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• ffmpeg : Create a fake shadow below alpha channel webm/png sequence

  6 mai 2021, par Beneos Battlemaps

  Purpose : I'd like to render out animated 3D meshes as png sequence to use them as animated tokens for virtual tabletop games. To make the mesh looks more natural I'd like to create a fake show beneath the actual token.

  


  Problem : I have a png sequence 1 (as well as a webm file created with ffmpet out of this png sequence if it makes it easier) with alpha channel. To create the webm I use :
ffmpeg -framerate 24 -f image2 -i Idle_Top.%04d.png -c:v libvpx-vp9 -crf 25 -pix_fmt yuva420p Idle_Top.webm (If its relevant). I'd like to render out the png sequence to a webm file that have the current images as well as the transparent shadow beneath the token combined.

  


  Possible workflow : I think a good way to achieve the wanted shadow effect is to use the alpha channel image as a mask on a black picture with the same resolution as the source image 2. Then you have a complete black version of the image. Then you need to place this image beneath the colored image and make a offset of 10px left and 10px down to create the ilusion of perspective 3. At the end the black image below the colored image must have a transparency as well ( 30% visibility should be enough) 4.

  


  Workflow overview

  


  Assets : I've put the webm file and the png files on my gDrive https://drive.google.com/drive/folders/1wznGaPwhKc2UyPpSZBSISa1gs3oixsHR?usp=sharing

  


  Though I work with ffmpeg on a regular basis I have no clue where to start. Can you please help me out with this interesting problem ?

  


  Best regards
Ben

  


• libavfilter/vf_yadif : Make frame management logic and options shareable

  24 octobre 2018, par Philip Langdale

  libavfilter/vf_yadif : Make frame management logic and options shareable
  I'm writing a cuda implementation of yadif, and while this
  
  obviously has a very different implementation of the actual
  
  filtering, all the frame management is unchanged. To avoid
  
  duplicating that logic, let's make it shareable.
  From the perspective of the existing filter, the only real change
  
  is introducing a function pointer for the filter() function so it
  
  can be specified for the specific filter.
  

  • [DH] libavfilter/Makefile
  • [DH] libavfilter/vf_yadif.c
  • [DH] libavfilter/yadif.h
  • [DH] libavfilter/yadif_common.c

• Video Frame Skipping Issues During Chunking and Uploading in React Native App

  24 février 2024, par Kishore J

  To create a social media platform like Instagram and Facebook, we have incorporated the functionality for users to upload reels-style videos. To enhance the viewing experience, we have implemented a strategy to segment these videos and upload them to the backend.

  


  To achieve this, we have employed the ffmpeg-kit-react-native and rn-fetch-blob libraries to segment videos efficiently. We've written an asynchronous function, chunkVideo, which chunks the input video file into segments of a specified duration. Here's a snippet of the code :

  


  async function chunkVideo(inputVideoFile, fileName, segmentDuration = 3) {
try {
  // Define the cache directory path
  const cacheDir = RNFetchBlob.fs.dirs.CacheDir;
  const outputTSFilePattern = `${cacheDir}/${fileName}_video%d.ts`;
  await FFmpegKit.execute(
   `-i ${inputVideoFile} -codec: copy -start_number 0 -hls_time ${segmentDuration} -hls_list_size 0 -hls_segment_filename ${outputTSFilePattern} -f hls ${cacheDir}/index.m3u8`,
  );
} catch (err) {
  logEvent("chunkVideoError", {error: err?.message});
  errorToast(err, true);
  }
}


  


  While this approach works well for segmenting videos, we encountered an issue where some frames are skipping during the chunking process, leading to a compromised viewing experience for the end-users.

  


  How to mitigate the frame skipping problems ?