问题
I posted my original question here. Tried suggested solution. But it does not solve my question.
Here's what I did. Download this video from Youtube as a test. Using ffprobe gives:
Stream #0:0: Video: h264 (High), yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 59.94 fps, 59.94 tbr, 1k tbn, 119.88 tbc (default)
The ffmpeg command I used:
ffmpeg -i Iron_Man_1080p_60fps.mp4 -vf "select='eq(n,0)+if(gt(t-prev_selected_t,1/30.01),1,0)'" -vsync 0 -c:v libx265 -crf 28 -c:a aac -b:a 64k Iron_Man_1080p_60fps_CONVERTED.mp4
ffprobe my output file Iron_Man_1080p_60fps_CONVERTED.mp4:
Stream #0:0(und): Video: hevc (Main) (hev1 / 0x31766568), yuv420p(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 454 kb/s, 20.49 fps, 59.94 tbr, 19001 tbn, 59.94 tbc (default)
As you can see, the fps dropped from 59.94 fps to 20.49 fps.
I'm not sure why the suggested solution does not work.
ffmpeg -i 120.mp4 -vf "select='eq(n,0)+if(gt(t-prev_selected_t,1/30.01),1,0)'" -vsync 0 out.mp4
Perhaps -vf does not set a fixed framerate?
Could someone provide an alternative solution using the -r flag please?
Here's re-stating question:
- Set -r 30 if input fps => 30 fps
- Set -r input_fps if input fps < 30 fps
Thank you!
回答1:
The time_base for the sample video is coarse, so the video is actually VFR. Change the interval to 1/30.5 to keep frames which are just beyond the threshold for 1/30.01
-vf "select='eq(n,0)+if(gt(t-prev_selected_t,1/30.50),1,0)'"
来源：https://stackoverflow.com/questions/59297824/ffmpeg-cli-set-r-30-if-input-30-fps-else-r-to-take-input-fps-if-30-fps