Video batch files.

[pandy]

Some cosmetic:

scale=640:trunc(ow/a/2)*2

can be replaced by

scale=640:-2

(modulo 2 = -2, modulo 16=-16 ...).
Simpler way for normalization is peak2peak -3.0103dBFS - safest and fastest and at the same only 0.5 bit loss (best DAC dynamic range usage).

[pcspeak]

It's been a while since I posted.
This deals with MKV videos. To extract only the English streams.
The batch file, ffmpeg.exe and your MKV videos go in the one folder
Run the batch file. Output in NEW\

Usually the first stream is a video, the second, to however many are audio, and the last subtitles, if any.
The first pass copies the file, setting the video language tag to English. It may already be.
The second pass copies only the English video+audio streams.
There will be no audio in the output if the language tag is not set to English for the audio stream.
It usually is, as the video tag is now.

@echo off
if not exist NEW\*.* md NEW
if exist temp\*.* (del /q temp\*.*) else md temp

for %%a in ("*.mkv") do call :Process "%%a"
goto :end

:Process
:: Set the first stream, normally the video, to English. (In case it's not.)
ffmpeg -i "%~1" -vcodec copy -acodec copy -metadata:s:0 language=eng -y "temp\%~1"
:: Copy the English streams (video+audio) to a new video.
ffmpeg -i "temp\%~1" -vcodec copy -acodec copy -map 0:m:language:eng -y "NEW\%~1"
goto :eof

:end
rd /s /q temp

Warning! There be Dragons.
I do not have a single MKV with multiple audio tracks.
For testing I used videos with only an English audio track.

Cheers.

Edit:
Change the first ffmpeg pass to the following to set the first TWO streams to English if you wish to try that.
Hopefully they'll be the English video and audio streams.

ffmpeg -i "%~1" -vcodec copy -acodec copy -metadata:s:0 language=eng -metadata:s:1 language=eng -y "temp\%~1"

[pcspeak]

Should give a list of MKV videos that do NOT have an English audio track tagged.
A work in progress.
The batch file, MediaInfo.exe(command line version) and your MKV videos go in the one folder.
Run the batch file.

The output format is:
video file name#language/language/language

@echo off
if exist NoEnglish-List.txt del /q NoEnglish-List.txt
if exist temp*.* del /q temp*.*

for %%a in ("*.mkv") do call :Process "%%a"

echo List of All videos with NO Englist audio track defined in the file's METADATA > NoEnglish-List.txt
echo Does NOT mean there is no English audio track!!! >> NoEnglish-List.txt

:: Find videos with NO English defined.
find /v "English" temp2.txt >> NoEnglish-List.txt
del /q temp*.*
goto end

:Process
setlocal
set video=%~1
mediainfo.exe "--Inform=General;%%Audio_Language_List%%" "%video%" > temp.txt
set /p Languages= < temp.txt
del temp.txt
echo "%video%"#%Languages% >> temp2.txt
endlocal
goto :eof

:end
start /i NoEnglish-List.txt

Cheers.