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• ffmpeg outputs that the first frame of a 25fps video shows for only 1ms

  13 avril 2019, par Chubacca

  I’m using ffmpeg to split up a video by frames. For a video that is 25fps, my expectation would be that it would show frame 0 for 40ms, and then it would show frame 1 for 40ms, etc. However, when I use ffmepg to analyze the video, this is not what I get.

  I pulled frames out of the video using the following commands :

  ffmpeg -i original.mp4 -ss 00:00:00.000 -vframes 1 0.000.png
  
  ffmpeg -i original.mp4 -ss 00:00:00.001 -vframes 1 0.001.png
  
  ffmpeg -i original.mp4 -ss 00:00:00.040 -vframes 1 0.040.png
  
  ffmpeg -i original.mp4 -ss 00:00:00.041 -vframes 1 0.041.png

  In this, I would expect 0.000.png and 0.001.png to be the same frame, but the resulting pngs are different. However, on the flipside, 0.001.png and 0.040.png ARE the same frame, while 0.040.png and 0.041.png are different frames. It seems as though the frame at 0.000.png is only showing for 1ms. I’ve tested this on multiple different videos, with consistent results. Can anybody explain why this is or why my expectations are potentially incorrect ?

  As a side note, when I load the same video into an HTML5 video tag in the browsers, when I play the video the first frame shows for 64 milliseconds, and all other frames show for 40 milliseconds. I can test this by comparing frames for the following commands :

  player.currentTime = 0
  
  player.currentTime = .063 // same frame as 0
  
  player.currentTime = .064 // different frame than .063
  
  player.currentTime = .103 // same frame as .064
  
  player.currentTime = .104 // different frame than .103

  This also defies expectations, and makes matching up frames/times for the video between ffmpeg and html5 video even more annoying. Does anyone know what’s going on here ?

  If it’s helpful, here is the metadata from the video :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'original.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.17.101
  
    Duration: 01:36:16.20, start: 0.000000, bitrate: 2301 kb/s
  
      Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 2200 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 96 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler

• How to convert a single photo into video with some filters ?

  11 avril 2019, par Zedd W

  I have a picture in jpeg format : cat.

  I converted this picture into a video through some ffmpeg filter : scale and zoompan. The video is that the picture is slowly enlarged

  Then, I encountered some problems when using the following command.

  command 1

  ffmpeg -loop 1 -i cat.jpeg -filter_complex "scale=iw*2:-1,zoompan=z='zoom+0.002':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':s=720x960" -pix_fmt yuv420p -vcodec libx264 -preset ultrafast -crf 28 -y -t 5 out.mp4

  command 2 (Just adjust the scale value of command 1)

  ffmpeg -loop 1 -i cat.jpeg -filter_complex "scale=iw*8:-1,zoompan=z='zoom+0.002':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':s=720x960" -pix_fmt yuv420p -vcodec libx264 -preset ultrafast -crf 28 -y -t 5 out.mp4

  Problems :

  1. The picture in the video will zoom in slowly, which is true, but until about the fourth second, the picture will return to the minimum and re-enlarge.Is this the filter parameter I used wrong ?

  2. There is a warning after running the command : [swscaler @ 0x113c66000] Warning: data is not aligned! This can lead to a speed loss. The picture size is 720 x 960 and the video is the same. 720/16 is an integer and 960/16 also an integer. So what not aligned ?

  3. There is another warning : deprecated pixel format used, make sure you did set range correctly. Did I set the pix_fmtparameter wrong ?

  4. command 2 and command 1 are different scale value, But the time they run will vary greatly (If you try to run it). Using a larger scale will have better results. So how to choose a scale value or have better way ?

• How to convert a single photo into video with some filters without losing performance ?

  11 avril 2019, par Zedd W

  I have a picture in jpeg format : cat.

  I converted this picture into a video through some ffmpeg filter : scale and zoompan. The video is that the picture is slowly enlarged

  Then, I encountered some problems when using the following command.

  command 1

  ffmpeg -loop 1 -i cat.jpeg -filter_complex "scale=iw*2:-1,zoompan=z='zoom+0.002':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':s=720x960" -pix_fmt yuv420p -vcodec libx264 -preset ultrafast -crf 28 -y -t 5 out.mp4

  command 2 (Just adjust the scale value of command 1)

  ffmpeg -loop 1 -i cat.jpeg -filter_complex "scale=iw*8:-1,zoompan=z='zoom+0.002':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':s=720x960" -pix_fmt yuv420p -vcodec libx264 -preset ultrafast -crf 28 -y -t 5 out.mp4

  Problems :

  1. The picture in the video will zoom in slowly, which is true, but until about the fourth second, the picture will return to the minimum and re-enlarge.Is this the filter parameter I used wrong ?

  2. There is a warning after running the command : [swscaler @ 0x113c66000] Warning: data is not aligned! This can lead to a speed loss. The picture size is 720 x 960 and the video is the same. 720/16 is an integer and 960/16 also an integer. So what not aligned ?

  3. There is another warning : deprecated pixel format used, make sure you did set range correctly. Did I set the pix_fmtparameter wrong ?

  4. command 2 and command 1 are different scale value, But the time they run will vary greatly (If you try to run it). Using a larger scale will have better results. So how to choose a scale value or have better way ?