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• ffmpeg libavfilter acrossfade : I jget just first input in output

  29 juillet 2024, par Alex

  I'm trying to combine two raw audio chunks (s16, 48000, mono) through acrossfade.

  


  I create filter nodes (skip all error checking here) :

  


  avfilter_graph_create_filter(&mediaIn_1,
    avfilter_get_by_name("abuffer"),
    "MediaIn_1",
    "sample_rate=48000:sample_fmt=s16:channel_layout=mono",
    NULL, graph);
avfilter_graph_create_filter(&mediaIn_2,
    avfilter_get_by_name("abuffer"),
    "MediaIn_2",
    "sample_rate=48000:sample_fmt=s16:channel_layout=mono",
    NULL, graph);
avfilter_graph_create_filter(&mediaOut,
    avfilter_get_by_name("abuffersink"),
    "MediaOut",
    NULL, NULL, graph);
avfilter_graph_create_filter(&crossfade,
    avfilter_get_by_name("acrossfade"),
    "crossfade", "nb_samples=6000:c1=tri:c2=tri", NULL, graph);


  


  Then I link them in a graph :

  


  avfilter_link(mediaIn_1, 0, crossfade, 0);
avfilter_link(mediaIn_2, 0, crossfade, 1);
avfilter_link(crossfade, 0, mediaOut, 0);
avfilter_graph_config(graph, NULL);


  


  After that I create a frame with all the chunk data :

  


  frame1 = av_frame_alloc();
frame1->format = AV_SAMPLE_FMT_S16;
frame1->nb_samples = buf1sz / 2;
frame1->sample_rate = 48000;
frame1->ch_layout.order = AV_CHANNEL_ORDER_NATIVE;
frame1->ch_layout.nb_channels = 1;
frame1->ch_layout.u.mask = AV_CH_LAYOUT_MONO;
frame1->ch_layout.opaque = NULL;
frame1->pts = 0;
frame1->duration = buf1sz / 2;
frame1->time_base.num = 1;
frame1->time_base.den = 48000;

av_frame_get_buffer(frame1, 0);
memcpy(frame1->buf[0]->data, buf1, buf1sz);


  


  Same for second chunk.
And send frames into each input buffer :

  


  av_buffersrc_add_frame_flags(mediaIn_1, frame1, 0);
av_buffersrc_add_frame_flags(mediaIn_1, NULL, AV_BUFFERSRC_FLAG_PUSH);

...
av_buffersrc_add_frame_flags(mediaIn_2, frame2, 0);
av_buffersrc_add_frame_flags(mediaIn_2, NULL, AV_BUFFERSRC_FLAG_PUSH);


  


  Then I'm getting output frame :

  


  oframe = av_frame_alloc();
av_buffersink_get_frame_flags(mediaOut, oframe, 0);
...
av_frame_unref(oframe);


  


  The oframe contains (frame1->nb_samples - 6000) number of samples instead of (frame1->nb_samples + frame2->nb_samples - something_for_xfade_needs).
Next call to av_buffersink_get_frame_flags returns AVERROR_EOF.

  


  What is wrong with this algorithm ?

  


  I tried afade filter with "t=in" input and it works fine. I think the problem is with two inputs. I don't get it.

  


• swscale : add two spatially stable dithering methods

  23 mars 2014, par Øyvind Kolås

  swscale : add two spatially stable dithering methods
  Both of these dithering methods are from http://pippin.gimp.org/a_dither/ for
  
  GIF they can be considered better than bayer (provides more gray-levels), and
  
  spatial stability - often more than twice as good compression and less visual
  
  flicker than error diffusion methods (the methods also avoids error-shadow
  
  artifacts of diffusion dithers).
  These methods are similar to blue/green noise type dither masks ; but are
  
  simple enough to generate their mask on the fly. They are still research work
  
  in progress ; though more expensive to generate masks (which can be used in a
  
  LUT) like ’void and cluster’ and similar methods will yield superior results
  

  • [DH] doc/scaler.texi
  • [DH] libswscale/options.c
  • [DH] libswscale/output.c
  • [DH] libswscale/swscale_internal.h
  • [DH] libswscale/utils.c

• ffmpeg 180 degree panoramic fisheye image to equirectangular / flat

  7 juillet 2024, par Willy62

  I am trying to get my Hikvision Panovu image of a sportsfield to look like a standard camera image, similar to what would be seen with a Veo solution / traditional camera.

  


  This is what the image would ideally look like with a little bit of zoom. Note the players are all upright and it looks "correct" and not skewed with the far end of the field in line with the horizon.

  


  veo sample image

  


  The original image looks like this (same field but other side). This is a 180 degree panoramic image from a Hikvision camera as found here.

  


  It provides the following output natively.

  


  hikvision native view

  


  I have had some luck converting the image with ffmpeg using the v360 filter. Note there is a downward tilt meaning I have to apply some yaw to correct it.

  


  v360=input=fisheye:output=rectilinear:ih_fov=180:iv_fov=87.5:d_fov=87.5:pitch=20:yaw=5:w=3840:h=2160


  


  And this gets the following output :

  


  deskewed v360 image

  


  So the challenge here to make the original image flat/equirect but to address the skew such that :

  


  

  • the players are orientated "upright"

  


  • the far sideline of the field looks like a straight line in line with the horizon

  


  • the image quality is preserved as best as possible

  


  


  With these cameras the image is 32MP so there is the opportunity to do an ePTZ into the area of interest.

  


  I suspect v360 isnt the right choice here and it is some remap-style filter, or perhaps I am best going across to gstreamer or similar.

  


  I tried an ffmpeg v360 filter and it partially works, but the players are still skewed because the top of the image is not wide enough. The issue can possibly be solved by correctly applying a couplex perspective filter, but I think this will only mask the issue and perspective requires a complex filter that hasn't worked for me so far.