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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 ?

  


• Save changed frame in FFMPEG API

  23 mars 2015, par Vaigard

  I extracts frames from H.264 video by avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet); procedure (like in example from https://github.com/chelyaev/ffmpeg-tutorial/blob/master/tutorial01.c) and changed values of samples. How I can save these changes in original video ? After the change of the frame by the pointer he does not change.

  And I have a problem with avcodec_encode_video2 function : assertion avctx->codec->encode2 failed at .... What does this mean ?

  Thank you.

• ffmpeg how to save stream to disk and restream at the same time [duplicate]

  24 juin 2020, par jackyyy

  For example, I have a url 'http://www.stream_on_internet.com/index.m3u8',
I know how to save it to disk

  


  ffmpeg -i url -c copy index.mkv

  


  but I want to broadcast it on my local network at the same time

  


  http://192.168.1.1:8080/index.m3u8

  


  so could anyone tell me how to do it ?