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• images->video->web canvas : RGB/YUV issues

  5 février 2016, par nrob

  We’ve written an web app which :

  1. takes 3D, time dependent weather data
  2. tiles each 3D time point to make a 2D frame (written out as a png image)
  3. stitches these frames together into a video (using ffmpeg/avconv)
  4. streams this video into a web app
  5. polls the canvas for frames
  6. sends the frames to the GPU where they are converted back to 3D and ray traced

  You can see the app here, code here and you can see the data video here

  Currently the pngs are written as RGB images, the video codec is in YUV and getting frames from the canvas returns RGB. As such there is a significant loss of information due to the conversion between image spaces.

  Does anyone have suggestions what is the best way round this ?

  I’ve tried a bunch of RGB video codecs, but I can’t get any to work, and I don’t know if the web browser will support it anyway. Can anyone suggest a good RGB codec (both lossy and lossless would be great)

  Also, is it possible to write to YUV images/read them from a video canvas in HTML5 ?

  Ultimately, I don’t even want anything to do with images/videos, I’m just hacking the codecs to stream/compress large animated 3D data volumes

• FFMPEG HLS streaming and transcodding on the fly to HTML player - video duration changes while transcoding

  20 août 2019, par Thomas Tho

  I am trying to make a video streaming server and watch videos directly from web browser. The idea is to make the server to stream video from remote server, transcode with different audio format in local server, and then instantly stream to the client (this is specific way I need it to function).
  This is the FFMPEG code im currently using :

  ffmpeg -i "url" -c:v copy -c:a aac -ac 2 -f hls -hls_time 60 -hls_playlist_type event -hls_flags independent_segments out.m3u8

  The HLS stream is attached to the HTML player with hls.js and it works. However, the video duration is constantly changing while video is being transcoded. I have tried to change video duration with JS like $('video').duration = 120;with no luck.

  How do i make the player to display the video file duration instead of stream current transcoded time ?

  I am also planning to implement video seeking but i am clueless. The current idea is to send seeking time to the server, terminate ffmpeg, and start from specific time. However, i think the player might get stuck on loading and will not start playing without reloading.

• Store a videostream from webcam but as 1s long files that can later be merged together [duplicate]

  17 février 2018, par Jennifer R

  This question is an exact duplicate of :

  • How to segment a video and then concatenate back into original one with ffmpeg
    
    1 answer
    

  I’m trying to store a videostream from a webcam but need it to be 1s long files. I have never worked with storing videofiles so i’m not sure if and how i should use opencv and how those videofiles need to be contained that i can merge them together. I tried the old windows cmd code

  copy /b *.avi combined.avi

  but since avi is sort of a container type i only got as far as the first file. I’m guessing since there’s some container data limiting the first file and i can’t watch it.

  I need help in both questions. How can i store a video stream and how do i merge those videos ? Do i use ffmpeg for the latter and is it possible to edit the container data to the correct length ?