[FFmpeg-user] questions about audio filter "atempo"

[Pavel Koshevoy]

On 7/17/2012 9:58 PM, 韩瑞松 wrote:
> Why did I get a "Segmentation fault"?
> I used this command line:
> ffmpeg -y -i youku.mp4 -analyzeduration 2G -vcodec libx264 -b 512k -r 25 -s 576x312 -aspect 576:312 -psnr -acodec libfaac -ab 64k -ar 44100 -ac 2 -vf "movie=2.jpg,scale=100:100[logo];[in][logo]overlay=5:5[out]" -af atempo=2 -f flv -map_chapters -1 -g 50 youku.mp4.flv
> it's output:

A stack trace would be helpful.

When you set atempo=2 you double the audio playback rate and cut down 
the soundtrack duration in half. However, this does not affect the video 
track. You need to adjust the video track rate to match the audio track.

I haven't tried this myself, but you probably need to use setpts filter 
for the video track (try setpts=0.5*PTS).

http://ffmpeg.org/trac/ffmpeg/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video
http://ffmpeg.org/ffmpeg.html#setpts

Pavel.