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• Fetching movies' frames via ffmpeg and feed it to vlfeat's sift

  16 novembre 2012, par Karl

  I am going to develop a program that uses ffmpeg and vlfeat on a linux server.

  My task is simply : get some frames from a movie file and feed these frames to vlfeat's sift.

  I am reading through some documents regarding using ffmpeg in c development, mainly here and here. As stated in the site, "There is not much "web based" official documentation for using these libraries." And some tutorials there might be a little outdated. I also read around that the API might differ from version to version. So I would like to ask for the following :

  1. Is it safe to follow this tutorial for the current implementation ?

     • If so, given the impression from above, what are some of the things that should be change for the current implementation ? (currently I got ffmpeg-git-c995644)
     • If not, what are the functions to acquire the frames of the movie file in any format ?

  2. For vlfeat side, if I am to feed a movie's image frame from ffmpeg, what kind of conversion is required so that vlfeat's sift implementation can "digest" the movie's image frame ?

• FFmpeg Centos Compile Error - caused by libwebp (error : implicit declaration of function ‘libwebp_error_to_averror’)

  2 septembre 2022, par fvid1

  I'm trying to compile FFmpeg on Centos 7.9. I followed the official instructions : https://trac.ffmpeg.org/wiki/CompilationGuide/Centos

  


  I need support for WebP images, so I installed libwebp and libwebp-devel via YUM, and used the option --enable-libwebp.

  


  But at the ffmepg "make" stage, the following error is returned :

  


  CC      libavcodec/libwebpenc_common.o
libavcodec/libwebpenc_common.c: In function ‘ff_libwebp_get_frame’:
libavcodec/libwebpenc_common.c:283:17: error: implicit declaration of function ‘libwebp_error_to_averror’ [-Werror=implicit-function-declaration]
                 ret = libwebp_error_to_averror(pic->error_code);
                 ^
cc1: some warnings being treated as errors
make: *** [libavcodec/libwebpenc_common.o] Error 1


  


  Does anyone know why this error is occuring and how it can be corrected ?

  


  I've tried compiling without using --enable-libwebp and it works fine.

  


• Gstreamer video increases latency with decresed FPS

  19 novembre 2024, par Ri Di

  I am using RPI 5 to stream the video :

  


  rpicam-vid -t 0 --camera 0 --nopreview --mode 2304:1296:10:P --codec yuv420 --width 640 --height 360 --framerate 10 --rotation 0 --autofocus-mode manual --inline --listen -o - | ffmpeg -f rawvideo -pix_fmt yuv420p -s:v 640x360 -r 10 -i /dev/stdin -c:v libx264 -preset ultrafast -tune zerolatency -maxrate 300k -bufsize 50k -g 30000 -f mpegts tcp://192.168.0.147:1234


  


  View it with :

  


  gst-launch-1.0 -v tcpserversrc host=0.0.0.0 port=1234 ! queue ! tsdemux ! h264parse ! avdec_h264 ! videorate ! video/x-raw,framerate=10/1 ! videoconvert ! autovideosink sync=false


  


  Problem is that with 10 FPS I get around 2s of latency ! While 56 or 120 FPS results in below 300ms latency.

  


  Is the problem in sender or reader side ? Or both ?

  


  I am not planning to use the 10 FPS, its only for demonstration of problem. But I would like to get lower latency at 56 FPS - just like at 120 FPS (around 80-100 ms difference) or maybe even better, as it seems to get lower with higher FPS.

  


  Maybe there is some kind of buffering parameter which holds frames ?

  


  (of course, when testing with higher FPS I change both numbers in sender and the one in reader command. The camera is v3 RPI official)

  


  Also I'd like to mention that same thing happens with ffplay :

  


  ffplay -i -probesize 3000 tcp://0.0.0.0:1234/?listen