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• 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 ?

  


• how to let ffplay process whats happening ?

  3 septembre 2023, par boplip

  my ffplay is trying to hard to process something. I sped up my voice in real-time with ffmpeg and I am using ffplay. ffplay is trying to process my voice fast but isn't able to because it cant go past time. someone told me to use -re before -i but that doesnt work. is there a way to get ffplay to process something slower ?

  


  i tried speeding up my voice.

  


  when I pause ffplay and talk then resume it, it works perfect. but when I just let it do it in real-time, the audio starts cutting in and out. I want to be able to not have to pause it to talk fast.

  


• ffmpeg difference between time and rtime, utime

  15 janvier, par nojob

  When I execute a command with "-benchmark" I can get some information like
rtime, utime, stime which are real time, user time and system time respectively.
But I can't understand what are they exactly ?
Because as I know, the real time is the wall clock which means the time that the whole process needs.

  


  And there is another time at the end of the command.

  


  Like below :

  


  

  


  What is the difference between them ?
time : 00:00:00.16
rtime : 0.197s