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• mp4 video written with ffmpeg has different first frame based on total number of frames

  26 janvier 2023, par Nitzan Weissman

  I'm trying to read and write videos using ffmpeg, and I got an interesting phenomenon where the first frame is not the same in videos I create that are made from the same frames, only with different lengths.

  


  The commands I'm running to reproduce the problem :

  


  ffmpeg -i .mp4 -frames:v 20 -q:v 3 resource_images/00%04d.png

ffmpeg -hide_banner -loglevel error -framerate 30 -y -i resource_images/00%04d.png  -c:v libx264 -pix_fmt yuv420p -frames:v 20 long_video.mp4 -y

ffmpeg -hide_banner -loglevel error -framerate 30 -y -i resource_images/00%04d.png  -c:v libx264 -pix_fmt yuv420p -frames:v 10 short_video.mp4 -y

ffmpeg -i long_video.mp4 -vf "select=eq(n,0)" -q:v 3 long_frame0.png -y

ffmpeg -i short_video.mp4 -vf "select=eq(n,0)" -q:v 3 short_frame0.png -y


  


  The images long_frame0.png and short_frame0.png are different (I loaded them using Python and compared them, there are many differences).

  


  I find it very peculiar, since I create very short videos, it's those videos first frames, and they are keyframes of those videos (I checked it using ffprobe)

  


  What is the cause of this issue and how do I overcome it to create a consistent first frame for a video, regardless of the video length ?

  


• Adding frame numbers to a video, along with total frame duration

  21 novembre 2022, par Abraham Thomas

  I need to add frame numbers to videos along with total frame duration of the video. It should show the first frame and the last frame, along with the current frame.

  


  In this forum someone had posted a command, which gives the current frame number ;
I've used this and this below command works for me :

  


  ffmpeg -i inputvid.mp4 -vf "drawtext=fontfile=Arial.ttf : text='%frame_num' : start_number=1001 : x=(w-tw)/2 : y=h-(2*lh) : fontcolor=white : fontsize=55 : box=1 : boxcolor=black : boxborderw=5" -c:a copy D :\Test\outputvid.mp4

  


  But it doesn't show the total frame duration ;
Is there a way to add to this command ; to show the first frame and last frame of the video as well (I'm on windows) ;

  


• How do I use ffmpeg to extract the total time of a video slice without actually producing the video slice ?

  18 juin 2022, par iChux

  


  I have a video named 'ev.mp4'. Slice the video into segments :

  


  


  # COMMAND 1
ffmpeg -i "ev.mp4" -c copy -map 0 -segment_time 15 -g 9 \
    -sc_threshold 0 -force_key_frames "expr:gte(t,n_forced*9)" \
    -reset_timestamps 1 -f segment ev-%04d.mp4

ev-0000.mp4
ev-0001.mp4
ev-0002.mp4


  


  


  Get each segment time

  


  


  # COMMAND 2
for f in ev-*.mp4;
do
    echo $f == $(ffprobe -v error -show_entries \
    format=duration -of default=noprint_wrappers=1:nokey=1 $f);
done;

ev-0000.mp4 == 17.251000
ev-0001.mp4 == 17.918000
ev-0002.mp4 == 10.444000


  


  


  I am only able to extract the duration of each sliced segment after the videos have existed in a sliced format on the hard drive e.g. ev-0000.mp4

  


  


  My question : is it possible to get the duration of each slice from COMMAND 1 such that instead of producing the sliced files, I will get the duration of each slice ?