This question is about extraction of metadata only.
Is it required for exiftool to get a complete file for propperly working?
Scenario:
I want to extract the metadata of a 20 GB video file. Do I need to provide exiftool with the complete file (via stdin), or is it enough to provide it with a certain amount of bytes.
Motivation:
I am programatically (golang) calling exiftool in a streaming context and want to have the extraction as fast as possible. Magic numbers for filetypes work with the first 33 bytes and I am wondering if that is possible with the exiftool metadata as well.
The answer depends upon the file and the location of the metadata within that file.
There are a couple of threads on the subject on the ExifTool forums (link 1, link 2) and Phil Harvey, the author, says that about half the time the in the case of MP4/MOV videos, the metadata is at the end of the file.
Using the -fast option might help. I've done some quick tests using cURL and a large image file (see the second to the last example under Piping Examples) and in that case cURL didn't download the whole image file, just enough to extra the metadata. It might be different with a video file though, as I haven't tested that situation.