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• What video format will allow Android MediaPlayer.seekTo() to reliably provide frame-accurate scrubbing ?

  8 juillet 2015, par Tim Closs

  We have an iOS app that we are currently rebuilding for Android. The app relies on being able to scrub video with frame accuracy. We have 3D animations that are rendered out as single frames ; we build subsets of frames into lots of small (1-2 second) videos ; and the app provides the ability to scrub those videos and see each individual frame.

  The MP4 videos we initially created work fine on iOS. When we tried to get them working on Android (using the MediaPlayer class), we entered a world of pain ! What we need to do is find a video format that will play and allow frame-accurate scrubbing across all Android devices, using MediaPlayer.seekTo(). Initially we are targetting Android 3.0 and above, but we probably want to stretch back to 2.3.3 after our initial release. Here’s what I’ve discovered so far :

  (A) Android claims that H264 "baseline profile" should be supported everywhere : (URL). However, within that, there are dozens of other settings that may or may not be supported. Is there a more fine-grained list anywhere ? Currently we are converting to H264 within an MP4 container.

  (B) I haven’t yet seen an Android device that will accurately scrub H264 files without inserting keyframes ("intra frames"). iOS will happily take H264 files without keyframes and provide accurate scrubbing. It seems that, to allow accurate scrubbing, we need to insert a keyframe for every frame of the video (the relevant ffmpeg setting is "-g 1"). This significantly increases the file size.

  (C) However, inserting a keyframe for every frame results in a video that will not play at all on the Samsung Galaxy Note 3 (Snapdragon chipset I believe). Reducing the keyframes to every second frame or above seems to work (ffmpeg setting "-g 2").

  To summarise :
  MediaPlayer.seekTo() seems very dependent on the video format, and varies across devices. Is this the intention ? Is there a base level of behaviour that seekTo() is supposed to provide, regardless of format ?

  What video format that will allow frame-accurate scrubbing (using MediaPlayer.seekTo()) across all Android devices (at least for 3.0 and above ?)

• With ffmpeg's image to movie feature, is it possible to pass in frames over a period of time versus all at once ?

  2 novembre 2013, par Zack Yoshyaro

  For the purpose of making a time lapse recording of desktop activity, it is possible so "stream" the frame list to ffmpeg over time, rather than all at once in the beginning.

  Currently, it is a two step process.

  1. save individual snapshots to disc

     im = ImageGrab.grab()
     im.save("frame_%s.jpg" % count, 'jpg')

  2. compile those snapshots with ffmpeg via

     ffmpeg -r 1 -pattern_type glob -i '*.jpg' -c:v libx264 out.mp4

  It would be nice if there were a way to merge the two steps so that I'm not flooding my hard drive with thousands of individual snapshots. Is it possible to do this ?

• Can I use ffmpeg to output jpegs to a memory stream instead of a file

  1er février 2015, par Andrew Simpson

  I have a c# app. I have 100 jpegs (for an example).

  I can easily encode this into a video file.

  When it has finished encoding on the client app I FTP upload to my server.

  It would be ’neater’ if I could not write the video file to a disc but instead write it to a memory stream (or array of bytes) and upload via web service perhaps ?

  I have checked out the ffmpeg documentation but as a c# developer I do not find it natural to understand the c examples.

  I guess my 1st question is it possible and if so can anyone post me an example code in c# ? At the moment I am using the process class in c# to execute ffmpeg.

  I will of course post this code if it would help ?

  Thanks for everyone’s time.