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• DXGI Desktop Duplication : encoding frames to send them over the network

  13 novembre 2016, par prazuber

  I’m trying to write an app which will capture a video stream of the screen and send it to a remote client. I’ve found out that the best way to capture a screen on Windows is to use DXGI Desktop Duplication API (available since Windows 8). Microsoft provides a neat sample which streams duplicated frames to screen. Now, I’ve been wondering what is the easiest, but still relatively fast way to encode those frames and send them over the network.

  The frames come from AcquireNextFrame with a surface that contains the desktop bitmap and metadata which contains dirty and move regions that were updated. From here, I have a couple of options :

  1. Extract a bitmap from a DirectX surface and then use an external library like ffmpeg to encode series of bitmaps to H.264 and send it over RTSP. While straightforward, I fear that this method will be too slow as it isn’t taking advantage of any native Windows methods. Converting D3D texture to a ffmpeg-compatible bitmap seems like unnecessary work.
  2. From this answer : convert D3D texture to IMFSample and use MediaFoundation’s SinkWriter to encode the frame. I found this tutorial of video encoding, but I haven’t yet found a way to immediately get the encoded frame and send it instead of dumping all of them to a video file.

  Since I haven’t done anything like this before, I’m asking if I’m moving in the right direction. In the end, I want to have a simple, preferably low latency desktop capture video stream, which I can view from a remote device.

  Also, I’m wondering if I can make use of dirty and move regions provided by Desktop Duplication. Instead of encoding the frame, I can send them over the network and do the processing on the client side, but this means that my client has to have DirectX 11.1 or higher available, which is impossible if I would want to stream to a mobile platform.

• Frame Accurate Seeking in WebM

  11 janvier 2016, par SapphireSun

  I’m trying to do a somewhat tricky thing with WebM. I am trying to encode a stack of 256 biological images as a WebM. The time dimension of motion is very similar to the space dimension of the image stack so the compression ratios are insanely good. However, I am having trouble decoding the movie frames. I know that WebM uses an IPB predictive coding scheme, but I was reading several blog posts and discussion groups from WHATWG from 2011, and they said that frame accurate seeking was working in Chrome at that time.

  When I do video.currentTime = 0, I correctly get this :

  

  However, if I do video.currentTime = 0.34 (for example) I get something that looks like this :

  

  It looks like I’m getting a random poorly predicted frame. Am I just encoding the video wrong ? When I play it normally it looks fine.

  I encoded the video using 256 pngs using ffmpeg compiled with libvpx using the VP8 codec.

  ffmpeg -y -framerate 60 -start_number 0 -pattern_type glob -i '*.png' -qmin 10 -qmax 42 out.webm

  References to the WHATWG and some other info from 2011 :

  WHATWG discusses frame accuracy :

  https://lists.w3.org/Archives/Public/public-whatwg-archive/2011Jan/0372.html

  BBC Tech Director talking about frame accuracy :

  http://www.bbc.co.uk/blogs/bbcinternet/2011/02/frame_accurate_video_in_html5.html

• Combine 2 .FLV videos

  4 décembre 2015, par Rune

  For the last 4 hours I’ve been trying to combine 2 .flv files into one using ffmpeg (or well, just C# in general).

  Here’s what I got so far :
  I’ve converted both the videos to .mp4 videos :

  "-i " + videoFileLocation + " -c copy -copyts " + newConvertedFileLocation

  I have then combined the two .mp4 files into a single one using :
  (txtPath is the text file with the two mp4 file locations)

  "-f concat -i " + txtPath + " -c copy " + saveLocation

  This ends up with an mp4 file which contains the combination of both the videos BUT with the following fault :

  The length of the first video is 0:05

  The length of the second video is 6:11

  However the length of the combined video is for some reason 07:51 - thus the video runs at a slower pace than it should.

  Furthermore the audio is async with the video.

  What am I doing wrong here ?

  I haven’t used ffmpeg before and I just wanna get this working.

  Any help is greatly appreciated !

  As requested here is the output from running ’ffmpeg -i input1.flv -i input2.flv’ :

  ffmpeg version 2.7 Copyright (c) 2000-2015 the FFmpeg developers   built with gcc 4.9.2 (GCC)...
  
  
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'filepath\input1.flv':   Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      creation_time   : 1970-01-01 00:00:00
  
      encoder         : Lavf53.24.2   Duration: 00:00:05.31, start: 0.000000, bitrate: 1589 kb/s
  
      Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1205 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 384 kb/s (default)
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
        handler_name    : SoundHandler Input #1, flv, from 'filepath\input2.flv':   Metadata:
  
      audiosize       : 4476626
  
      canSeekToEnd    : true
  
      datasize        : 23876671
  
      videosize       : 19004263
  
      hasAudio        : true
  
      hasCuePoints    : false
  
      hasKeyframes    : true
  
      hasMetadata     : true
  
      hasVideo        : true
  
      lasttimestamp   : 372
  
      metadatacreator : flvtool++ (Facebook, Motion project, dweatherford)
  
      totalframes     : 9298
  
      encoder         : Lavf56.36.100   Duration: 00:06:11.92, start: 0.080000, bitrate: 513 kb/s
  
      Stream #1:0: Video: h264 (High), yuv420p, 646x364 [SAR 1:1 DAR 323:182], 400 kb/s, 25 fps, 25 tbr, 1k tbn, 50 tbc
  
      Stream #1:1: Audio: aac (LC), 44100 Hz, stereo, fltp, 96 kb/s At least one output file must be specified