.dv, *.dvbsub, *.dvbtxt, *.dvd, *.dxa, *.ea, *.eac3, *.epaf, *.f32be, *.f32le, *.f4v, *.f64be, *.f64le, *.ffmetadata, *.fifo, *.filmstrip, *.fits, *.flac, *.flic, *.flv, *.framecrc, *.framehash, *.framemd5, *.frm, *.fsb, *.fwse, *.g722, *.g723_1, *.g726, *.g726le, *.g729, *.gdigrab, *.gdv, *.genh, *.gif, *.gif_pipe, *.gsm, *.gxf, *.h261, *.h263, *.h264, *.hash, *.hca, *.hcom, *.hds, *.hevc, *.hls, *.hnm, *.ico, *.idcin, *.idf, *.iff, *.ifv, *.ilbc, *.image2, *.image2pipe, *.ingenient, *.ipmovie, *.ipod, *.ircam, *.ismv, *.iss, *.iv8, *.ivf, *.ivr, *.j2k_pipe, *.jacosub, *.jpeg_pipe, *.jpegls_pipe, *.jv, *.kux, *.kvag, *.latm, *.lavfi, *.libopenmpt, *.live_flv, *.lmlm4, *.loas, *.lrc, *.lvf, *.lxf, *.m4v, *.matroska, *.webm, *.mcc, *.md5, *.mgsts, *.microdvd, *.mjpeg, *.mjpeg_2000, *.mkvtimestamp_v2, *.mlp, *.mlv, *.mm, *.mmf, *.mov, *.mp4, *.m4a, *.3gp, *.3g2, *.mj2, *.mp2, *.mp3, *.mpc, *.mpc8, *.mpeg, *.mpeg1video, *.mpeg2video, *.mpegts, *.mpegtsraw, *.mpegvideo, *.mpjpeg, *.mpl2, *.mpsub, *.msf, *.msnwctcp, *.mtaf, *.mtv, *.mulaw, *.musx, *.mv, *.mvi, *.mxf, *.mxf_d10, *.mxf_opatom, *.mxg, *.nc, *.nistsphere, *.nsp, *.nsv, *.null, *.nut, *.nuv, *.oga, *.ogg, *.ogv, *.oma, *.opus, *.paf, *.pam_pipe, *.pbm_pipe, *.pcx_pipe, *.pgm_pipe, *.pgmyuv_pipe, *.pgx_pipe, *.pictor_pipe, *.pjs, *.pmp, *.png_pipe, *.pp_bnk, *.ppm_pipe, *.psd_pipe, *.psp, *.psxstr, *.pva, *.pvf, *.qcp, *.qdraw_pipe, *.r3d, *.rawvideo, *.realtext, *.redspark, *.rl2, *.rm, *.roq, *.rpl, *.rsd, *.rso, *.rtp, *.rtp_mpegts, *.rtsp, *.s16be, *.s16le, *.s24be, *.s24le, *.s32be, *.s32le, *.s337m, *.s8, *.sami, *.sap, *.sbc, *.sbg, *.scc, *.sdl, *.sdl2, *.sdp, *.sdr2, *.sds, *.sdx, *.segment, *.ser, *.sgi_pipe, *.shn, *.siff, *.singlejpeg, *.sln, *.smjpeg, *.smk, *.smoothstreaming, *.smush, *.sol, *.sox, *.spdif, *.spx, *.srt, *.stl, *.stream_segment, *.ssegment, *.streamhash, *.subviewer, *.subviewer1, *.sunrast_pipe, *.sup, *.svag, *.svcd, *.svg_pipe, *.swf, *.tak, *.tedcaptions, *.tee, *.thp, *.tiertexseq, *.tiff_pipe, *.tmv, *.truehd, *.tta, *.tty, *.txd, *.ty, *.u16be, *.u16le, *.u24be, *.u24le, *.u32be, *.u32le, *.u8, *.uncodedframecrc, *.v210, *.v210x, *.vag, *.vc1, *.vc1test, *.vcd, *.vfwcap, *.vidc, *.vividas, *.vivo, *.vmd, *.vob, *.vobsub, *.voc, *.vpk, *.vplayer, *.vqf, *.w64, *.wav, *.wc3movie, *.webp, *.webp_pipe, *.webvtt, *.wsaud, *.wsd, *.wsvqa, *.wtv, *.wv, *.wve, *.xa, *.xbin, *.xmv, *.xpm_pipe, *.xvag, *.xwd_pipe, *.xwma, *.yop, *.yuv4mpegpipe

By calling ffmpeg just once and passing the file names as arguments:

ffmpeg         \
  -i 0.mp4     \
  -i 1.mp4     \
  -i 2.mp4     \
  -map 0 0.avi \
  -map 1 1.avi \
  -map 2 2.avi

where the argument list can be generated in an OS-dependent way. For example, using Z shell:

{
  for in in *.mp4
    print -- -i $in

  i=0
  for out in *.mp4(:s/mp4/avi/:)
    print -- -map $((i++)) $out
} |
  xargs ffmpeg