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• ffmpeg adding a lot of time when concatenating files

  27 novembre 2023, par Jovi Juan

  I'm not sure if this will help anyone else, but I was trying to concatenate some files made in Premiere (problem #1) and ffmpeg kept adding time or changing the timeframe, about an hour for a 37 minute file) which was really frustrating.

  


  I essentially was adding a new credit sequence onto the end and wanted to do it without rerendering any of the sourcefiles which in Premiere takes an amazing 8 hours at 4k and often fails or drops audio or video for no apparent reason.

  


  I tried many many things, but what turned out to be the problem was the timescale, which by using ffprobe, turned out to be two subtly different timescales. Arrrgh. Same program (Premiere), same project.

  


  Anyway the probe results were :
codec_name=h264
r_frame_rate=2997/100

  


  And the other
codec_name=h264
r_frame_rate=30000/1001

  


  So I fixed both of them by running it through this script

  


  ffmpeg -i original.mp4 -c copy -video_track_timescale 30000 output.mp4


  


  where original and output were the respective filenames.

  


  When I ran the concatenation script, it worked !
files.txt :

  


  file 'output.mp4'
file 'output2.mp4'


  


  ffmpeg -f concat -i files.txt -c copy concat-movie.mp4


  


  I can only think that Premiere/Adobe is sneakily doing this to files to make such operations in other programs difficult and frustrating. I even made a sequence using the same files and regenerating the credit sequence from there to ensure the timescales and framerates were the same and it still generated files that were different.

  


  Anyway, that was like a day of work. Hope this saves others the same hassle.

  


• Is it possible to merge two or more videos in real-time like this ?

  25 février 2015, par Marko

  Is it possible to play video online that’s made of two or more video files ?

  Since my original post wasn’t clear enough, here’s expanded explanation and question.

  My site is hosted on Linux/Apache/PHP server. I have video files in FLV/F4V format. I can also convert them to other available formats if necessary. All videos have same aspect ratio and other parameters.

  What I want is to build (or use if exist) online video player that plays video composed of multiple video files concatenated together in real-time, i.e. when user clicks to see a video.

  For example, visitor comes to my site and sees video titled "Welcome" available to play. When he/she clicks to play that video, I take video files "Opening.f4v", "Welcome.f4v" and "Ending.f4v" and join/merge/concatenate them one after another to create one continuous video on the fly.

  Resulting video looks like one video, with no visual clues, lags or even smallest observable delay between video parts. Basically what is done is some form of on-the-fly editing or pre-editing, and user sees the result. This resulting video is not saved on the server, it’s just composed and played that way real-time.

  Also, if possible, user shouldn’t be made to wait for this merging to be over before he/she sees resulting video, but to be able to get first part of the video playing immediately, while merging is done simultaneously.

  Is this possible with flash/actionscript, ffmpeg, html5 or some other online technology ? I don’t need explanation how it’s possible, just a nod that it’s possible and some links to further investigate.

  Also, if one option is to use flash, what are alternatives for making this work when site is visited from iphone/ipad ?

• Poor video quality in first few frames using video output options in gganimate

  27 janvier 2021, par Nautica

  I'm trying to export some animations I've made using gganimate through video format as the gifs I'm creating are quite large.

  


  Sample code :

  


  library(gganimate)

p <- ggplot(mtcars, aes(factor(cyl), mpg)) +
  theme_dark() +
  theme(panel.grid = element_line(colour = "white")) +
  geom_boxplot() +
  transition_states(
    gear,
    transition_length = 2,
    state_length = 1
  ) +
  enter_fade() +
  exit_shrink() +
  ease_aes('sine-in-out')

anim_save("example.mp4",
          animate(
            p,
            nframes = 450,
            fps = 25,
            width = 1280,
            height = 720,
            type = "cairo",
            start_pause = 50,
            end_pause = 50,
            renderer = av_renderer()
          ))


  


  Produces the video seen here : https://vimeo.com/505019987

  


  With the standard ggplot2 theme : https://vimeo.com/505020822

  


  This is another example of something I made using gganimate : https://www.youtube.com/watch?v=fHzjl_z_sSo

  


  You can see that the video quality in the first few frames are very bad. In the video with the standard ggplot2 theme and the YouTube video, the gridlines and watermark text are not visible at the start but fade in much later. I don't know much about video codecs but I assume it has something to do with the ffmpeg library the av package/av_renderer() is using. Has anyone experienced something like this ?