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• Can you "stream" images to ffmpeg to construct a video, instead of saving them to disk ?

  8 juillet 2016, par Brandon

  My work recently involves programmatically making videos. In python, the typical workflow looks something like this :

  import subprocess, Image, ImageDraw
  
  
  
  for i in range(frames_per_second * video_duration_seconds):
  
      img = createFrame(i)
  
      img.save("%07d.png" % i)
  
  
  
  subprocess.call(["ffmpeg","-y","-r",str(frames_per_second),"-i", "%07d.png","-vcodec","mpeg4", "-qscale","5", "-r", str(frames_per_second), "video.avi"])

  This workflow creates an image for each frame in the video and saves it to disk. After all images have been saved, ffmpeg is called to construct a video from all of the images.

  Saving the images to disk (not the creation of the images in memory) consumes the majority of the cycles here, and does not appear to be necessary. Is there some way to perform the same function, but without saving the images to disk ? So, ffmpeg would be called and the images would be constructed and fed to ffmpeg immediately after being constructed.

• Android : mp4 file plays when downloaded but when choosing "Video" player gets "Cannot play video"

  14 janvier 2014, par gview

  I've converted the video to an mp4 with ffmpeg using the h264 codec and AAC, and used the baseline profile.

  Videos are 540x360x250kbps

  I then ran qt-faststart on the file to move the atoms into the right order.

  I've stuck the file up on a wiki we use and created a link to it.

  My test phone is a Samsung Galaxy S3.

  When I browse to the page that has links to the mp4's on it, and I click on them, I get a popup window with 2 options : Internet and Video.

  If I download the videos using the "Internet" option, I can play them on the phone without issue.

  I've done other encodings with the main profile as well, and these also play fine. I thought that a powerful phone like the s3 would be able to handle the more advanced compression schemes available in h264, however I've also browsed the Android docs in regards to supported video formats, and it seems to state that only the "baseline" compression profile is supported.

  Regardless, what doesn't work is trying to use the "Video" option which I assume tries to stream the video.

  For the wiki in question, clicking on the link reveals that the content-type and content-length headers are being set :

  Content-Length  6175996
  
  Content-Type    video/mp4;charset=UTF-8

  Clicking on the link with a browser invokes a player (Quicktime in most cases) that can play the mp4's.

  Is there more to having the file HTTP streamable beyond making a link to it ? Why won't my Android 4 play these files ?

  UPDATE :
  I decided to make a quick HTML5 page using the video tag, and the videos do play on both my Galaxy S3 and the latest IOS.

• Revision bf0570a7e6 : Merge "optimize 8x8 fdct rounding for accuracy" into experimental

  23 février 2013, par Yaowu Xu

  Merge "optimize 8x8 fdct rounding for accuracy" into experimental