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• Positioning an overlay produces a different outcome to drawtext with ffmpeg

  2 février 2021, par Alex Gurr

  I have an image overlay I'm positioning using the equation : overlay=1015:(((H-h)/2) + 225 + 60) which works as expected.

  


  However, when I try and apply this to drawtext x=1045:y=(((H-h)/2) + 225 + 60) it doesn't position at the same y coordinate ?

  


  Are there any nuances people know about ?

  


  Thanks.

  


• Change keyframe interval losslessly to produce mpeg-dash content

  25 mars 2023, par Eeel

  I have a case where i have a mkv file encoded to a 2.5 GB file with x264/CRF settings, in this file group of pictures are not of equal duration (i.e 2,4 or 6 seconds ...).

  


  Now i want to create a mpeg-dash version of the file by extracting the video track to mp4 and set the keyframe interval to 2sec losslessly preserving size (minus other audio and subtitle tracks)

  


  What i already have that work :

  


  Fix keyframe to 2s with x264 :

  


  -codec:v libx264 -force_key_frames 'expr:gte(t,n_forced*2)' -movflags faststart


  


  But it require also encoding settings that change the quality :

  


  -b:v 3500k -maxrate 6000k -bufsize 3500k


  


  In this case i don't need to change the quality from CRF encoding, just change keyframe interval and set faststart flag.

  


  note :
I have detailed bitrate informations about the file obtained by parsing output of ffprobe : average, min and max bitrate in kb/s.
Please avoid solution using -crf 0, mpeg-dash files are later crypted using MP4Box that crash with CRF encoded files.

  


  How can i do this using ffmpeg ?

  


  Edit :

  


  Sorry my question is not clear, i'm fine with re-encode, i want to preserve quality as much as possible.

  


  Using a little more than source mean bitrate for the -b:v parameter the resulting file size is almost same as source, metric test results are not as good i expect :

  


  PSNR 41.03 (expected 44+)
VMAF 76.32 (expected 92+)


  


  Is my bitrate approch good ? Is there anything i can try to improve metric results ?

  


• How to setup a video chunker or FFMPEG to bypass Cloudflare ?

  20 avril 2021, par RustyGates

  In full transparency, I am a noob so please forgive my lack of appropriate lingo as I am just barely starting to learn the languages of web development. Hope you don't have to try and decipher too much of what I'm trying to say.

  


  So in an attempt to put this as simply as possible.

  


  I have a PHP Script CMS that I have been doing some extensive custom work to. As mentioned, I am still learning for the most part and while my front end skills are getting very well polished, I'm still completely lose mostly when it comes to back end endeavors. And for reference, the CMS I am using is Wowonder from Codecanyon. It's essentially just a social media cms, like Facebook.

  


  I have this installed on my own dedicated server, have WHM/Cpanel, all that good stuff. I also have my website/domain setup through Cloudflare properly. This is where the issue arises. Cloudflare limits uploads to 100 megabytes. Some of the users on my website will be uploading videos and media much bigger than 100 megabytes. (Up to 10 gigabytes in some cases). I have researched the issue long and hard and it would seem to me the obvious was to resolve the problem would be to use a video chunker (and/or something like FFMPEG ? But not sure if FFMPEG Is capable of it. Am just assuming).

  


  I understand the basic, general idea of what chunkers do and have found some seemingly good options. Will post a couple below just as an example but not necessarily options I was considering.

  


  [https://github.com/blueimp/jQuery-File-Upload][1]

  


  [https://github.com/c0decracker/video-splitter][2]

  


  [https://github.com/appijumbo/video-chunk][3]

  


  So again, I understand the basic idea, it would chunk up the video while uploading (somewhere beneath the 100 megabyte maximum) to bypass Cloudflare's limit, and then stitch the video back together so it's in it's in it's complete form again. However, with a website that has many users uploading, I have not the slightest idea what the best solution is, or if this is the best solution at all, and if it is, how to implement it properly.

  


  I have also installed FFMPEG on my server and did so successfully but not sure how to implement that properly either now how to tell it that it should automatically encode any videos uploaded to the website by any users and so on, nor sure if it's possible to do chunking with it although it seemingly is ?

  


  Any advice is on the topic is much appreciated and I would be much obliged. Thanks in advance.