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• Reading colors encoded in image at a position changes its value after decoded from video using php and ffmpeg

  29 novembre 2022, par Jeenus Junanio

  I created a piece of code to encode unique color on image and converted the image to PNG so that it would be lossless. After This I created a video with the frame using this image using the ffmpeg in php shellexec(). After saving this video I reopened it to extract the frmae image added and tried to read those values from the image. Now the values on the image are a bit changed.

  


  Here is the code that I tried to create the video :

  


  $canvas = imagecreatefromjpeg('translate/first_frame.jpg');
        // create a random color
        $rand = str_pad(dechex(rand(0x000000, 0xFFFFFF)), 6, 0, STR_PAD_LEFT);
        $dec_color= hexdec($rand);

        // add the new color to image

        for ($i=0; $i < 24; $i++) { 
           imagesetpixel($canvas,$i,0,$dec_color);
        }

        // store the image and close the file opened

        // $filename = 'translate/test/output.png'; 
        $filename = 'translate/test/output.bmp'; 

        // imagepng($canvas, $filename);
        imagebmp($canvas, $filename);

        imagedestroy($canvas);

        $frame      = $filename; // an image(png,gif,etc)
        $audio      = 'translate/output/audio/abcdefghijklmnopqrstuvwxya.mp3';
        $output     = 'translate/output/video/'.time().'.mp4';   

        $cmd = 'ffmpeg -loop 1 -y -i '.$frame.' -i '.$audio.' -c:v libx264 -tune stillimage -c:a copy -shortest '.$output;
        shell_exec($cmd);


  


  This above code is creating the video with the image.

  


  Now I tried to extract the image video and color from image, the colors are a bit changed.

  


  if($request->hasFile(&#x27;video&#x27;)){&#xA;            $file = $request->file(&#x27;video&#x27;);&#xA;            $filename = $file->getClientOriginalName();&#xA;            $path = public_path(&#x27;translate/test/&#x27;);&#xA;        }else{&#xA;            return &#x27;No file uploaded&#x27;;&#xA;        }&#xA;        &#xA;        &#xA;        if ($file->move($path, $filename)) {&#xA;            $video = &#x27;translate/test/&#x27;.$filename;&#xA;        }else{&#xA;            return &#x27;error file upload&#x27;;&#xA;        }&#xA;&#xA;       &#xA;        // $output = &#x27;translate/output/image/&#x27;.time().&#x27;.png&#x27;;&#xA;        $output = &#x27;translate/output/image/&#x27;.time().&#x27;.bmp&#x27;;&#xA;        // $output = &#x27;translate/output/image/&#x27;.time().&#x27;.jpg&#x27;;&#xA;&#xA;        $cmd = &#x27;ffmpeg -i &#x27;.$video.&#x27; -vframes 1 &#x27;.$output;&#xA;        shell_exec($cmd);&#xA;&#xA;&#xA;// $dimg = imagecreatefrompng($output);&#xA;        $dimg = imageCreateFromBmp($output);&#xA;        // $dimg = imagecreatefromjpeg($output);&#xA;&#xA;        $extracted_color = array();&#xA;&#xA;        for ($x=0; $x &lt; 24 ; $x&#x2B;&#x2B;) { &#xA;          $extracted_color[]= imagecolorat($dimg, $x, 0);&#xA;        }&#xA;&#xA;        echo "<br />Retrived colors:<pre>".print_r($extracted_color,1)."</pre>";&#xA;&#xA;        imagedestroy($dimg);&#xA;&#xA;&#xA;&#xA;

  


  The color added was 44743072 but the colors retrieved are 4539914,4474121,4408072,4408326 from x=0,y=0 to x=24,y=0.

  


  In both PNG and BMP I am loosing the added pixels. You can clearly see in my code i have commented the code for png to read the image as bmp.

  


  Can someone let me know if I miss anything here.

  


• How does ffmpeg divide into frames EXACTLY

  6 décembre 2022, par JFCorleone

  I'm using this piece of code in python to split a video into frames.

  


      def ffmpeg(self, video_file, fps, start_number, **trim_kwargs):
        ffmpeg.input(video_file) \
            .filter('fps', fps=fps) \
            .trim(**trim_kwargs) \
            .output(os.path.join(self._output_dir, f"%0{NAME_PADDING}d.JPG"),
                    **{'qscale:v': 1, 'vsync': 'drop', 'start_number': start_number}) \
            .run()


  


  I sometimes use also trimming options more or less like this :

  


  ffmpeg(video_file, fps, 0, start=XXX,end=YYY)


  


  Additionally, I have a list with timestamps (starting from point zero) with some additional metadata at certain points. I'm trying to figure out what are the mechanics of ffmpeg of using fps for dividing into frames (for example fps = 1), because when I try to jump through my timestamped log manually with the same "fps", I often get less entries than ffmpeg by 1. It's like ffmpeg always took first and last frame or something. Can someone explain to me how it's done exactly, so I could match metadata with generate frames in the best manner ?

  


• Is it possible to merge multiple FFMPEG commands (cuts, slow down, watermark) into one in order to increase performance ?

  14 novembre 2022, par Nectarie PF

  I wrote a small piece of software in PHP, using FFMPEG commands via shell exec. The final purpose is to take a 7 seconds MP4 file from a GoPro and transform it in order to achieve a sort of boomerang effect :

  


  

  • crop the video to 1080 width/height

  


  


  ffmpeg -i ./files/video_small/$latestVideo -filter:v \"crop=1080:1080:420:0\" ./files/video_small/outcrop_$cod.mp4 2>&1");


  


  

  • first second should run normally

  


  


  ffmpeg.exe -t 1 -i ./files/video_small/outcrop_$cod.mp4 ./files/video_small/out1_$cod.mp4 2>&1");


  


  

  • the next two seconds will run at slow motion with a 2x factor

  


  


  ffmpeg.exe -ss 00:00:01 -t 2 -i ./files/video_small/outcrop_$cod.mp4 -filter_complex \"[0:v]setpts=2*PTS[v]\" -map \"[v]\" ./files/video_small/out2_$cod.mp4 2>&1");


  


  

  • the next second will speed up at 4x factor

  


  


  ffmpeg.exe -ss 00:00:03 -t 1 -i ./files/video_small/outcrop_$cod.mp4 -filter_complex \"[0:v]setpts=0.25*PTS[v]\" -map \"[v]\" ./files/video_small/out3_$cod.mp4 2>&1");


  


  

  • the next 2 seconds again slow motion

  


  


  ffmpeg.exe -ss 00:00:04 -t 2 -i ./files/video_small/outcrop_$cod.mp4 -filter_complex \"[0:v]setpts=2*PTS[v]\" -map \"[v]\" ./files/video_small/out4_$cod.mp4 2>&1");


  


  

  • final second again normal speed

  


  


  ffmpeg.exe -ss 00:00:06 -i ./files/video_small/outcrop_$cod.mp4 ./files/video_small/out5_$cod.mp4 2>&1");


  


  

  • concatenate the above parts to achieve the modified clip

  


  


  ffmpeg.exe -f concat -i ./files/video_small/files_$cod.txt -c copy  ./files/video_small/output1_$cod.mp4 2>&1");


  


  

  • then append the resulting clip in reverse

  


  


  ffmpeg -i ./files/video_small/output1_$cod.mp4 -filter_complex \"[0:v]reverse,fifo[r];[0:v][r] concat=n=2:v=1 [v]\" -map \"[v]\" ./files/video_small/output2_$cod.mp4 2>&1");


  


  

  • add watermark

  


  


  ffmpeg -i ./files/video_small/output2_$cod.mp4 -i ./files/watermark-video1080.png -filter_complex \"[0:v][1:v]overlay=(W-w)/2:10[outv]\" -map [outv] -c:v libx264 -crf 22 -preset veryfast ./files/video_small/output3_$cod.mp4 2>&1");


  


  

  • add audio (we can discard the original audio in any of the above steps)

  


  


  ffmpeg -i ./files/video_small/output3_$cod.mp4 -i ./files/video_small/sound-hip-hop.mp3 -map 0 -map 1:a -c:v copy -shortest ./files/video_small/output_final_$latestVideo 2>&1");


  


  Right now it runs ok, but I have a problem with performance, the whole process lasts about 50 seconds on my 8th gen i7.

  


  I am very new to the capabilities of ffmpeg and I was wondering if any of the below commands can be optimized or if any of the steps can be merged into one, as I can see the syntax is quite powerful.

  


  Thanks !

  


  I was expecting this to run a little bit faster, ideally half the time it takes right now.
As far as I have observed, the longest part is appending the resulting clip in reverse, perhaps I am adding something too heavy and unnecessary in the reverse filter.