@echo off
Setlocal EnableDelayedExpansion
set "shag=29"
for /l %%a in (0, !shag!, 1499) do (
rem ffmpeg -ss [старт] -i in.mp4 -t [продолжительность] -map 0 -c copy out.mp4
rem -ss specifies the start time, e.g. 00:01:23.000 or 83 (in seconds)
rem set /A "end = %%a + !shag!"
rem echo [%%a, !end!]
echo %%~a, !shag!
)
pause