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• Error using FFMPEG to create videos from a list of images

  3 août 2016, par user2308191

  I have a text file that contains the path of some images(the images are in order in the text file), the file looks like this :

  /home/Recording-Session-1456734351095_images/output_0001.png
  
  /home/Recording-Session-1456734351095_images/output_0002.png
  
  /home/annotations/rec_1456734351095/annotated_output_0003.png
  
  .......

  I want to use ffmpeg to create a video from these images. Here is the command I am using :

  ffmpeg -framerate 20 -f image2 -i images.txt -c:v libx264 -r 20 -pix_fmt yuv420p out.mp4

  but it gives me this error :

  [image2 @ 0x32ce7a0] Could not find codec parameters for stream 0 (Video: none, none): unknown codec
  
  Consider increasing the value for the 'analyzeduration' and 'probesize' options

  I tried different numbers for analyzeduration and probesize, but the error still exists, any idea what is the problem ?

• ffmpeg audio and video out of sync when using the raw format

  29 juillet 2016, par Mikhail Novikov

  I have 2 .webm files, one contains video, the other one audio. I need to produce a single mp4 file containing both video and audio, in sync. Here is what i try to do :

  ffmpeg -ss 00:00:00.33 -i user_17624_1-1762.webm -i user_17624_2-1767.webm -r 15 output_good.mp4

  -ss by 0.33s is because video started 0.33s before audio - 1762 and 1767 are frame numbers, so they are 5 frames off, and 15 fps.

  Doing this, i get a perfect recording where video and audio are in sync over the entire file.

  But the thing is, i need to do some alterations of the video frames, and i do it my a C app manipulating the bytes in a raw video stream, so i can’t do it this way, i need to transcode to RAW first, then manipulate, then encode mp4 back from the raw. Removing my C app from the chain to make sure it’s not the problem, it boils down to :

  ffmpeg -ss 00:00:00.33 -i user_17624_1-1762.webm -an -r 15 -f rawvideo -pix_fmt yuv420p -s 1920x1080 ./video.pipe &
  
  ffmpeg -i user_17624_2-1767.webm -vn -ar 44100 -ac 2 -f s16le -acodec pcm_s16le ./audio.pipe &
  
  ffmpeg -an -r 15 -f rawvideo -pix_fmt yuv420p -s 1920x1080 -i ./video.pipe -vn -ar 44100 -ac 2 -f s16le -acodec pcm_s16le -i ./audio.pipe -r 15 output_bad.mp4

  resulting in yes, recording where audio and video are way off from each other, and seems to be also fluctuate over the file duration.

  What am i doing wrong with these video transcodings ? Help me please :)

  Mikhail

• Extract list of specific frames using ffmpeg

  8 juillet 2016, par John Allard

  I’m trying to use ffmpeg on a video to extract a list of specific frames, denoted by their frame numbers. So lets say I want to extract just one frame from ’test_video.mp4’, frame number 150 to be exact. I can use the following command

  ffmpeg -i test_video.mp4 -vf "select=gte(n\, 150)" -vframes 1 ~/test_image.jpg

  But what if I want to exact a list of frames, such as [100, 110, 127, 270, 300] ? I have been looking at this page (https://ffmpeg.org/ffmpeg-filters.html#select_002c-aselect) and can see that there are ways to extract multiple frames based on parity of frame number, timestamps, etc, but I can’t find the syntax for doing what I need to do.

  Ideally I would extract the list of given frames under the naming convention out_image%03d.jpg where the %03d is replaced by the given frame number, although a timestamp would also work.

  Is there a way to do this ?