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• doc : delete viterbi.txt

  10 novembre 2013, par Timothy Gu

  doc : delete viterbi.txt
  The description has been moved to the FFmpeg wiki :
  
  https://trac.ffmpeg.org/wiki/ViterbiAlgorithm
  Signed-off-by : Timothy Gu <timothygu99@gmail.com>
  

  • [DH] doc/viterbi.txt

• OpenCV3 returning float FRAME_COUNT

  15 mars 2016, par mprat

  I am using OpenCV3 on OSX with Python 2.7 bindings. However, when I try to read the frame count of my video (a .mp4 video), it returns a float - I am expecting an int. Do I need to compile OpenCV3 with some special flags ? Am I missing some codecs ?

  import cv2
  
  vid = cv2.VideoCapture("vid.mp4")
  
  print vid.get(cv2.CAP_PROP_FRAME_WIDTH)

  And it returns a float.

  Installation details :

  • ffmpeg : brew install ffmpeg --with-dcadec --with-openh264 --with-openjpeg --with-openssl --with-tools --with-x265  --with-zimg --with-libvidstab --with-libvpx
  • opencv3 : brew install opencv3 --with-ffmpeg --with-contrib

• How to save ffmpeg segmets to disk immediately with sub-second intervals ?

  20 octobre 2023, par amfast

  I'm trying to record video on a raspberry and have it save as much as possible (sub-second resolution) in case of a power cutoff.

  


  I use -f segment to save the encoded stream in 100ms segments with the hope that all but the interrupted (by power cutoff) segment will be saved in memory. Unfortunately, when cutting off power, all the destination files (output_0001.mp4, output_0002.mp4, ...) are created, but empty.

  


  To save the files to disk immediately, I added the -strftime 1 option that allows formatting the output filename as time. It seems weird that this is the (only ?) way to trigger immediate saving of files, but it works - untill I try to have segments smaller than 1 second. The problem seems to be that the format string %d, that previously added a sequence number in my output filenames, now represents "day" (i.e. date) and the smallest resolution time format string is %S for second. I saw %f suggested somewhere for smaller resolutions, but it only prints "%f".

  


  The result is that the segmentation part of ffmpeg does create 100ms segments and save them to disk immediately, but the strftime feature gives the output files names that only change every second, so all the interim files are overwritten.

  


  Example of the failing command below. Without the -strftime option this creates nice segments, but does not save them to disk immediately.

  


  libcamera-vid --flush \
    --framerate ${FRAMERATE} \
    --width ${WIDTH} \
    --height ${HEIGHT} \
    -n \
    -t ${TIMEOUT} \
    --codec yuv420 \
    -o - | 
ffmpeg \
    -fflags nobuffer \
    -strict experimental \
    -loglevel debug \
    -flags low_delay \
    -f rawvideo \
    -pix_fmt yuv420p \
    -s:v ${WIDTH}x${HEIGHT} \
    -r ${FRAMERATE} \
    -i - \
    -c:v h264_v4l2m2m \
    -f segment \
    -segment_time 0.1 \
    -segment_format mp4 \
    -reset_timestamps 1 \
    -strftime 1 \
    -b:v ${ENCODING_BITRATE} \
    -g 1 \
    "output_%04d.mp4"


  


  Question :
  
Is there another way besides -strftime to trigger immediate saving ? Or is there a mechanism to feed finer resolution format strings to the output filename ?