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• Synchronizing screencasting (ffmpeg) and capturing from the webcam (OpenCV)

  24 avril 2013, par lyuba

  As from my previous questions, I am trying to build a simple eye tracker. Decided to start from a Linux version (run Ubuntu).

  To complete this task one should organize screencasting and webcam capturing in such way that frames from both streams exactly match each other and there is the same number of frames in each of them totally.

  Screencasting fps fully depends on the camera's fps, so each time we get the image from the webcam we can potentially grab a screen frame and stay happy. However, all the tools for the fast screencasting, like ffmpeg, for example, return the .avi file as the result and require the fps already known to be started.

  From the other side, tools like Java+Robot or ImageMagick seem to require around 20ms to return the .jpg screenshot, which is pretty slow for the task. But they may be requested right after each time the webcam frame is grabbed and provide the needed synchronization.

  So the sub-questions are :

  1. Does the USD camera's frame rate vary during a single session ?
  2. Are there any tools which provide fast screencasting frame by frame ?
  3. Is there any way to make ffmpeg push a new frame to the .avi file only when program initiates this request ?

  For my task I may either use C++ or Java.

  I am, actually, an interface designer, not the driver programmer, and this task seems to be pretty low-level. I would be grateful for any suggestion and tip !

• Problem compiling libsrt for ffmpeg, library not found using pkg-config

  3 juin 2022, par Kodsama

  I am trying to build ffmpeg and dependencies from sources (as it will be used from a container on aws) but I have hard time with ffmpeg and pkg-config.

  


  I compile static libraries, among which libsrt from sources and put generated files to well defined directories. pkg-config finds srt without problem but ffmpeg doesn't for some reason (see output below).

  


  Here is how it looks like :

  


  Build code (I extracted the interesting parts, other libraries are built as well, I added prints to be able to see what happens) :

  


  echo "*** Building libsrt ***"
cd $BUILD_DIR/srt*
make distclean
PKG_CONFIG_PATH="$TARGET_DIR/lib/pkgconfig" \
  PATH="$BIN_DIR:$PATH" \
    cmake -G "Unix Makefiles" \
    -DCMAKE_INSTALL_PREFIX="$TARGET_DIR" \
    -DCMAKE_INSTALL_LIBDIR="$TARGET_DIR/lib" \
    -DCMAKE_INSTALL_INCLUDEDIR="$TARGET_DIR/include" \
    -DCMAKE_INSTALL_BINDIR="$BIN_DIR" \
    -DENABLE_SHARED:bool=off \
    -DENABLE_C_DEPS:bool=on \
    -DENABLE_STATIC:bool=on
make -j $jval
make install
echo '========================================================================'
pwd
echo "$TARGET_DIR"
echo "$BUILD_DIR"
echo 'target_dir=' && ls "$TARGET_DIR"
echo 'lib=' && ls "$TARGET_DIR/lib"
echo 'lib/pkgconfig=' && ls "$TARGET_DIR/lib/pkgconfig"
echo 'bin_dir=' && ls "$BIN_DIR"
echo 'include=' && ls "$TARGET_DIR/include"
echo 'path=' && echo $PATH
pkg-config --modversion srt
export PKG_CONFIG_PATH="$TARGET_DIR/lib/pkgconfig":$PKG_CONFIG_PATH


echo "*** Building FFmpeg ***"
cd $BUILD_DIR/FFmpeg*
make distclean
PATH="$BIN_DIR:$PATH" \
  ./configure \
    --prefix="$TARGET_DIR" \
    --pkg-config-flags="--static" \
    --extra-cflags="-I$TARGET_DIR/include -I$TARGET_DIR/usr/local/include -I/usr/local/cuda/include" \
    --extra-ldflags="-L$TARGET_DIR/lib -L$TARGET_DIR/usr/local/lib -L/usr/local/cuda/lib64" \
    --extra-libs="-Wl,-Bstatic -lharfbuzz -lfreetype -lpng -lz -lbz2 -Wl,-Bdynamic -lm -ldl -lpthread -lsrt -lssl -lcrypto" \
    --extra-ldexeflags="-Wl,-Bstatic" \
    --nvccflags="-gencode arch=compute_75,code=sm_75 -O2" \
    --bindir="$BIN_DIR" \
    --enable-pic \
    --enable-ffplay \
    --enable-fontconfig \
    --enable-frei0r \
    --enable-gpl \
    --enable-version3 \
    --enable-libass \
    --enable-libfribidi \
    --enable-libfdk-aac \
    --enable-libfreetype \
    --enable-libmp3lame \
    --enable-libopenjpeg \
    --enable-libopus \
    --enable-libsoxr \
    --enable-libspeex \
    --enable-libtheora \
    --enable-libvidstab \
    --enable-libvorbis \
    --enable-libvpx \
    --enable-libwebp \
    --enable-libx264 \
    --enable-libx265 \
    --enable-libxvid \
    --enable-libzimg \
    --enable-nonfree \
    --enable-openssl \
    --enable-cuda-nvcc \
    --enable-cuvid \
    --enable-nvenc \
    --enable-libsrt \
    --enable-libnpp || tail -n 100 ${HOME}/build/FFmpeg*/ffbuild/config.log

PATH="$BIN_DIR:$PATH" make -j $jval
make install


  


  This what I get printed in the logs (I put [...] to take away parts which are not relevant) :

  


  [...]
[100%] Built target srt-file-transmit
Install the project...
-- Install configuration: "Release"
-- Installing: /codebuild/output/ffmpeg/target/lib/libsrt.a
-- Installing: /codebuild/output/ffmpeg/target/include/srt/version.h
-- Installing: /codebuild/output/ffmpeg/target/include/srt/srt.h
-- Installing: /codebuild/output/ffmpeg/target/include/srt/logging_api.h
-- Installing: /codebuild/output/ffmpeg/target/include/srt/access_control.h
-- Installing: /codebuild/output/ffmpeg/target/include/srt/platform_sys.h
-- Installing: /codebuild/output/ffmpeg/target/include/srt/udt.h
-- Installing: /codebuild/output/ffmpeg/target/lib/pkgconfig/haisrt.pc
-- Installing: /codebuild/output/ffmpeg/target/lib/pkgconfig/srt.pc
-- Installing: /codebuild/output/ffmpeg/bin/srt-live-transmit
-- Up-to-date: /codebuild/output/ffmpeg/bin/srt-live-transmit
-- Installing: /codebuild/output/ffmpeg/bin/srt-file-transmit
-- Up-to-date: /codebuild/output/ffmpeg/bin/srt-file-transmit
-- Installing: /codebuild/output/ffmpeg/bin/srt-tunnel
-- Up-to-date: /codebuild/output/ffmpeg/bin/srt-tunnel
-- Installing: /codebuild/output/ffmpeg/bin/srt-ffplay
========================================================================
/codebuild/output/ffmpeg
/codebuild/output/ffmpeg/target
/codebuild/output/ffmpeg/build

target_dir=
bin
etc
include
lib
share
ssl
var

lib=
cmake
[...]
libsrt.a
libssl.a
[...]
pkgconfig

lib/pkgconfig=
[...]
haisrt.pc
[...]
libcrypto.pc
libssl.pc
[...]
openssl.pc
[...]
srt.pc
[...]

bin_dir=
[...]
srt-ffplay
srt-file-transmit
srt-live-transmit
srt-tunnel
[...]

include=
[...]
srt
[...]

path=
/root/.cargo/bin:/root/miniconda3/bin:/usr/local/cuda/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/codebuild/user/bin
1.4.3
========================================================================
*** Building FFmpeg ***
ERROR: srt >= 1.3.0 not found using pkg-config

If you think configure made a mistake, make sure you are using the latest
version from Git.  If the latest version fails, report the problem to the
ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.freenode.net.
Include the log file "ffbuild/config.log" produced by configure as this will help
solve the problem.
tail: cannot open '/root/build/FFmpeg*/ffbuild/config.log' for reading: No such file or directory

[Container] 2021/06/09 15:03:22 Command did not exit successfully ./build.sh exit status 1
[Container] 2021/06/09 15:03:22 Phase complete: BUILD State: FAILED
[Container] 2021/06/09 15:03:22 Phase context status code: COMMAND_EXECUTION_ERROR Message: Error while executing command: ./build.sh. Reason: exit status 1


  


  Any idea what can be wrong ?

  


  Thanks !

  


• ffmpeg record timelapse camera v4l2

  21 mars 2019, par Paul G.

  How can I instruct ffmpeg (v. : 3.4.5) to record only one frame per minute from my video camera at /dev/video0 and copy it to a new file with 30 frames per second ? Goal is timelapse video of some months and record only one frame per minute into the out video to save space and processing power instead of just capturing the camera at 30fps and then preprocess the huge video file for speed up...

  The camera delivers a 1920x1080 30fps stream with "mjpeg" selected in commandline. I would like to keep the raw frames and just copy them into the out file. I tried this command to get 1fps input to 30fps output but this seems not to work :

  ffmpeg -framerate 1 -input_format mjpeg -i /dev/video0 -r 30 -c:v copy -an out.mp4
  
  
  
  [video4linux2,v4l2 @ 0x55ece63ac360] The driver changed the time per frame from 1/1 to 1/30
  
  Input #0, video4linux2,v4l2, from '/dev/video0':
  
    Duration: N/A, start: 37064.594605, bitrate: N/A
  
      Stream #0:0: Video: mjpeg, yuvj422p(pc, bt470bg/unknown/unknown), 1920x1080, 30 fps, 30 tbr, 1000k tbn, 1000k tbc

  But this doesnt work.