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• Enhance text image in x264encoding

  23 août 2016, par useprxf

  I’m making use of x264 for remote desktop streaming. The goal is to achieve both low bitrate and high video quality within the computation budget. The current parameter set I used almost achieve this goal, but it fails in handling images with many texts (e.g. browsing websites schene). The text in image is blurred and affects the user experience.

  I think it’s the quantization in x264 that causes this. The quantization after DCT transform will eliminate high frequency sinals which mainly correspond to texts in image.

  So, my question is how to do improve the text quality in x264 encoding ?

  My idea : when the bitrate stays at a low level for a period of time,

  1. set crf to be 0 (lossless) ;
  2. encode current frame as an IDR frame and then send it ;
  3. recover the crf.

  Also, a flag should be used to prevent resending when bitrate keeps low for a long time. I haven’t try this method since I don’t know how to mark a frame as an IDR frame manully and then encode it.

• Syncronize keytimes of audio and video by adding automatic pauses

  2 février 2020, par Alexander Rodríguez

  I would to ask for help regarding this matter. I am a beginner in the use of FMMPEG and I want to know if it is possible to perform the algorithm to edit a video file with an audio file.

  Let’s suppose that you have an Audio and Video clips.
  The Audio has a keytimes on 0s, 5s and 11s and the Video has a keytimes on 0s, 3s, and 16s. This keytimes are in the following TXT file :

  Audio   Video
  
  0s      0s        Audio and video playback starts.
  
  5s      3s        (1)
  
  11s     16s       (2)

  The algorithm takes in the input an Audio clip, Video clip and the TXT file, I want (automaticaly) compute pauses and sync clips according to the following explanation :

  (1) During the first 5 seconds of audio, the first 3 seconds of video are played. Since the video lasts less than the audio, a 2 second pause should be inserted after the 3rd second of video (to match the 5 second video’s length).

  (2) From the second 5 to second 11 the audio is played, from second 3 to 16 the video will be played at the same time. Since the audio´s length will be 6 seconds and the video’s length will be 13 seconds, a 7 second pause should be added to the video.

  I have read and searched a lot about this, but I haven’t found anything that helps me to start this algorithm. Could you help me, please ?

  I apologize in advance if it is a duplicated ask.

• "Transcode" copying video/audio codec

  22 septembre 2012, par JunCTionS

  I took some very shaky video, and went online to try and find how to stabilize it. I came upon this nice blog that uses transcode for it.
  Following the blog instructions it worked very nice, but the end result had a lot of compression artifacts. This I imagine is mostly due to using xvid as a new codec.

  My intention is reuse the codec the camera originally used which is H.264/AVC but I haven't found a way of doing so (ran into various dead ends using either encoder -y mov... or -y ffpmeg.

  In particular when using -y ffmpeg -F "-vcodec copy -acodec copy" it prints out :

  [export_ffmpeg.so] warning: Video template standard must be one of pal/ntsc

  but running

  ffmpeg -i input.mov -vcodec copy -acodec copy output.mov

  Presents no problem.

  Any idea on how to do this ? or an alternative to stabilize video on linux ?.