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• Ffmpeg mathematical "expression" syntax in filters

  9 novembre 2022, par Jason C

  Multiple ffmpeg filters take a mathematical expression as a parameter, for example setpts and select (examples from docs) :

  


  setpts='1/(25*TB) * (N + 0.05 * sin(N*2*PI/25))';
select=select=between(t\,10\,20)


  


  The docs for each filter are generally good about listing available variables for that specific filter, but the actual syntax of this expression appears (?) to be completely undocumented, despite its heavy use. For example, what functions are available (e.g. sin, between) ? Are boolean combinations allowable and if so, what are the operators ? What other mathematical operators are available ?

  


  What is the syntax of these expressions ? Or, at the very least, is some non-ffmpeg library parsing them and if so, what is it ? That way I can at least look up the syntax. Or have I missed some documentation section somewhere...?

  


• Seek and cut mp4 http stream on the fly with mp4Parser java library

  27 septembre 2016, par xyman

  Is it possible to create new mp4 file(which will be just one small video segment of full length mp4 file) from mp4 http stream without downloading the whole mp4 file to disk and feeding it to mp4Parser. If any other stable java library exist which could do the sam job please point me to it.

  I know it can be done with ffmpeg as explained in this post but i want to avoid using full feature heavy library(cutting the mp4 file doesn’t involve transcoding the video, this operation just repacks the mp4 file) for just cutting the mp4 file.

  ffmpeg -ss 00:01:00.000 -i "http://myfile.mp4" -t 00:02:00.000 -c:a copy -c:v copy output.mp4

• ffmpeg : simple RTMP streaming

  2 avril 2013, par sajad

  I am trying to launch up a rtmp transcoder server using ffmpeg ; that receives udp MPEG-TS streams as input, transcodes it ; and generates an rtmp output to a URL, that can be accessed by users to receive and play the rtmp stream. All these are expected to be performed in a LAN and the output be accessed by all users.

  1) First I don't know where the URL should point to. Is it enought to specify the IP of the system and some optional port ? Is it neccessary that a program should be listening on that port ?

  2) How I can play the stream on the URL ?

  I use a linux ubuntu machine whith IP=10.1.1.229 and I want to transcode multicast stream on this URL : udp://@224.10.1.1:2001.

  here is the command used to transcode input stream and generate rtmp url "rtmp ://10.1.1.229:2020".

  ffmpeg -y -f mpegts -i "udp://@224.10.1.1:2001" -re -vcodec libx264 -maxrate 700k -r 25 -s 640x360 -deinterlace -acodec libfaac -ab 64k -ac 1 -ar 44100 -f flv "rtmp://10.1.1.229:2020"

  and here is the command by which I am trying to play rtmp stream :

  ffplay rtmp://10.1.1.229:2020

  Any guidance would be helpfull. Thank you.