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After having read this page, I'm using avconv (which in this case is apparently same as ffmpeg, and which I need to use instead since I'm on Ubuntu trusty) to speed up a .swf video.

I don't want a quality loss (not interested in compression), just a visual speed-up.

avconv -i input.swf -filter:v "setpts=0.5*PTS" output.swf

results in quality loss. how do I prevent that?

I don't see why this occurs, mplayer -af scaletempo -speed 1.7 myvideo.swf plays it fine.

From reading this page I tried

avconv -i input.mkv -filter:v "setpts=0.5*PTS" -b 1080 output.mkv

But it didn't help.

llogan
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Alexandre Holden Daly
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2 Answers2

2

its can be tricky if you also want to scale audio too, for example you want to make it 10% slower (110 or 1.1)

*for audio its 1/1.1=0.90909..

avconv -i input.webm -c copy -map 0:0 v.webm
avconv -i input.webm -c copy -map 0:1 a.webm
avconv -i a.webm -acodec libmp3lame a.mp3
avconv -i v.webm -vf setpts=1.1*PTS v2.webm
sox a.mp3 a2.mp3 speed 0.90909
avconv -i a2.mp3 a2.webm
avconv -i a2.webm -i v2.webm -c copy output.webm
Ivan Malyshev
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2

Gotcha!

avconv -i HTSA2-copy.swf -filter:v "setpts=0.5*PTS" -b 12000k -s 1080x1080 Sped_up-setpts=0.5*PTS-HTSA2.swf

the -b and -s parameter values might be overkill haha, but it gets me what I wanted.

Alexandre Holden Daly
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