Directly running the FFmpeg command shown in Youtube-DL log resulted in an error message, with exit code 1: C>ffmpeg -y -loglevel "repeat+info" -i "file:ueoRSzCn4kA.480p+m4a128k.f135.mp4" -i "file:ueoRSzCn4kA.480p+m4a128k.mp4.f140" -c copy -map "0:v:0" -map "1:a:0" "file:ueoRSzCn4kA.480p+m4a128k.temp.mp4" Invalid loglevel "repeat+info". Possible levels are numbers or: "quiet" "panic" "fatal" "error" "warning" "info" "verbose" "debug" C>echo %ERRORLEVEL% 1 Running the same FFmpeg command line, without the problematic  -loglevel "repeat+info"  part, resulted in a successful remux and a watchable file; the remuxer also exited with code 0: C>ffmpeg -y -i "file:ueoRSzCn4kA.480p+m4a128k.f135.mp4" -i "file:ueoRSzCn4kA.480p+m4a128k.mp4.f140" -c copy -map "0:v:0" -map "1:a:0" "...

Properties of common image file formats File format BMP GIF PNG JPEG TIFF PCX TGA Max colors 16M 256 256T 16M 16M 16M 16M Max shades of gray 256 256 65536 256 256 256 256 Color modes 2, 16, 256, 32768, 65536, 16M 2, 4, 8, 16, 32, 64, 128, 256 2, 4, 16, 256, 16M, 256T 16M 16, 256, 16M (4), (8), 16, 256, 16M 256, 65536, 16M Low-color modes 2, 16, 256 2, 4, 8, 16, 32, 64, 128, 256 2, 4, 16, 256 — 16, 256 (4), (8), 16, 256 256 High-color modes 32768, 65536, 16M — 16M, 256T 16M 16M 16M 65536, 16M Gray modes — — 2, 4, 16, 256, 65536 256 2, 256, 65536 2 2, 256 Mono­chrome modes 2 colors 2 colors 2 colors or B&W — B&W B&W B&W Com­pres­sion None, RLE (16/ 256 colors) LZW Deflate JPEG None, CCITT (B&W), Pack­Bits, LZW, JPEG RLE None, RLE Trans­pa­ren­cy (op­tion­al) None Single color Single color, Alpha None None None None Inter­lacing (op­tion­al) None Line order Pixel order Pro­gres­sive None None None Multiple images No Yes, ani­mated No No Yes, pages ...