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• C pointer casting to and from Go

  26 avril 2018, par nevernew

  I’m writing an app for the windows platform using FFmpeg and it’s golang wrapper goav, but I’m having trouble understanding how to pass the C pointers between C and Go.

  I’ve stripped out all the relevant parts of the C code, the wrapper and my code, shown below :

  C code - libavutil/frame.h

  #include 
  
  
  
  typedef struct AVFrame {
  
  #define AV_NUM_DATA_POINTERS 8
  
      uint8_t *data[AV_NUM_DATA_POINTERS];
  
  }

  Go goav wrapper

  package avutil
  
  
  
  /*
  
      #cgo pkg-config: libavutil
  
      #include <libavutil></libavutil>frame.h>
  
      #include 
  
  
  
      // C code I added:
  
      #include 
  
  
  
      void SaveFrame(const char* location, uint8_t *data, int width, int height) {
  
          FILE *pFile;
  
          int  y;
  
  
  
          // Open file
  
          pFile=fopen(location, "wb");
  
          if(pFile==NULL)
  
              return;
  
  
  
          // Write header
  
          fprintf(pFile, "P6\n%d %d\n255\n", width, height);
  
  
  
          // Write pixel data
  
          for(y=0; y/ Close file
  
          fclose(pFile);
  
      }
  
  */
  
  import "C"
  
  import (
  
      "unsafe"
  
  )
  
  
  
  type Frame C.struct_AVFrame
  
  
  
  func Data(f *Frame) *uint8 {
  
      // i think this is the function thats not working?
  
      return (*uint8)(unsafe.Pointer((*C.uint8_t)(unsafe.Pointer(&amp;f.data))))
  
  }
  
  func SaveFrame(location string, data *uint8, width int, height int) {
  
      C.SaveFrame(C.CString(location), unsafe.Pointer(data), C.int(width), C.int(height))
  
  }

  My Go code

  package main
  
  
  
  import "github.com/giorgisio/goav/avutil"
  
  
  
  func main() {
  
      var frame *avutil.Frame
  
      var data *uint8
  
  
  
      //... initialize frame
  
  
  
      data = avutil.Data(frame)
  
      avutil.SaveFrame("frame0.ppm", data, 1920, 1080)
  
  }

  When I try to save the frame, the resulting image is garbled because the pointer is wrong, how do i fix this ?

• mp4 Vj Animation video lagging hi res video

  21 février 2020, par Ryan Stone

  I am trying to get a video to play inside a video tag at the top left hand corner of my page, it loads ok, the resolution is good and it seems to be looping but it is lagging very much, definatly not achieving 60fps it is in mp4 format and the resolution on the original mp4 is 1920x1080 it is a hi resolution vj free loop called GlassVein, you can see it if you search on youtube. On right clicking properties it comes up with the following inforamtion ;

  Bitrate:127kbs
  Data rate:11270kbps
  Total bitrate:11398kbs
  Audio sample rate is : 44khz
  filetype is:VLC media file(.mp4)
  (but i do not want or need the audio)

  & it also says 30fps, but I’m not sure i believe this as it runs smooth as butter on vlc media player no lagging, just smooth loop animation

  I have searched on :https://trac.ffmpeg.org/wiki/Encode/AAC for encoding information but it is complete gobbldygook to me, I don’t understand a word its saying

  My code is so far as follows ;

      <video src="GlassVeinColorful.mp4" autoplay="1" preload="auto" class="Vid" width="640" height="360" loop="1" viewport="" faststart="faststart" mpeg4="mpeg4" 320x240="320x240" 1080="1080" 128k="128k">  
  
      </video>

  Does anyone know why this is lagging so much, or what I could do about it.
  it is a quality animation and I don’t really want to loose an of its resolution or crispness.. the -s section was originally set to 1920x1080 as this is what the original file is but i have changed it to try and render it quicker...

  Any helpful sites, articles or answers would be great..

  2020 Update

  The Solution to this problem was to convert the Video to WebM, then use Javascript & a Html5 Canvas Element to render the Video to the page instead of using the video tag to embed the video.

  Html

  <section>
  
          <video src="Imgs/Vid/PurpGlassVein.webm" type="video/webm" width="684" height="auto" muted="muted" loop="loop" autoplay="autoplay">
  
                 <source>
  
                 <source>
  
                 <source>
  
          </source></source></source></video>
  
          <canvas style="filter:opacity(0);"></canvas>
  
  </section>

  Css

  video{
  
     display:none !important;
  
     visibility:hidden;
  
  }

  Javascript

      const Canv = document.querySelector("canvas");
  
      const Video = document.querySelector("video");
  
      const Ctx = Canv.getContext("2d");
  
  
  
      Video.addEventListener('play',()=>{
  
        function step() {
  
          Ctx.drawImage(Video, 0, 0, Canv.width, Canv.height)
  
          requestAnimationFrame(step)
  
        }
  
        requestAnimationFrame(step);
  
      })
  
  
  
      Canv.animate({
  
          filter: ['opacity(0) blur(5.28px)','opacity(1) blur(8.20px)']
  
      },{
  
          duration: 7288,
  
          fill: 'forwards',
  
          easing: 'ease-in',
  
          iterations: 1,
  
          delay: 728
  
      })

  I’ve Also Used the Vanilla Javascript .animate() API to fade the element into the page when the page loads. But one Caveat is that both the Canvas and the off-screen Video Tag must match the original videos resolution otherwise it starts to lag again, however you can use Css to scale it down via transform:scale(0.5) ; which doesn’t seem to effect performance at all.

  runs smooth as butter, and doesn’t loose any of the high resolution image.
  Added a slight blur 0.34px onto it aswell to smooth it even more.

  Possibly could of still used ffmpeg to get a better[Smaller File Size] WebM Output file but thats something I’ll have to look into at a later date.

• ffmpeg cross fade 2 pictures in 1080p

  11 mai 2018, par user3574681

  I use this command to fade 2 pictures and it work perfect with 1024 × 768 test pictures.

  ffmpeg -loop 1 -i 1-test.jpg -loop 1 -i 2-test.jpg -filter_complex "[1:v][0:v]blend=all_expr='A*(if(gte(T,3),1,T/3))+B*(1-(if(gte(T,3),1,T/3)))'" -t 4 frames_%04d.png

  But with my original pictures in 1920 × 1080 this error shows up :

  [Parsed_blend_0 @ 0x97c8240] First input link top parameters (size 1920x1080, SAR 0:1) do not match the corresponding second input link bottom parameters (1920x1080, SAR 1:1)
[Parsed_blend_0 @ 0x97c8240] Failed to configure output pad on Parsed_blend_0

  Why is this happening and how can I fix it ?
  Thank you for helping !