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• Better performance for ffmpeg decoding editing image contrast for every frame

  6 août 2013, par Simone M

  i'm developing an rtsp player using ffmpeg library and i must edit contrast image for every frame of video, searching the web i found this code for edit contrast :

  - (UIImage*)contrast
  
  {    
  
      CIImage *beginImage = [CIImage imageWithCGImage:[self CGImage]];
  
      CIContext *context = [CIContext contextWithOptions:nil];
  
  
  
      CIFilter *filter = [CIFilter filterWithName:@"CISepiaTone" 
  
                                    keysAndValues: kCIInputImageKey, beginImage, 
  
                          @"inputIntensity", [NSNumber numberWithFloat:0.8], nil];
  
      CIImage *outputImage = [filter outputImage];
  
  
  
      CGImageRef cgimg = 
  
      [context createCGImage:outputImage fromRect:[outputImage extent]];
  
      UIImage *newImg = [UIImage imageWithCGImage:cgimg];
  
  
  
      self = newImg;
  
  
  
      CGImageRelease(cgimg);
  
      return self;
  
  }

  it works perfectly, but on iPad i lose performance and when decoding video are show a lot of noise on screen. There is a better way in performance to modify contrast for image ??

• FFMpeg generating screenshots drop frames

  6 octobre 2011, par Morgan

  I'm using FFMpeg to extract frames from a video file, and for most videos it works flawlessly. But certain videos it seems to have to seek to the position that I want to take the screenshot from, and drops all the frames on the way there taking quite a while if the position i'm generating a screenshot from is near the end of the video. Here is the command I'm using to extract my screenshot.

  ffmpeg -ss 60 -i input.mkv -vframes 1 -f image2 -an -r 1/5 output.jpg

  and the output I receive

  ffmpeg version 0.8.3, Copyright (c) 2000-2011 the FFmpeg developers
  
    built on Sep 20 2011 00:46:47 with clang 2.1 (tags/Apple/clang-163.7.1)
  
    configuration: --prefix=/Users/Morgan/Downloads/installed/ffmpeg --extra-libs=/Users/Morgan/Downloads/installed/lib/libfaac.a --enable-gpl --extra-cflags=-I/Users/Morgan/Downloads/installed/include --disable-ffplay --disable-ffserver --disable-shared --disable-debug --extra-ldflags=-L/Users/Morgan/Downloads/installed/lib --enable-libmp3lame --enable-libfaac --enable-libx264 --enable-nonfree --cc=clang
  
    libavutil    51.  9. 1 / 51.  9. 1
  
    libavcodec   53.  7. 0 / 53.  7. 0
  
    libavformat  53.  4. 0 / 53.  4. 0
  
    libavdevice  53.  1. 1 / 53.  1. 1
  
    libavfilter   2. 23. 0 /  2. 23. 0
  
    libswscale    2.  0. 0 /  2.  0. 0
  
    libpostproc  51.  2. 0 / 51.  2. 0
  
  [matroska,webm @ 0x7f9dd3007c00] Estimating duration from bitrate, this may be inaccurate
  
  
  
  Seems stream 0 codec frame rate differs from container frame rate: 47.95 (500000/10427) -> 23.98 (24000/1001)
  
  Input #0, matroska,webm, from 'input.mkv':
  
    Duration: 01:01:36.16, start: 0.000000, bitrate: 576 kb/s
  
      Stream #0.0(eng): Video: h264 (High), yuv420p, 1280x720, PAR 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
  
      Metadata:
  
        title           : Input Video
  
      Stream #0.1(eng): Audio: ac3, 48000 Hz, 5.1, s16, 384 kb/s (default)
  
      Metadata:
  
        title           : English Dolby Digital 5.1 AC3
  
      Stream #0.2(eng): Audio: ac3, 48000 Hz, stereo, s16, 192 kb/s
  
      Metadata:
  
        title           : Commentary
  
      Stream #0.3(eng): Subtitle: [0][0][0][0] / 0x0000 (default)
  
      Metadata:
  
        title           : English
  
  Incompatible pixel format 'yuv420p' for codec 'mjpeg', auto-selecting format 'yuvj420p'
  
  [buffer @ 0x106c10c00] w:1280 h:720 pixfmt:yuv420p tb:1/1000000 sar:1/1 sws_param:
  
  [buffersink @ 0x106c10e40] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'out'
  
  [scale @ 0x106c11140] w:1280 h:720 fmt:yuv420p -> w:1280 h:720 fmt:yuvj420p flags:0x4
  
  Output #0, image2, to 'output.jpg':
  
    Metadata:
  
      encoder         : Lavf53.4.0
  
      Stream #0.0(eng): Video: mjpeg, yuvj420p, 1280x720 [PAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 0.20 tbc (default)
  
      Metadata:
  
        title           : Input Video
  
  Stream mapping:
  
    Stream #0.0 -> #0.0
  
  Press [q] to stop, [?] for help
  
  frame=    0 fps=  0 q=0.0 Lsize=      -0kB time=00:00:00.00 bitrate=   0.0kbits/s dup=0 drop=275    
  
  video:0kB audio:0kB global headers:0kB muxing overhead -inf%

• How to go from .srt subtitles and a .ts video to a .ts video with dvb_subtitles ?

  19 décembre 2020, par L42

  I'm trying to get from a .srt subtitle file + a .ts video file => a .ts video file with a dvb_subtitle.

  


  My .srt :

  


  1
00:00:00,000 --> 00:00:05,000
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi vel hendrerit massa.

2
00:00:05,000 --> 00:00:10,000
Aliquam dolor sapien, molestie ac sagittis eu, tempus nec est.

3
00:00:10,000 --> 00:00:28,000
Morbi id sem eu sapien consectetur imperdiet. Morbi sed purus et sapien interdum placerat vitae quis orci.


  


  My .ts : sample_1920x1080.ts from https://filesamples.com/formats/ts

  


  SubtitleEdit command : .\SubtitleEdit.exe /convert 'test_subtitles.srt' Blu-raysup /resolution:1920x1080 /overwrite.
This creates a test_subtitles.sup file as expected.

  


  I then use ffmpeg to include the .sup subtitles, like this : .\ffmpeg.exe -y -i 'sample_1920x1080.ts' -fix_sub_duration -i 'test_subtitles.sup' -map 0:v -map 1:s -vcodec copy -acodec copy -scodec dvbsub -copyts -muxdelay 0 -max_delay 0 'output.ts'. This works, but the results are sometimes not very readable. Here's a screenshot :

  


  

  


  Do I have any other options here ? Or options within subtitleedit/ffmpeg to f.ex. make the subtitles be bigger ?

  


  (I've posted this to the SubtitleEdit Github repository as well : https://github.com/SubtitleEdit/subtitleedit/issues/4539.)

  


  UPDATE :

  


  I learned from the author of SubtitleEdit that it's indeed possible to increase the font size if using the graphical user interface of SubtitleEdit (see here. However, I wish to do this using a command line tool.