ExifTool Forum

Hello All,

I would like to write a web application that allows us to analyze the file before it is uploaded. This is to save our users the frustration of us rejecting a 10 gig video file because of an incorrect setting.
I am able to extract any number of bytes from a local file already (in javascript) using :


var blob = file.slice(startingByte, endindByte);
reader.readAsBinaryString(blob);

or

var byteArray= reader.readAsDataURL(blob);


There is a nifty javascript library https://github.com/exif-js/exif-js based on Exiftool that only allows image analysis currently, and The above code works with that, if I for example extract the first 1000 bytes of an image and run it through the library it is able to show me all the exif data.

So I am hoping I could do the same with large videos, I attempted to grab the first 1000 bytes of a video file as a bytearray then I converted it to a base64 string, then I passed it to my backend where I   decoded it to a binary file and then ran that file through the exiftool.exe but it failed to anaylize.

I assume I am either barking up the wrong tree or I don't fully understand one or many of the implications of what I am trying to achieve.

If anyone would be able to assist me I would be most grateful.

Is what I am trying to do possible? if so.. what would you recommend?

Thanks

This may work with some video types where the metadata is stored at the beginning of the image (but I would take the first few MB, not just 1 kB).  However I would say that it won't work for maybe 40% of videos because it is fairly common for the metadata to be stored at the end of the file.

- Phil

Thanks Phil, I appreciate the response.

I managed to get it to work (mostly).. Is there anyway to tell how many bytes I should extract by analyzing any specific bytes at the start?
IE: is there an indicator how long the meta/exif data is and where to find it if possible.

Kind regards 

If the metadata is at the start, you only need to load up to the 'mdat' atom in MOV/MP4 videos.  Usually this works for MOV, but I think MP4 more often has metadata at the end.

- Phil