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I have a mpeg4 video at 25fps. This video contains just one static frame. I'm trying to downsample the frame rate to 1fps and convert the video to x246 (mp4).

I ran the following ffmpeg command:

ffmpeg -i vid.avi -acodec aac -ar 32000 -ab 64k -ac 2 \
-vcodec libx264 -strict -2 -y -r 1 -force_key_frames 0 vid.mp4

FFmpeg then drops a lot of frames until it inserts the first keyframe. Sometimes image appears only after 16 or 20 seconds.

I gather ffmpeg doesn't insert a keyframe at very beginning.

Does anyone know how could I take the first frame of vid.avi and use it as the key frame for vid.mp4?

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  • have you tried it without -force_key_frames 0? Also might want to try changing the 0 to a 1 to have it start on the first frame instead -force_key_frames 1 – Travis Crum Oct 3 '12 at 14:36
  • yes, i tried without -force_key_frames 0 and with -force_key_frames 1, but that didn't help. I'm pretty stuck. – bodacydo Oct 3 '12 at 18:19
  • is doing it exactly this way required? I'm going to take a wild guess and assume the following: the audio is the focus of the video. The image isn't a huge concern. Sooo couldn't you extract an mp3 from the video (lossless quality of course) and then, acquire the image, maybe even a screenshot if you're that desperate, then create a new video in ffmpeg using the extracted mp3 and image with the fps set to 1? – Travis Crum Oct 3 '12 at 20:06
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    The force_key_frames syntax for using the frame number is -force_key_frames "expr:eq(n,0)" – robd Jul 28 '13 at 21:08
  • I'm fairly sure the root issue here was something else. Encoders always start with a keyframe. – Gyan Mar 24 '19 at 17:03
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To force a keyframe at the 00:00:00.000 time code, you should try using the following flag:

-force_key_frames 00:00:00.000
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  • What does this do exactly? – Warrior Bob Nov 14 '12 at 22:32
  • it will force position the keyframe at 00:00:00.000 time code, which was asked with the original request. – Maxim Nov 14 '12 at 23:58
  • Could you please elaborate: Is this applicable to x264 only, or any codec? What does the time refer to - the output file time? I.e. for overlays, how could I put a keyframe to beginning of any overlayed video? Thanks – Ondra Žižka Mar 23 '19 at 23:13

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