Recherche avancée

Sur d’autres sites (6010)

• FFMPEG duplicating the first frame

  13 novembre 2020, par Loïc

  I want to use FFMPEG (the latest version) to cut a 24 fps matroska file. So I am using -ss and -t, but I noticed with VLC that the very first frame is ALWAYS duplicated one time, no matter the file or the duration I choose. While it is not a really serious issue, but I wanted to know if there was a way to prevent that.

  


  Here is the command I am using :

  


  ffmpeg -ss 00:01:26.086 -i file.mkv -t 00:00:02.000 -c:v libx264 -crf 18 output.mp4

  


• Create a rolling X second webcam buffer in Linux, press button saves to file

  13 août 2016, par Grant Gibson

  I’m working on a webcam installation with an ’instant replay’ feature. The concept is basically this :

  1. Webcam captures live, 24/7
  2. When user presses a key, the last (previous) 30 seconds of video saves to a file
  3. I’ll then compress that video using something like FFMPEG and upload to a remote server

  I’m fine with step 3 and beyond, but I haven’t been able to find a solution that does the equivalent of a FIFO buffer for video streams [i.e. pretty much what the ’rewind live tv’ buffer on TiVo does].

  Does anyone know of a way to keep a rolling webcam video/audio buffer that can be exported to a file ?

  Design considerations :

  • I’m planning to use a standard webcam, but open to other suggestions
  • Recording would ideally be 1080p, 30fps
  • Recording must include sound
  • Linux hardware and OS can be specified in the answer, there are no existing pre-requisites. Raspberry Pi would be nice if that’s possible, but equally fine with a small Intel machine (e.g. NUC).
  • There’s no requirement to save the 24/7 stream, but it’s ok if that’s a by-product. So, storage permitting it can be saving to a file continuously for say 12 hours and just ’cat’ the last 30 secs to a separate file, if that’s an option ? But better would be the 30 sec rolling FIFO buffer that could potentially do the whole job in RAM.
  • The ’save instant replay’ button will eventually be a physical pushbutton rather than a keyboard key. However, I’ve got that side of things covered (if the solution is RPi I’d use the GPIO pins, if it’s an Intel box I’d probably use an Arduino in HID mode to simulate a keyboard press).

• SDL2 C++ Capturing Video of Renderer Animation/Sprite

  27 octobre 2016, par alok

  I have an animation/sprite created using SDL2. The animation works fine when it is being rendered to a screen. But now I also want it to be recorded into a video file (locally stored). For this, I am planning on using FFmpeg APIs, to which I’ll be sending a raw RGB pixel data array.

  My problem is with fetching the data from SDL2 APIs.

  What I’ve tried is :

  // From http://stackoverflow.com/questions/30157164/sdl-saving-window-as-bmp
  
  SDL_Surface *sshot = SDL_CreateRGBSurface(0, 750, 750, 32, 0x00ff0000, 0x0000ff00, 0x000000ff, 0xff000000);
  
  SDL_RenderReadPixels(gRenderer, NULL, SDL_PIXELFORMAT_ARGB8888, sshot->pixels, sshot->pitch);
  
  
  
  // From https://wiki.libsdl.org/SDL_RWFromMem
  
  char fName[50];
  
  sprintf(fName, "/tmp/a/ss%03d.bmp", fileCnt);
  
  
  
  
  
  char bitmap[310000];
  
  SDL_RWops *rw = SDL_RWFromMem(bitmap, sizeof(bitmap));
  
  SDL_SaveBMP_RW(sshot, rw, 1); 

  Above does not work. But dumping a single frame into a file with following code works :

  SDL_SaveBMP(sshot, "/tmp/alok1/ss.bmp")

  This obviously is not an acceptable solution - Writing to thousands of BMPs and then using FFmpeg from command-line to create a video.

  What am I doing wrong ? How do you extract data from SDL_RWops ? Is the use of SDL_RWFromMem the right approach to my problem statement ?