How to Rotate or Flip a Video in Avidemux (90°, 180°, Arbitrary Angle)

Rotating a video means changing the direction of the pixels in every frame — for example turning a sideways landscape clip into an upright portrait clip. In Avidemux, you do this with the Rotate or Arbitrary Rotate video filters (found under Video > Filters > Transform). Rotating changes the actual pixel data, so the output must be re-encoded — it cannot be done in Copy mode.

Key requirement: under Video Output, select a real encoder (for example Mpeg4 AVC (x264)), not Copy. Filters are disabled entirely while Copy mode is active.

Step-by-step: rotate a video in Avidemux

  1. Open your video via File > Open (or drag the file onto the window).
  2. Set Video Output to an encoder. Choose Mpeg4 AVC (x264) for H.264 output, or Mpeg4 ASP (xvid4) if you want a simple MPEG-4 file. Leave Audio Output on Copy (audio is unaffected by rotation) and Output Format on MP4 Muxer.
  3. Open the filter manager: go to Video > Filters.
  4. Add the Rotate filter: in the left list, open the Transform category, select Rotate, and click the green plus button.
  5. Pick an angle: the Rotate filter offers 90°, 180°, or 270° turns. Choose the one that makes the preview look correct. (For mirror/flip effects, use the Flip or Mirror filters in the same Transform category.)
  6. Need an arbitrary angle? In the 2.8.x line, the Arbitrary Rotate filter lets you type any angle, with an option to fill the exposed edges. Note: because the frame corners now stick out, the output frame is typically cropped or padded — expect slight quality trade-offs at odd angles (see the FAQ below).
  7. Click OK, then save: press OK in the filter manager, then File > Save, give the file a name ending in .mp4, and wait for the encoding to finish.

Rotate vs. the MP4 rotation flag (no re-encoding)

There are two completely different ways a video can be “rotated”:

MethodWhat changesRe-encoding needed?
Pixel rotation (Avidemux Rotate filter)The pixels of every frame are rewritten; the video itself is upright.Yes — quality depends on the encoder settings you choose.
MP4 rotation metadata flagOnly a number in the file header (e.g. rotate=90); players are told to display the frame turned. The pixels never change.No — instant, lossless.

Avidemux cannot set the rotation metadata flag — it has no option to write it. If you only want players to display the video turned (for example a phone video that plays sideways), use ffmpeg instead:

ffmpeg -i input.mp4 -c copy -metadata:s:v rotate=90 output.mp4

This copies every stream untouched (-c copy), so there is zero quality loss and it takes seconds. The catch: some players and social apps ignore the rotation flag, in which case only a real pixel rotation (Avidemux) will display correctly everywhere. A quick compatibility test: open the flagged file in two or three different players before sharing it.

Which to choose? If you need the video to be upright everywhere — including editors, browsers, and uploads — do a pixel rotation in Avidemux. If it is only for your own viewing and your players respect the flag, the ffmpeg one-liner is the fastest fix.

Frequently asked questions

Will rotating a video in Avidemux reduce its quality?

Slightly, yes — rotation requires re-encoding, and any lossy re-encode loses a little detail. The loss is negligible at sane settings: use Mpeg4 AVC (x264) with a reasonable quality preset and keep the resolution unchanged. To avoid any loss, use the ffmpeg rotation-flag method above, which copies the streams untouched.

How do I fix a portrait phone video that plays sideways?

Open it in Avidemux, set Video Output to an encoder (not Copy), add Video > Filters > Transform > Rotate, and pick the 90° or 270° option that makes the preview upright. Save as a new MP4. Phone-recorded clips usually just need one 90° turn; which direction depends on how you held the phone, so check the preview.

Can I rotate by an arbitrary angle, like 15°?

Yes — the 2.8.x line includes an Arbitrary Rotate filter (Video > Filters > Transform) where you type any angle. Keep in mind that at non-90° angles the corners get cropped or padded, and the exposed background is filled with black (or the color you choose), so it is best suited to correcting small tilts rather than large turns.

Why is the Rotate option greyed out in my Avidemux?

The most common cause is Video Output being set to Copy: filters cannot run in Copy mode. Switch Video Output to an encoder such as Mpeg4 AVC (x264) and the Filters menu will become active. (Exact menu wording can vary slightly between builds; the Transform category has carried these filters through the 2.8.x line.)