How do I rotate a video without audio alteration?

Question

I have a video recorded with an iPad, and I want to rotate it.

I tried the solution provided in this answer, but first I get this warning :

If the file is using B-frames as reference, this can lead to a crash or stuttering. Avidemux can use another mode which is safe but YOU WILL LOSE FRAME ACCURACY. Do you want to use that mode?

I tried with both No and Yes to that question above, and with MPEG-4 AVC for the video output, and "AVI" as the format. However the resulting video's audio is messed up, even though I just used "Copy" for the audio stream.

The audio becomes very choppy, inintelligible.

What settings should I use then ?

Info about the source video :

• Container : Quicktime
• Video codec : H.264
• Audio codec : MPEG-4 AAC

Answer 1

Try to use mp3 audio codec. I don't know how to do that with Avidemux, but this is what worked for me when converting various videos to mp4 which is accepted by youtube and works well on various platforms:

ffmpeg -i Windup-demo-2.5.0.ogv -acodec libmp3lame -vcodec libx264 -crf 18 Windup-demo-2.5.0.mp4

To get the libmp3lame codec I had to install the lame library:

sudo apt-get install libmp3lame0  ## Ubuntu 14.04

For rotating, use -vf transpose=2 (-90 deg; for +90, use ...=1).

ffmpeg ... -i input.mov -vf transpose=2 -acodec libmp3lame output.mp4

Note that the order of the params matter.