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• Compressing videos from a smartphone

  9 novembre 2016, par fejesjoco

  I have a Nexus 6p with the stock camera. It’s set to record at 1080p, 30fps. Here’s a 5 second sample (11 MB).

  Videos from this phone come out at about 17 Mbps on average. I tried to compress it with ffmpeg with -c:v libx264 -crf 23 -preset veryslow, the result comes out at about 5.5 MB, which is about 9 Mbps.

  I think this bitrate is a bit too much. When I look at torrent file listings, I can see high quality videos at 3 GB in size on average, and if such a movie is 90 minutes long on average, that is about 4-5 Mbps which sounds okay.

  I’m wondering, why the big difference ? I can notice that my video is noisy/grainy (which is expected from a phone), and that might reduce compressibility. I tried a few ffmpeg filters, like hqdn3d and atadenoise, but the noise mostly remained (maybe I didn’t play with it enough). Then I figured, the video is also shaky (which is also expected), and that might reduce compressibility too (and even makes temporal noise filtering less effective). I tried to stabilize it with the deshake filter, but that didn’t help either.

  I know I could just limit the bandwidth to whatever I like, but there must be a reason why ffmpeg thinks it needs a high bandwidth to maintain a certain quality, and a lower bandwidth would just decrease the quality.

  Why do these videos have such a high bitrate ? What’s the best way to compress them more while keeping or even increasing their quality ?

• Use ffmpeg to resize one input's dimension to match another input's dimension

  18 novembre 2022, par Hans GD

  I need to resize one image A to match one dimension of another input B (make height of A match the height of B, for example). I will do this for several pairs of images in a folder, for which I will use a script in the end, but I wanted to know if this particular operation can be done only with ffmpeg.

  


  Again, the final script could read the image, find the size and use scale=-1:height to accomplish the final goal, but is it posible to make the title's operation only with ffmpeg ?

  


• Create 256 color palette video

  2 mars 2020, par rlcabral

  I already have this working by converting the source video to GIF with :

  ffmpeg -y -t 5 source.mp4 -vf fps=10,scale=480:-1,smartblur=ls=-0.5,crop=iw:ih-2:0:0 -hide_banner -loglevel panic output.gif

  And then converting the GIF to MP4, like so :

  ffmpeg -y animated.gif -hide_banner -pix_fmt yuvj420p -loglevel panic -an -loglevel panic final.mp4

  What I want is to convert source.mp4 directly to final.mp4, and have the same 256 color palette as a normal GIF.

  I tried merging both commands together, and although it generates a MP4, the result is a 16 bit video, surprisingly smaller than a 8 bit video.

  Do I need to generate a palette first with palettegen and then re-encode the video with this palette ?