exiftool-vendored

Fast, cross-platform Node.js access to ExifTool.

Features

Best-of-class cross-platform performance and reliability.

Expect an order of magnitude faster performance than other packages.
Proper extraction of
- dates with correct timezone offset encoding, when available)
- latitudes & longitudes as floats (where negative values indicate west or south of the meridian)
- embedded images, like Thumbnail and Preview (if they exist)
Support for writing tags
Type definitions of the top 99.5% tags used by over 6,000 different camera makes and models
Auditable ExifTool source code (the vendored code is checksum verified)
Automated updates to ExifTool (as new versions come out monthly)
Robust test coverage, performed with the latest Node v6, v8, and v9 on Linux, Mac, & Windows.

Installation

 yarn add exiftool-vendored

 npm install --save exiftool-vendored

Note that exiftool-vendored provides an installation of ExifTool relevant for your local platform through optionalDependencies.

You shouldn't include either the exiftool-vendored.exe or exiftool-vendored.pl as direct dependencies to your project.

Usage

There are many configuration options to ExifTool, but all values have defaults.

Please review the ExifTool constructor parameters and override default values where appropriate.

const { ExifTool } = require("exiftool-vendored");
const exiftool = new ExifTool();

// And to verify everything is working:
exiftool.version().then(version =>
  console.log(`We're running ExifTool v${version}`)
);

General API

ExifTool.read() returns a Promise to a Tags instance. Note that errors may be returned either by rejecting the promise, or for less severe problems, via the errors field.

All other public ExifTool methods return Promise<void>, and will reject the promise if the operation is not successful.

Reading tags

exiftool
  .read("path/to/image.jpg")
  .then((tags /*: Tags */) => console.log(`Make: ${tags.Make}, Model: ${tags.Model}, Errors: ${tags.errors}`))
  .catch(err => console.error("Something terrible happened: ", err))

Extracting embedded images

Extract the low-resolution thumbnail in path/to/image.jpg, write it to path/to/thumbnail.jpg, and return a Promise<void> that is fulfilled when the image is extracted:

exiftool.extractThumbnail("path/to/image.jpg", "path/to/thumbnail.jpg");

Extract the Preview image (only found in some images):

exiftool.extractPreview("path/to/image.jpg", "path/to/preview.jpg");

Extract the JpgFromRaw image (found in some RAW images):

exiftool.extractJpgFromRaw("path/to/image.cr2", "path/to/fromRaw.jpg");

Extract the binary value from "tagname" tag in path/to/image.jpg and write it to dest.bin (which cannot exist already and whose parent directory must already exist):

exiftool.extractBinaryTag("tagname", "path/to/file.exf", "path/to/dest.bin");

Writing tags

Note that only a portion of tags are writable. Refer to the documentation and look under the "Writable" column.

If you apply malformed values or ask to write to tags that aren't supported, the returned Promise will be rejected.

Only string and numeric primitive are supported as values to the object

Write a comment to the given file so it shows up in the Windows Explorer Properties panel:

exiftool.write("path/to/file.jpg", { XPComment: "this is a test comment" });

Change the DateTimeOriginal, CreateDate and ModifyDate tags (using the AllDates shortcut) to 4:56pm UTC on February 6, 2016:

exiftool.write("path/to/file.jpg", { AllDates: "2016-02-06T16:56:00" });

Always Beware: Timezones

If you edit a timestamp tag, realize that the difference between the changed timestamp tag and the GPS value is used by exiftool-vendored to infer the timezone.

In other words, if you only edit the CreateDate and don't edit the GPS timestamps, your timezone will either be incorrect or missing. See the section about Dates below for more information.

Resource hygene

Remember to call .end().

ExifTool processes consume system resources. If you're done with it, turn it off with .end(), which returns a Promise<void> if you want to wait for the shutdown to be complete.

Mocha v4.0.0

If you use mocha v4 or later, and you don't call exiftool.end(), you will find that your test suite hangs. The relevant change is described here, and can be solved by adding an after block that shuts down the instance of ExifTool that your tests are using:

after(() => exiftool.end()) // assuming your singleton is called `exiftool`

Dates

Generally, EXIF tags encode dates and times with no timezone offset. Presumably the time is captured in local time, but this means parsing the same file in different parts of the world results in a different absolute timestamp for the same file.

Rather than returning a Date which always includes a timezone, this library returns classes that encode the date, the time of day, or both, with an optional tzoffset. It's up to you, then, to do what's right.

In many cases, though, a tzoffset can be determined, either by the composite TimeZone tag, or by looking at the difference between the local DateTimeOriginal and GPSDateTime tags. GPSDateTime is present in most smartphone images.

If a tzoffset can be determined, it is encoded in all related ExifDateTime tags for those files.

Note also that some smartphones record timestamps with microsecond precision (not just millis!), and both ExifDateTime and ExifTime have floating point milliseconds.

Performance

The npm run mktags target reads all tags found in a batch of sample images and parses the results.

Using exiftool-vendored:

Read 2236 unique tags from 3011 files.
Parsing took 16191ms (5.4ms / file) # win32, core i7, maxProcs 4
Parsing took 27141ms (9.0ms / file) # ubuntu, core i3, maxProcs 1
Parsing took 12545ms (4.2ms / file) # ubuntu, core i3, maxProcs 4

Using the exiftool npm package takes 7x longer (and doesn't work on Windows):

Reading 3011 files...
Parsing took 85654ms (28.4ms / file) # ubuntu, core i3

Batch mode

Starting the perl version of ExifTool is expensive, and is especially expensive on the Windows version of ExifTool.

On Windows, for every invocation, exiftool installs a distribution of Perl and extracts the ~1000 files that make up ExifTool, and then runs the perl script. Windows virus scanners prevent reads on these files while they are scanned, which makes this approach even more costly.

Using ExifTool's -stay_open batch mode means we can reuse a single instance of ExifTool across many requests, dropping response latency dramatically as well as reducing system load.

Parallelism

To avoid overwhelming your system, the exiftool singleton is configured with a maxProcs set to a quarter the number of CPUs on the current system (minimally 1); no more than maxProcs instances of exiftool will be spawned. If the system is CPU constrained, however, you may want a smaller value. If you have very fast disk IO, you may see a speed increase with larger values of maxProcs, but note that each child process can consume 100 MB of RAM.

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