Recherche avancée

Sur d’autres sites (6344)

• Extract effective P frame (i.e. real prediction error) with ffmpeg

  23 avril 2017, par Gregoire Mercier

  I would like to extract the P frame from a video to "see" the prediction error.

  When using the following command line :

  ffmpeg -i video.mp4 -vf select='eq(pict_type\,P)' -vsync vfr -q:v 1 p_images_%04d.png 

  It extracts P frames but they are reconstructed as "real" images with a dynamic of [0,255], I would like to have the effective prediction error i.e. before using the related reference image.

  Is that possible ?

  Thanks,
  Greg

• Android mp4 remove rotation and rotate the video stream

  4 mars 2015, par Mathijs Segers

  I’m having some issues trying to remove the rotation value of Android video’s.
  For some reason convertion tools in the cloud cannot seem to handle android’s rotation value correctly. f/e I have a portrait video recorded in 1080x1920 (so the file’s headers tell me it’s actually 1920x1080 with rotation : 90).

  So now I’m trying to convert these video’s to an actual 1080x1920 format when they have this rotation value but i’m kind of stuck, probably using the wrong search terms on SO and Google.

  In the hope of making things clear I’ve actually added some ffmpeg libs to android following these steps, of course with some changes to parameters. I’m building this on a Mac and this all works fine now.
  http://www.roman10.net/how-to-build-ffmpeg-with-ndk-r9/

  Now the following, I have no real clue how these libs work and how to use them or which I actually need or if I even need them at all.

  Is there anyone who can point me in the right direction of solving my issue ? Basicly the video’s are on my android filesystem and I can access them fully, before uploading I want to check the values and remove and rotate the video’s if needed.

• Play video files online sequentially without delay/buffering between videos

  26 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 ?