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• Fix js MediaRecorder video file duration with js or ffmpeg

  20 juillet 2023, par NickG

  I am trying to create a playable video file with js MediaRecorder containing a video and audio stream. So far i managed to record the streams and create video files (.webm as default, .mp4 for Safari due to lacking .webm support).

  


  BUT : The recorded files are missing a duration when inspecting them or when opening them and are therefore not seekable in any videoplayer. For the .webm files i was able to resolve it by simply using this package and fixing the duration : https://github.com/yusitnikov/fix-webm-duration

  


  Unfortunetly, for .mp4 files this doesn't work. Any suggestions how i can fix the .mp4 files to be correctly playable in standard video players ?

  


  Sidenote :
I've also tried to postprocess the .mp4 files with ffmpeg on the server - without success. Weirdly enough, the conversion seems to work correctly on a windows machine, but not on a Unix machine (with the same command used, produces different output). If someone has experience with this, maybe he could guide me in the right direction how i could solve it via postprocessing ?

  


• Enhance text image in x264 encoding

  24 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 scene). 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 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.

• Can I run a program from Command Prompt on only a numbered subset of files ?

  28 août 2020, par Andrew Shibata

  I have an experiment with 2 groups : English speakers and Mandarin-English bilinguals. I have a batch file that works for converting audio files (using ffmpeg) for the English monolingual group. The Mandarin speaker group also has a few additional trials where they record some more sentences in Mandarin and I'd like to either run ffmpeg separately on just those trials or move that subset to a different folder after the fact.

  


  The file formats are [subject ID]-[trial #]-vowels_record.ogg. The English trials are trial #s 6-35 and the Mandarin trials are trial #s 36-50.

  


  The following code WORKS for my English only dataset :

  


  for %%a in ("*vowels_record.ogg") do ffmpeg -i "%%a" "vowel_wavs\%%~na.wav

  


  This is my attempt at figuring out how to get just the relevant files into relevant folders :

  


  for %%a in ("*{6..35}-vowels_record.ogg") do ffmpeg -i "%%a" "vowel_wavs\%%~na.wav"
for %%a in ("*{36..50}-vowels_record.ogg") do ffmpeg -i "%%a" "mandarin_wavs\%%~na.wav"


  


  I have some regex experience, but not as much with making .bat files and I'm unsure what the right way is to target the range of files I'm looking for.