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• jpeg colors worse than png when extracting frames with ffmpeg ?

  5 juillet 2016, par RocketNuts

  When extracting still frames from a video at a specific time mark, like this :

  ffmpeg -i foobar.mp4 -vframes 1 -ss 4:20 -q:v 1 example.png

  I noticed using PNG or JPG results in different colors.
  (Note that the -q:v 1 indicates maximum image quality)

  Here are some examples :

  1. JPG vs PNG
  2. JPG vs PNG
  3. JPG vs PNG

  In general, the JPG shots seem to be slightly darker and less saturated than the PNGs.

  When checking with exiftool or imagemagick’s identify, both images use sRGB color space and no ICC profile.

  Any idea what’s causing this ? Or which of these two would be ’correct’ ?

  I also tried saving screenshots with my video player (MPlayerX), in both JPG and PNG. In that case, the frame dumps in either format look exactly the same, and they look mostly like ffmpeg’s JPG stills.

• FFmpeg : Create a Video Slideshow from PNG Images for MS PowerPoint

  20 septembre 2016, par Klaidonis

  I am using FFmpeg on Windows 7 to create a video from PNG image sequence for Microsoft PowerPoint.

  The best results I have achieved so far, is by using the following command :

  ffmpeg -framerate 10 -start_number 3 -i .\folder\name_%d.png -q:v 0 -c:v libx264 -pix_fmt yuv420p output-video.avi

  It seems perfect, 50 images of total size 30 MB are converted into 200 KB video with no loss in the quality. Placing it in PowerPoint also seems right, but there is a slight color shift (yellow appears darker and possibly more orangish). By using some other conversion options, I obtained a video in PowerPoint where the first image of the video (like album cover art) is exactly as the original but the rest of the video plays with the mentioned color shift.

  When I play this file in VLC, it’s good. Although, if in the settings "Use hardware YUV->RGB conversions" is enabled, colors appear a bit washed out, and white color is a bit gray.

  I also tried to convert the images to a GIF file and at first it seems good but outer edges and numbers from the left and top side are blurred, and the background has turned from white to a bit gray color, although, white segments not on the background are white. The output size is 18 MB. I ended up with a way better GIF 600 KB by converting from the first video file ; just it is slightly more dotted, and the background again is grayish.

  ffmpeg -i output-video.avi output-video.gif

  Could someone help ?

• Slow audio-video sync drift when merging wav and mp4 with ffmpeg

  30 mai 2016, par charlie80

  I have an mp4 file with only a single video stream (no audio) and a wav audio file that I would like to add to the video using ffmpeg. The audio and the video have been recorded simultaneously during a conference, the former from a mixer output on a PC and the latter from a digital videocamera.

  I am using this ffmpeg command :

  ffmpeg -i incontro3.mp4 -itsoffset 18.39 -i audio_mix.wav -c:v copy -c:a aac final-video.mp4

  where I’m using the -itsoffset 18.39 option since I know that 18.39s is the video-audio delay.

  The problem I’m experiencing is that in the output file, while the audio is perfectly in sync with the video at the beginning, it slowly drifts out of sync during the movie.

  The output if ffprobe on the video file is :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'incontro3.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf57.25.100
  
    Duration: 00:47:22.56, start: 0.000000, bitrate: 888 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 886 kb/s, 25 fps, 25 tbr, 12800 tbn (default)
  
      Metadata:
  
        handler_name    : VideoHandler

  and the ffprobe output for the audio file is :

  Input #0, wav, from 'audio_mix.wav':
  
    Metadata:
  
      track           : 5
  
      encoder         : Lavf57.25.100
  
    Duration: 00:46:32.20, bitrate: 1411 kb/s
  
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, 2 channels, s16, 1411 kb/s

  I’m using the latest ffmpeg Zeranoe windows build git-9591ca7 (2016-05-25).

  Thanks in anticipation for any help/ideas !

  ---

  UPDATE 1 : It looks like the problem is upstream the video-audio merging, and could be in the concatenation and conversion of the MTS files generated by the video camera into the mp4 video. I will follow up as I make any progress in understanding...

  ---

  UPDATE 2 : The problem is not in the initial merging of the MTS files generated by the camera. Or, at least, it occurs identically if I merge them with cat or with ffmpeg -f concat

  ---

  UPDATE 3 : Following @Mulvya’s suggestion, I observed that the drift rate is constant (at least as far as I can tell judging by eye). I also tried to superimpose the A/V tracks with another software, and the drift is exactly the same, thereby ruling out ffmpeg as culprit. My (bad) feeling is that the issue could be related to the internal clocks of the digital video camera and the laptop used for audio recording running at slightly different rates (see here the report of an identical issue I just found).