[FFmpeg-user] Rotating webm videos

[Rex East]

Hello,

I am trying rotate some webm videos by 90 degrees, ideally without re-encoding.

I tried this command:

ffmpeg -i input.webm -vf “transpose=1” -t 20 output.webm

But this re-encodes the video (slow) and there is noticeable quality loss.

I also tried this command (which works for mp4) which does not
re-encode but sets flags in the metadata:

ffmpeg -i input.webm -c copy -metadata:s:v:0 rotate=90 output.webm

But this does not do anything (I verified output file is identical to input).

My video was downloaded from youtube with the following command:

youtube-dl https://www.youtube.com/watch?v=1Qsxj-B1UPk -f 313+171

Any ideas? Thank you!