Question

I’m using ffmpeg to convert .avi file into a .png image sequence. This one works just fine:

@ ECHO OFF

FOR %%A IN (*.avi) DO CALL :avi2png "%%A"

:avi2png
ffmpeg.exe -y -i %* -sameq -f image2 -c:v png "%%03d.png"

ECHO.
GOTO :EOF

---

But I want the script to extract the name without the extension from .avi file that is currently being processed. This is what the image sequence should look like: currentavi001.png, currentavi002.png etc. The script I came up with isn’t working:

@ ECHO OFF

FOR %%A IN (*.avi) DO CALL :avi2png "%%A"

:avi2png
ffmpeg.exe -y -i %* -sameq -f image2 -c:v png "%%~nA%%03d.png"

ECHO.
GOTO :EOF

---

I’ve tried both %~nA and %%~nA, but to no avail. The script returns this:

Couldn't open file : 
av_interleaved_write_frame(): Input/output error.

I’m a complete layman and would welcome every bit of help.

Answer 1

You can’t refer to the %%A variable in :avi2png. Try this:

@ ECHO OFF

set count=0
FOR %%A IN (*.avi) DO CALL :avi2png "%%A"
goto :eof

:avi2png
set /a count=count+1
set Ncount=00%count%
set Ncount=%Ncount:~-3%
ffmpeg.exe -y -i %* -sameq -f image2 -c:v png "%~n1%Ncount%.png"

ECHO.
GOTO :EOF

If you have one file in the current directory named my_movie.avi ffmpeg will create the png my_movie001.png.

When you call a label from a for loop, you can no longer use your original for loop variable (in this case %%A), instead :label is treated as a separate batch file and all variables on the line after the :label are treated as switches passed to a batch file.

So this…

Call :label one two thee

…works with this…

:label
Echo %1, %2, %3.

…to produce output like this:

one, two, three.

Just as if it were a stand-alone batch file.

Oh, also %%A and the like are never referred to by %%A%% (or %A%, a totally different variable). If you do that (and %%A==Hello) the result would be Hello%, and likely eat a character somewhere in your code, resulting in bizarre errors.