dataset2database 0.1

Useful converter of videos to SQL databases for Python

dataset2database

About

The package is made as a solution when using video inputs in Machine Learning models. As extracting and storing frames in .JPEG files will quickly increase the memory requirements and more importantly the number of inodes, the package provides a convenient alternative. Video frames are stored as blobs at database file .db which can be read as quickly as the .JPEG files but without the additional large memory requirements.

---

Package requirements

The two required packages are opencv for image/frame loading and numpy for array manipulation. Make sure that both are installed before running any functions.

Multiprocessing: The code uses multiprocessing for improving speeds, thus the total time required for the conversion varies across different processors. The code has been tested on an AMD Threadripper 2950X with an average conversion time of 48 minutes for ~500K videos.

---

Dataset structure

The package assumes a fixed dataset structure such as:

<dataset>    
  │
  └──<class 1>
  │     │
  │     │─── <video_data_1.mp4>
  │     │─── <video_data_2.mp4>
  │     │─── ...
  │    ...      
  │
  └───<class 2>
  │      │
  │      │─── <video_data_1.mp4>
  │      │─── <video_data_2.mp4>
  │      │─── ...
 ...    ...

---

Usage

The main code is at the jpgs2single.py file. To run the convertor simply call the convert function with the base directory of the dataset and the destination directory for where to save the generated databases.

from dataset2database import convert
#or
from jpgs2singlefile import convert

convert(my_dataset_dir, my_target_dir)

---

Frames.db files

Video frames are stored in frames.db files with their video name and frame number as their ObjID and the frames array are stored as blobs. The name format is basically <video_name>/frame _ [frame number in 5-digit format]

File viewer: If you want to ensure that everything has been converted correctly, you can use SQLiteStudio which provides an easy to use multi-platform interface (available for Windows, Mac and Ubuntu).

---

Database loading

Loading the database can easily be done with an SQL SELECT command based on a list of all frames with specified ObjIds. Then, with the help of np.fromstring() and cv2.imdecode() functions the images can be again converted to uint8 arrays.

An example of data loading in python can be found below:

import sqlite3
import cv2
import numpy as np

con = sqlite3.connect('my_video_database.db')
cur = con.cursor()


# retrieve entire video from database (frames are unordered)
frame_names = ["{}/{}".format(my_path.split('/')[-1],'frame_%05d'%(index+1)) for index in frame_indices]
sql = "SELECT Objid, frames FROM Images WHERE ObjId IN ({seq})".format(seq=','.join(['?']*len(frame_names)))
row = cur.execute(sql,frame_names)

ids = []
frames = []
i = 0

row = row.fetchall()
# Video order re-arangement
for ObjId, item in row:
  #--- Decode blob
  nparr  = np.fromstring(item, np.uint8)
  img = cv2.imdecode(nparr, cv2.IMREAD_COLOR)
  ids.append(ObjId)
  frames.append(img)
  i+=1

# Ensuring correct order of frames
frames = [frame for _, frame in sorted(zip(ids,frames), key=lambda pair: pair[0])]

# (if required) array conversion [frames x height x width x channels]
frames = np.asarray(frames)

cur.close()
con.close()

---

Installation through git

Please make sure, Git is installed in your machine:

$ sudo apt-get update
$ sudo apt-get install git
$ git clone https://github.com/alexandrosstergiou/dataset2database.git

---

Installation through pip

The latest stable release is also available for download through pip

$ pip install dataset2databse

Version history

11 April 2020 : Version 0.1 - bug fixes for convert() function.

6 April 2020 : Initial code created.