sửa lại lệnh cho đúng: @ECHO OFF
Setlocal EnableDelayedExpansion
set INPUT=C:\input
set OUTPUT=C:\output

set /a bitrate_step=100

for %%a in ("%INPUT%\*.mp4") DO (
    set "current_bitrate=0"
    for /L %%i in (1,1,10) DO (
        set /a current_bitrate+=bitrate_step
        ffmpeg -i "%%a" -vcodec libx264 -pix_fmt yuv420p -g 60 -r 30 -b:v !current_bitrate!k -acodec libmp3lame -b:a 128k -ar 48000 -metadata title="Test Title" -metadata subtitle="Test Subtitle" -metadata rating="5" -metadata comments="#trending" -metadata artist="" -metadata album_artist="" -metadata album="" -metadata date="" -metadata track="" -metadata genre="" -metadata publisher="" -metadata encoded_by="" -metadata copyright="" -metadata composer="" -metadata performer="" -metadata TIT1="" -metadata TIT3="" -metadata disc="" -metadata TKEY="" -metadata TBPM="" -metadata language="eng" -metadata encoder="" -preset superfast "%OUTPUT%\output%%i_%%~na.mp4"
    )
)
