Doom9's Forum - View Single Post - How to change the framerate of an MP4 file without re-encoding video?

MikeBell · 22nd January 2016, 01:21

My previous post ended up in moderation queue because I quoted StainlessS's post with lots of links

Anyway, abreviation:

raffriff42: I tried this:

Code:

ffmpeg -i out.m4a -filter:a "atempo=0.5" -vn outputaudio.aac
same as:
ffmpeg -i source.mp4 -filter_complex "[0:a]atempo=0.5[a]" -map "[a]" outputaud.m4a

and it sounded horrible. While the speed sounded correct, it had that metallic echo all over it. Couldn't understand anything. It sounded nothing like VLC's 0.5x slowdown. Note: I used 0.5 and not 2.0 like in your example because I wanted it to slow down, not speed up by 2x.

StainlessS: I always try changing AR like this... without re-encoding. Most of the time it works great:

Code:

 ffmpeg -i in.mp4 -vcodec copy -acodec copy -aspect 16:9 output.mp4

22nd January 2016, 01:21	#5 \| Link
MikeBell Registered User Join Date: Jan 2004 Posts: 7	My previous post ended up in moderation queue because I quoted StainlessS's post with lots of links Anyway, abreviation: raffriff42: I tried this: Code: ffmpeg -i out.m4a -filter:a "atempo=0.5" -vn outputaudio.aac same as: ffmpeg -i source.mp4 -filter_complex "[0:a]atempo=0.5[a]" -map "[a]" outputaud.m4a and it sounded horrible. While the speed sounded correct, it had that metallic echo all over it. Couldn't understand anything. It sounded nothing like VLC's 0.5x slowdown. Note: I used 0.5 and not 2.0 like in your example because I wanted it to slow down, not speed up by 2x. StainlessS: I always try changing AR like this... without re-encoding. Most of the time it works great: Code: ffmpeg -i in.mp4 -vcodec copy -acodec copy -aspect 16:9 output.mp4