批量：压缩+moov前置流式MP4，输出compress_xxx.mp4
Get-ChildItem *.mp4 | ForEach-Object {
$src = $_.FullName
$dst = Join-Path $_.DirectoryName ("compress_" + $_.Name)
# crf 24平衡体积画质，数字越大压缩越强、画质略降；音频固定128k aac
ffmpeg -i "$src" `
-c:v libx264 -preset fast -crf 24 -pix_fmt yuv420p `
-c:a aac -b:a 128k `
-movflags +faststart -y "$dst"
}