[Elphel-support] EXIF data from .mov file + other questions

[Brian Burke]

I don't know if this is the "best" way, but I extracted individual .jpg's (including EXIF data) from a .mov container for a project I did.  I used PHP (and the disclaimer - I'm no PHP pro, so please excuse any bad form).  It's worth noting - I did this processing off-camera, as it's a little processor-intensive.  Also - I was working with .mov clips with no more than 10,000 individual jpg's in them.  If you're recording ~30 fps, then that's a clip only ~5 min long.

First, I read in the .mov:

  //Open the mov
  $fp = @fopen($filename, 'rb');

  if ($fp) {
    //Read the mov
    $mov = fread($fp, filesize($filename));
    fclose($fp);

Then I found all the SOI (Start Of Image) and EOI (End Of Image) markers in the .mov:

    //Find all SOI markers; record them in $soi
    $soiCount = preg_match_all ('/\xff\xd8/', $mov, $soi, PREG_OFFSET_CAPTURE);
    if ($soiCount) {

      //Find all EOI markers; record them in $eoi
      $eoiCount = preg_match_all ('/\xff\xd9/', $mov, $eoi, PREG_OFFSET_CAPTURE);
      if ($eoiCount) {

Then I was able to use the SOI and EOI locations to grab each jpg "chunk" from the .mov:

        //Make sure number of SOI's and EOI's matches
        if ($soiCount == $eoiCount) {

          for ($i=0; $i<count($soi[0]) ; $i++) {

            //This will be a jpg, in binary, parsed from the $mov
            $jpg = substr($mov, $soi[0][$i][1], $eoi[0][$i][1] - $soi[0][$i][1] + 2);

            //Write that image to disk here
  
          }
        }

Now, I didn't implement that "Write that image to disk here" section above, but it should be (but I haven't tried it) as simple as:

      //Write the jpg to the disk
      $tmpImage = 'tmp' . microtime(true) . '.jpg';
      file_put_contents($tmpImage, $jpg);

Once the image is on the disk, you should be able to read the EXIF data into an array (assuming you have the PHP package "exif" installed) with something like:

      $exif = exif_read_data($tmpImage, 'IFD1');

I was only interested in the date/time info, but assuming the Geo info is there, it should just be a matter of reading the correct array element.  For the date/time the image was captured, I used:

      //DateTimeOriginal is in the format "YYYY:MM:DD HH:MM:SS"
      list($date, $time) = explode(" ", $exif['DateTimeOriginal']);

Hope that helps get you started.


  ----- Original Message -
  ---- 
  From: Bader AlKahtani 
  To: support-list 
  Sent: Tuesday, March 01, 2011 9:24 AM
  Subject: [Elphel-support] EXIF data from .mov file + other questions


  Dear All,


  I hope all is well.


  Thanks a lot for all the support on the mailing list. I have been reading the threads trying to answer my questions and I was hoping if I could get some additional help with the following.


  1) Splitting a video file to individual jpegs and linking Geo information to each jpeg. What is the best practice for doing so? I read that recording a .mov then extracting the exif data is a solution but how would that be done - I would really love a step-by-step (I read that there is a php that does this, can you forward that to me?).


  2) If I would like to have an ultimate end product of a series of jpegs (multiple per second) with Geo information attached, would be taking a video and then linking the geo data post production the best approach?


  3) I read in one of the threads about not needing to record a KML file in order to geotag video frames and it also because it might make the processor to go over capacity. What would I need to do to disable the KML file? Do I uncheck geotagging in the Disk writing tool? Or do I uncheck 'Save Exif Data' in the advanced tab?


  4) How do I upgrade the SD Card? Where is the slot? Do I need to actually take apart the case?




  Thanks a lot and looking forward to hearing back from you.


  -- 


  ________________________________
  Bader K. AlKahtani  

  E-mail: Bader at Kahtani.com

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