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• blank transparent pngs behave like black canvas

  10 novembre 2015, par Anay Bose

  I am trying to create a scrolling image with imagemagick’s roll and crop functions. Its a frame-by—frame animation. The source image is a transparent png with some text written on it. The following code works and it creates the required frames, including some blank png images at first for a nice, smooth effect. These blank pngs are what creating problems when I am trying to convert my image frames into video with ffmpeg. FFMPEG is seemingly considering these blank pngs as black/dark images, so the resulting video contains a blackout for a few seconds in the beginning—which I do not want.

  I am using png codec with bgra pixel format. My ffmpeg command (shown below) creates smooth, clear animation with images that have some text on it.

  "ffmpeg -i trans/trans-%d.png -vcodec png -pix_fmt bgra overlay-0.mov";

  The blank pngs behave like black canvas, but as I try to write some text on them or surround them with a border (i.e. colorize in some way) the problem disappears—which seems very strange. I have tested all my images ; they are all transparent. For the past few hours, I have been searching for a solution, no luck so far. Please note those blank pngs are required in the beginning for a smooth effect, and I cannot omit them. I have uploaded a sample video in Youtube. Please note the black fade out.

  https://www.youtube.com/watch?v=Te3LuItxcDk&feature=youtu.be

  https://youtu.be/Te3LuItxcDk

  PHP code :

     $increment = 40;
  
     $count = 0; 
  
  
  
     for ($x=40; $x <= 640 ; $x+=$increment) 
  
     {
  
       $roll = new Imagick(DOCROOT . '/composite-0.png');
  
       $roll->rollImage($x, 0);
  
       $roll->writeImage(DOCROOT . '/roll/roll-' . $x . '.png');
  
  
  
      $crop = new Imagick(DOCROOT . '/roll/roll-' . $x . '.png');
  
      $crop->cropImage($x, 720, 0, 0);
  
      $crop->writeImage(DOCROOT . '/roll/crop-' . $x . '.png');
  
  
  
      $extent = new Imagick(DOCROOT . '/roll/crop-' . $x . '.png'); 
  
      # $extent->setImageBackgroundColor(new ImagickPixel('none'));
  
      $extent->setImageBackgroundColor(new ImagickPixel('transparent'));
  
      $extent->extentImage(640, $extent->getImageHeight(), 0, 0);
  
      $extent->setImageFormat('png'); 
  
      $extent->writeImage(DOCROOT . '/trans/trans-' . $count . '.png');
  
  
  
      $count++; 
  
     }

• avfilter/avf_showcwt : do not return initial black frames with negative timestamps

  11 novembre 2023, par Paul B Mahol

  avfilter/avf_showcwt : do not return initial black frames with negative timestamps
  

  • [DH] libavfilter/avf_showcwt.c

• How to add black frames and keep the framerate ?

  3 mars 2020, par Patryk

  I have a black image from which I generate videos filled with black color only for specified lengths that I can then concatenate with my destination videos. This is how I produce it :

  ffmpeg -loop 1 -i black.png -t 00:00:00.066 \ 
  
      -c:v libx264 -pix_fmt yuv420p -vf scale=840:480,fps=15 out66ms.mp4

  with the following ffmpeg output :

  Input #0, png_pipe, from 'black.png':
  
    Duration: N/A, bitrate: N/A
  
      Stream #0:0: Video: png, rgba(pc), 608x342 [SAR 5669:5669 DAR 16:9], 25 fps, 25 tbr, 25 tbn, 25 tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  [libx264 @ 0x7fadf3826e00] using SAR=64/63
  
  [libx264 @ 0x7fadf3826e00] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
  
  [libx264 @ 0x7fadf3826e00] profile High, level 3.0
  
  [libx264 @ 0x7fadf3826e00] 264 - core 155 r2917 0a84d98 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=15 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to 'out66ms.mp4':
  
    Metadata:
  
      encoder         : Lavf58.29.100
  
      Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 840x480 [SAR 64:63 DAR 16:9], q=-1--1, 15 fps, 15360 tbn, 15 tbc
  
      Metadata:
  
        encoder         : Lavc58.54.100 libx264
  
      Side data:
  
        cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
  
  frame=    1 fps=0.0 q=27.0 Lsize=       2kB time=00:00:00.00 bitrate=201107.7kbits/s speed=0.0031x
  
  video:1kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 100.984009%
  
  [libx264 @ 0x7fadf3826e00] frame I:1     Avg QP:12.00  size:   123
  
  [libx264 @ 0x7fadf3826e00] mb I  I16..4: 100.0%  0.0%  0.0%
  
  [libx264 @ 0x7fadf3826e00] 8x8 transform intra:0.0%
  
  [libx264 @ 0x7fadf3826e00] coded y,uvDC,uvAC intra: 0.0% 0.0% 0.0%
  
  [libx264 @ 0x7fadf3826e00] i16 v,h,dc,p: 97%  0%  3%  0%
  
  [libx264 @ 0x7fadf3826e00] i8c dc,h,v,p: 100%  0%  0%  0%
  
  [libx264 @ 0x7fadf3826e00] kb/s:14.76

  I’d like to then concatenate it with videos like this one :

  ffprobe file.ts
  
  Input #0, mpegts, from 'file.ts':
  
    Duration: 00:00:06.67, start: 0.000000, bitrate: 1090 kb/s
  
    Program 1
  
      Metadata:
  
        service_name    : Service01
  
        service_provider: FFmpeg
  
      Stream #0:0[0x100]: Video: h264 (Baseline) ([27][0][0][0] / 0x001B), yuv420p(progressive), 864x480, 90k tbr, 90k tbn, 180k tbc

  but as soon as I concatenate it using concat demuxer like that :

  ffmpeg -y -hide_banner \
  
      -f concat -safe 0 \
  
      -i <(echo "file '$PWD/out66ms.mp4'"; for f in dir/*.ts; do echo "file '$PWD/$f'"; done) \
  
      -c copy \
  
      output.mp

  I get this :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.29.100
  
    Duration: 00:01:41.38, start: 0.000000, bitrate: 170 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 840x480 [SAR 64:63 DAR 16:9], 170 kb/s, 2.67 fps, 2.67 tbr, 15360 tbn, 30 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler

  Which has 2.67 fps whereas not adding this empty black video to concatenation gives the following (desired 15 fps) :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.29.100
  
    Duration: 00:00:17.29, start: 0.000000, bitrate: 1001 kb/s
  
      Stream #0:0(und): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 864x480, 999 kb/s, 15.62 fps, 15.58 tbr, 90k tbn, 180k tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler

  EDIT

  I’ve tried reencoding instead of copying :

  ffmpeg -y -hide_banner \
  
      -f concat -safe 0 \
  
      -i <(echo "file '$PWD/out66ms.mp4'"; for f in dir/*.ts; do echo "file '$PWD/$f'"; done) \
  
      -c:v libx264 -vf scale=840:480,fps=15 \
  
      output.mp

  But I get a similar result :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.29.100
  
    Duration: 00:01:41.00, start: 0.000000, bitrate: 555 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1680x480 [SAR 64:63 DAR 32:9], 554 kb/s, 15 fps, 15 tbr, 15360 tbn, 30 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler

  even though that the fps is set properly the video is too long and slowed down.

  How to properly add those black filled videos to preserve fps or set it to desired value ?