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• Concatenate chunk containg headers to another chunk in h264

  18 novembre 2014, par Ortixx

  I’m trying to extract thumbnails from a torrent stream by downloading the first couple of chunks to get the headers, another set of chunks from the middle and then concat them to have a single video file.

  For this I’m using nodejs but I’m having trouble with the concatenation part. Obviously the headers include the length of the video so if I simply concat another chunk to the end of the headers chunk, it won’t work.

  In other words, I have 2 chunks of a video file : The first one contains the headers and some material and the other one is fully composed of a video stream. I want to combine the two to form a single video file
  So my question is how can I make this work properly if at all ?

• Is there a way to eliminate seek time when decoding part of a video using ffmpeg ?

  17 décembre 2019, par Babis

  I’ve got some MKV videos encoded with FFV1. For each of the frames, I want to run some complex and time-intensive python or matlab code, so I’m using multithreading, where each thread works on an individual image.

  I’ve tried extracting a single frame from the video using -ss, but it’s terribly inefficient.

  The most efficient way is to decompress everything into images in one go, but then I’m writing to disk, and then I’ll be reading from disk, therefore it’s not ideal either.

  I’ve tried using a ram disk to export images to, and reading them from python/matlab, but it’s not great performance-wise either. Also, I have to split the export into several batches, as the video file is 20GB and all of the exported images will not fit into memory

  Is there a way to rapidly extract individual frames from ffmpeg directly into RAM (or ram disk), so that they can be used by another program ? For example using something like a lookup-table.

  For reference, each video is about 20GB, comprised of 50000 frames, and they are all keyframes (it’s for archival purposes)

• Parsing An ArrayList of BufferedImages From FFmpeg

  4 juin 2015, par user3725743

  I am using FFmpeg in my java app to turn a video into an ArayList of BufferedImages. Im am using this code to split a video file into individual jpg frames :

  builder.command(FFmpeg, "-i", "<video url="url">", "-vf", "fps=5,scale=128:128,format=rgb8,format=rgb24", "out%d.jpg");
  
  </video>

  This produces a folder full of jpg frames, it works fine. But I would rather not write them to individual files, I would rather make that output turned into an ArrayList of BufferedImages, WITHOUT having to write each frame to a seperate file.

  This should be what the command line would look like for the above code :

  FFmpeg.exe -i <video url="url"> -vf fps=5,scale=128:128,format=rgb8,format=rgb24 out%d.jpg
  
  </video>

  If its not possible to parse the ArrayList directly, what other solutions do I have which would be more elegant ?