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• Macros in C++ / FFMPEG

  26 mars 2020, par Derrick Heimerdinger

  I’m new to C++ and I’m trying to build a custom codec for FFMPEG. I’m trying to base it off of PCM but with only one type. I’ve run into a macro and I have no idea what the macro turns into after it compiles.
  The macro looks like this :

  #define ENCODE_PLANAR(type, endian, dst, n, shift, offset)          \
  
  n /= avctx->channels;                                               \
  
  for (c = 0; c < avctx->channels; c++) {                             \
  
      int i;                                                          \
  
      samples_ ## type = (const type *) frame->extended_data[c];      \
  
      for (i = n; i > 0; i--) {                                       \
  
          register type v = (*samples_ ## type++ >> shift) + offset;  \
  
          bytestream_put_ ## endian(&dst, v);                         \
  
      }                                                               \
  
  }

  Would the samples_ declaration line and bytestream_put line be equal to what I put below if endian = byte and type = uint8_t ?

  uint8_t samples_ = (const uint8_t *) frame->extended_data[c];
  
  bytestream_put_byte(&dst, v);

  I find it very confusing and I am unsure if this is correct.

• 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 ?

  


• ExoPlayer and deinterlacing feature

  21 février 2021, par Suppaman

  I want to use ExoPlayer to show interlaced video but, especially for SD content, the video looks really bad without any deinterlacing feature. Looking in the ExoPlayer project it seem the player doesn't have such deinterlacing feature and doesn't seem in plan to be added. I'm thinking to try add deinterlacing by using the deinterlacing engine of ffmpeg library. However it don't seem and easy task. I found some projects that could help me like this ExoPlayerFilter that apply a filter on the frame before show. This could be a possible way to "deinterlace" the frame before show. Another possible suggestion comes from the tread in github Exoplayer project here. This could be another possible way to proceed. My problem is that I have a limited time to try add this feature and I would to know from people having more experience than me what would be most "suggested" way to follow or if someone know another better way to reach my results.

  


  Thank you