How to extract the Photo/Video component of a MVIMG?

Question

The Google Pixel 2 and probably other phones since have the capability to cover "Motion Photos". These are saved as MVIMG and comparatively big.

I’m looking for a way to remove/extract the video.

So far I found a promising exif tag

$ exiftool -xmp:all MVIMG_123.jpg
XMP Toolkit                     : Adobe XMP Core 5.1.0-jc003
Micro Video                     : 1
Micro Video Version             : 1
Micro Video Offset              : 4032524

I thought the video might be present at the specified offset, but this doesn’t work:

$ dd if=MVIMG_123.jpg of=video.mp4 bs=4032524 skip=1
$ file video.mp4
video.mp4: data

Are there any resources that document the embedding? Are there even any tools to remove/extract the video?

Answer 1

I did find https://github.com/cliveontoast/GoMoPho which scans for the mp4 header and then dumps the video.

We can do the same, scanning for ftypmp4 from the MP4 header (actual file starts 4 bytes earlier):

Thus to extract videos:

for i in MVIMG*.jpg; do \
  ofs=$(grep -F --byte-offset --only-matching --text ftypmp4 "$i"); \
  ofs=${ofs%:*}; \
  [[ $ofs ]] && dd "if=$i" "of=${i%.jpg}.mp4" bs=$((ofs-4)) skip=1; \
done

And to remove videos:

for i in MVIMG*.jpg; do \
  ofs=$(grep -F --byte-offset --only-matching --text ftypmp4 "$i"); \
  ofs=${ofs%:*}; \
  [[ $ofs ]] && truncate -s $((ofs-4)) "$i"; \
done

Answer 2

The EXIF tag is useful, but the offset is with the respect to the end of the file. The mp4 file is embedded at:

[file_size-micro_video_offset, file_size)

For example:

$ exiftool -xmp:all MVIMG_123.jpg
XMP Toolkit                     : Adobe XMP Core 5.1.0-jc003
Micro Video                     : 1
Micro Video Version             : 1
Micro Video Offset              : 2107172
Micro Video Presentation Timestamp Us: 966280
$ python -c 'import os; print os.path.getsize("MVIMG_123.jpg") - 2107172'
3322791
$ dd if=MVIMG_123.jpg of=video.mp4 bs=3322791 skip=1
$ file video.mp4 
video.mp4: ISO Media, MP4 v2 [ISO 14496-14]