Google Pixel phones support what they call ”Motion Photo” which is essentially a photo with a short video clip attached to it. They are quite nice since they bring the moment alive, especially as the capturing of the video starts a small moment before the shutter button is pressed. For most viewing programs they simply show as static JPEG photos, but there is more to the files.

I’d really love proper Shotwell support for these file formats, so I posted a longish explanation with many of the details in this blog post to a ticket there too. Examples of the newer format are linked there too.

There are actually two different formats, an old one that is already obsolete, and a newer current format. The older ones are those that your Pixel phone recorded as ”MVIMG_[datetime].jpg", and they have the following meta-data:

Xmp.GCamera.MicroVideo                       XmpText     1  1
Xmp.GCamera.MicroVideoVersion                XmpText     1  1
Xmp.GCamera.MicroVideoOffset                 XmpText     7  4022143
Xmp.GCamera.MicroVideoPresentationTimestampUs XmpText     7  1331607


The offset is actually from the end of the file, so one needs to calculate accordingly. But it is exact otherwise, so one simply extract a file with that meta-data information:

#!/bin/bash
#
# Extracts the microvideo from a MVIMG_*.jpg file

# The offset is from the ending of the file, so calculate accordingly
offset=$(exiv2 -p X "$1" | grep MicroVideoOffset | sed 's/.*\"$$.*$$"/\1/')
filesize=$(du --apparent-size --block=1 "$1" | sed 's/^$$[0-9]*$$.*/\1/')
extractposition=$(expr$filesize - $offset) echo offset:$offset
echo filesize: $filesize echo extractposition=$extractposition
dd if="$1" skip=1 bs=$extractposition of="$(basename -s .jpg$1).mp4"


The newer format is recorded in filenames called ”PXL_[datetime].MP.jpg”, and they have a _lot_ of additional metadata:

Xmp.GCamera.MotionPhoto                      XmpText     1  1
Xmp.GCamera.MotionPhotoVersion               XmpText     1  1
Xmp.GCamera.MotionPhotoPresentationTimestampUs XmpText     6  233320
Xmp.xmpNote.HasExtendedXMP                   XmpText    32  E1F7505D2DD64EA6948D2047449F0FFA
Xmp.Container.Directory                      XmpText     0  type="Seq"
Xmp.Container.Directory[1]                   XmpText     0  type="Struct"
Xmp.Container.Directory[1]/Container:Item    XmpText     0  type="Struct"
Xmp.Container.Directory[1]/Container:Item/Item:Mime XmpText    10  image/jpeg
Xmp.Container.Directory[1]/Container:Item/Item:Semantic XmpText     7  Primary
Xmp.Container.Directory[1]/Container:Item/Item:Length XmpText     1  0
Xmp.Container.Directory[2]                   XmpText     0  type="Struct"
Xmp.Container.Directory[2]/Container:Item    XmpText     0  type="Struct"
Xmp.Container.Directory[2]/Container:Item/Item:Mime XmpText     9  video/mp4
Xmp.Container.Directory[2]/Container:Item/Item:Semantic XmpText    11  MotionPhoto
Xmp.Container.Directory[2]/Container:Item/Item:Length XmpText     7  1679555


Sounds like fun and lots of information. However I didn’t see why the “length” in first item is 0 and I didn’t see how to use the latter Length info. But I can use the mp4 headers to extract it:

#!/bin/bash
#
# Extracts the motion part of a MotionPhoto file PXL_*.MP.mp4

extractposition=$(grep --binary --byte-offset --only-matching --text -P "\x00\x00\x00\x18\x66\x74\x79\x70\x6d\x70\x34\x32"$1 | sed 's/^$$[0-9]*$$.*/\1/')

dd if="$1" skip=1 bs=$extractposition of="$(basename -s .jpg$1).mp4"


UPDATE: I wrote most of this blog post earlier. When now actually getting to publishing it a week later, I see the obvious ie the ”Length” is again simply the offset from the end of the file so one could do the same less brute force approach as for MVIMG. I’ll leave the above as is however for the ❤️ of binary grepping.

(cross-posted to my other blog)