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• calc_avgy8 from ffmpeg need explanation

  15 mai 2020, par user3524642

  I want to implement my own deflicker so I took a look into ffmpeg library as an example. During deflicker it calculates the average pixel luminance.

  



  The calc_avgy8 (from deflicker.c) function seems to compute histogram and the mean of the histogram :

  



  static float calc_avgy8(AVFilterContext *ctx, AVFrame *in)
{
    DeflickerContext *s = ctx->priv;
    const uint8_t *src = in->data[0];
    int64_t sum = 0;
    int y, x;

    memset(s->histogram, 0, (1 << s->depth) * sizeof(*s->histogram));

    for (y = 0; y < s->planeheight[0]; y++) {
        for (x = 0; x < s->planewidth[0]; x++) {
            s->histogram[src[x]]++;
        }
        src += in->linesize[0];
    }

    for (y = 0; y < 1 << s->depth; y++) {
        sum += s->histogram[y] * y;
    }

    return 1.0f * sum / (s->planeheight[0] * s->planewidth[0]);
}


  



  To my mind the mean of an histogram is the same as a mean pixel. Can't it be simplified as the below code ?

  



  static float calc_avgy8(AVFilterContext *ctx, AVFrame *in)
{
    DeflickerContext *s = ctx->priv;
    const uint8_t *src = in->data[0];
    int64_t sum = 0;
    int y, x;

    memset(s->histogram, 0, (1 << s->depth) * sizeof(*s->histogram));

    for (y = 0; y < s->planeheight[0]; y++) {
        for (x = 0; x < s->planewidth[0]; x++) {
            s->histogram[src[x]]++;
            sum += src[x];
        }
        src += in->linesize[0];
    }

    return 1.0f * sum / (s->planeheight[0] * s->planewidth[0]);
}


  


• Révision 19188 : utiliser cURL si present pour lancer la requete asynchrone vers action=cron pour...

  2 avril 2012, par cedric -

• movenc : Present durations in mvhd/tkhd/mdhd as they are after edits

  19 décembre 2020, par Martin Storsjö

  movenc : Present durations in mvhd/tkhd/mdhd as they are after edits
  If the edit lists remove parts of the output timeline, or add a
  
  delay to it, this should be included in the mvhd/tkhd/mdhd durations,
  
  which should correspond to the edit lists.
  For tracks starting with pts < 0, the edit list trims out the segment
  
  before pts=0. For tracks starting with pts > 0, a delay element is
  
  added in the edit list, delaying the start of the track data.
  In both cases, the practical effect is that the post-edit output
  
  is as if the track had started with pts = 0. Thus calculate the range
  
  from pts=0 to end_pts, for the purposes of mvhd/tkhd/mdhd, unless
  
  edit lists explicitly are disabled.
  mov_write_edts_tag needs to operate on the actual pts duration of
  
  the track samples, not the duration that already takes the edit
  
  list effect into account.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavformat/movenc.c
  • [DH] tests/ref/fate/copy-trac3074
  • [DH] tests/ref/fate/gaplessenc-itunes-to-ipod-aac
  • [DH] tests/ref/fate/gaplessenc-pcm-to-mov-aac
  • [DH] tests/ref/fate/movenc