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• Modifying incorrect h.264 dimension in existing video file

  11 juin 2015, par RichyJ

  After searching a lot, I’m more confused than ever !! To summarise :

  I recorded a video using my HTC One M8, using 1920x1088 resolution, and it came out fine. The next day, for some reason, in the settings I changed to 1920x1080 and the next video was weird - green bar across the top, diagonal green lines throughout and odd colour stripes. The underlying image was fine, although there seem to be some ’frame jumps’ at times. Unfortunately, this second video contained a section I would like to keep, so I’m trying to fix it...

  I’ve learned a bit about AVC/H.264, but it’s pretty confusing. Essentially, I wonder whether I can just change the ’1080’ in the file info to ’1088’ and salvage the footage - there’s no audio to worry about. I read that since 1080 is not directly divisible by 16, most encoders actually do 1088 then the player discards the remaining 8 lines at playback time. I wonder whether this is the root of the problem ? I tried to get into NALs, SPS/PPS etc, but couldn’t really fathom whether this was even relevant to my problem. A hex search didn’t even find anything that looked like the NALs given as examples elsewhere :

  Finding SPS/PPS data strings

  What does this NAL header data mean ?

  Fetching dimensions of a video

  I’ve loaded both files into a Hex editor and compared as best I can (around the moov and avcC parts), but haven’t fixed it yet. One of the single byte changes I made and saved to a new ’test’ file brought up additional info in the mediainfo program, showing that the original recording was at 1088 - this hadn’t been there before, but it still played wrongly. I found info regarding the encoding of height and width (units-1 * 16) but couldn’t work out how to use this info in practice.

  I tried ffmpeg and dumping to raw video, but couldn’t make this play at all as a yuv file.

  So, my question is, will I be able to change just one byte (or a few) in the file, to make it read as 1088 to the player, or am I looking in totally the wrong direction ?!? Is this even possible ? As I say, the actual images look intact throughout, just the colours are wrong and the lines are there, so I believe it’s something to do with YCrCb problems, but at this point, I’m lost...

  I know this isn’t specifically about programming, but the above links were all from this site, so thought it might be OK to ask here. Any help would be much appreciated !!

  I’ve recreated the conditions and done 2 short clips at 1080 and 1088 for you to see the problem but as I’m new, I can’t post them here yet. They’re on my Photobucket page if you are willing to look at them (hope this isn’t breaking the rules !!). The blueish line at the bottom is the windowsill...

  1088 still

  1080 still

• Hung out to dry

  31 mai 2013, par Mans — Law and liberty

  Outrage was the general reaction when Google recently announced their dropping of XMPP server-to-server federation from Hangouts, as the search giant’s revamped instant messaging platform is henceforth to be known. This outrage is, however, largely unjustified ; Google’s decision is merely a rational response to issues of a more fundamental nature. … Continue reading →

• Real-time streaming of rawdata images to Android with FFMPEG

  29 juillet 2015, par Philies

  CONDITIONS

  I have an C++ server (Linux) and want to transmit rawdata images (RGB, 32bit) to an Android device in real-time.
  The server generates the rawdata images (with or without bitmap header) continuously every x miliseconds. Now, I want to put the rawdata images into a stream and transmit them without much delay to the Android client.

  I’ve chosen FFMPEG for this kind of job.

  The input for FFMPEG should be the rawdata images, which are generated just in time. The output should be an rtsp stream (h264 or is another format better ?).
  On client side I will play the stream with the Android MediaPlayer. That works for a RTSP url like rtsp ://184.72.239.149/vod/mp4:BigBuckBunny_115k.mov

  ---

  PREVIOUS APPROCH :

  I’ve installed FFMPEG on my server.

  Depending on this question : https://ffmpeg.org/pipermail/ffmpeg-user/2013-April/014617.html ... here is my FFMEG command :

  ffmpeg -an -f rawvideo -vcodec rawvideo -pix_fmt rgb32 -r 10 -i -vcodec libx264 -r 30 -tune zerolatency -preset ultrafast -bsf:v h264_mp4toannexb -f mpegts udp://192.168.1.20:1234

  Explanation of the parameters :

  • -an = ignore audio
  • -report = log file in current directory

  INPUT :

  • -f = rawvideo (video format)
  • -vcodec = rawvideo (video codec)
  • -pix_fmt = rgb32
  • -r = 10 (frame rate)

  OUTPUT :

  • -vcodec = libx264
  • -r = 30 (frame rate)
  • -bsf:v = h264_mp4toannexb
  • -f = mpegts udp ://192.168.1.20:1234

  ---

  C++ Server Code Snippet :

  /* -------  Get image rawdata from source ------- */
  
  ...
  
  /* -------  Create image header which fits to the image rawdata ------- */
  
  ...
  
  
  
  /* ------- Store the picture local (not necessary?) ------- */
  
  FILE *f;
  
  f = fopen("/home/philies/test.bmp","wb");
  
  
  
  //Write Bitmap Headers
  
  fwrite(&imageFileHeader,1,sizeof(imageFileHeader),f);
  
  fwrite(imageInfoHeader,1, imageInfoHeader,f);
  
  
  
  //Write Bitmap Rawdata
  
  fwrite(lastImage.GetBitmapRawData(),1,imageSize,f);
  
  
  
  
  
  —> ffmpeg ???

  ---

  PROBLEMS/QUESTIONS :

  1. How can I specify the rawvideo of the ffmpeg command respectively how can I specify my bitmap rawdata (with or without header ?) as the input of the FFMPEG ?

  2. Is the FFMPEG command correct ?

  If I fire the FFMPEG command in the terminal I get this error :

  vcodec : no such file or directory

  EDIT :
  In the first step, I will open the udp stream with the VLC player on my Android device. After that I will set up a FFserver to create a RTSP stream