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• FFMPEG : how to pick a random jpeg file from folder

  12 mai 2018, par J. J.

  I run a batch script in expert mode with the program myffvideoconverter.

  My ffmpeg code is : -i example.jpg

  I would like to choose a random jpeg file from the folder automatically instead the file "example.jpg"
  Is it possible ?
  Is it possible to copy the used file into a different folder automatically to make sure that no jpeg will be used two times ? Thank you for your help.

• FFmpeg tee muxer

  14 février 2013, par deed02392

  I'm trying to use the Tee muxer recently introduced to FFmpeg, to both output a stream over UDP and render the output in an SDL window.

  This is because I want to measure latency in my live broadcast system between the input to FFmpeg and its output (i.e. the encoding process latency).

  Can anyone explain how to use it properly ? This is what I have tried :

  ffmpeg -re -i ......\sample_ipod.m4v -f tee "[f=mpegts]udp ://127.0.0.1:1233|[f=sdl]foo"

  I understood this should result in an output stream to UDP and that I could specify additional formats by enclosing like [f=sdl] to mean -f sdl. Then because the sdl muxer requires an argument (the window title) I provided this in the same way the example gives for the stream.

  Hope some FFmpeg expert can shed some light on this. I've even scanned the code that adds the Tee muxer to no avail.

• Do FFMPEG H264 compression presets affect the video quality ? [closed]

  14 novembre 2013, par angainor

  I am definitely not an FFMPEG expert, but according to this document :

  A preset is a collection of options that will provide a certain encoding speed to compression ratio. A slower preset will provide better compression (compression is quality per filesize). General usage is to use the slowest preset that you have patience for. Current presets in descending order of speed are : ultrafast, superfast, veryfast, faster, fast, medium, slow, slower, veryslow, placebo.

  So as I understand it, the ffmpeg presets should not affect the quality of the output video, but should only determine the compression ratio / output file size. Consequently, assuming the same quality setting (I will use -crf 24), the files should be larger for e.g., faster preset than for the slower preset. That would be the only reason to use a slower preset - to get a smaller file size.

  This turns out not to be the case. I encode a HD stream from a handycam using different presets, everything else is the same :

  ffmpeg -y -i "$fname" -vf yadif=1,scale=-1:720 -acodec aac -ab 128k -ac 2 -strict experimental -vcodec libx264 -vpre slow -threads 2 -crf 24 "$outp"

  Surprisingly, I get the smallest file size for veryfast preset ! For example :

  • slower : output bitrate 3500kbps, encoding speed 17 fps, file size 29MB
  • veryfast : output bitrate 3050kbps, encoding speed 34 fps, file size 25MB

  Which I think is not as it should be. Now I wonder, is that due to a worse encoding quality for the veryfast preset ? Or in my case using slower does simply not make sense for some reason ?