Applications


How to create a video from thousands of images using ffmpeg

We have this simulation that creates several frames demonstrating the life-cycle of an ant colony.
Having thousands of pictures is not very useful most of the times so we decided to create a video out of those frames.
To do so, we decided to use ffmpeg. The names of the files that we generate are 5 digit zero-leading auto increment numbers (e.g 00001.png and 00002.png) so we ended up with the following command:

ffmpeg -framerate 60 -i %05d.png video.mp4;


How to create a video from an audio file and an image using ffmpeg

Recently, we had this audio file ( mp3) that we wanted to upload to youtube.com. As it is known, youtube does not allow uploading audio files. Taking that into consideration we had to create a video with a static image just to upload the audio file to youtube. To do that, we used ffmpeg and the following command:

ffmpeg -loop 1 -i Saturday.png -i 20181020.mp3 -shortest -acodec copy 20181020.mp4;


How we concatenate multiple mp3 files into one using ffmpeg

Recently, we needed to concatenate multiple mp3 files into one. We had at our disposal a machine that had ffmpeg installed.
To perform the merge, we created a list (separated by the character |) of the mp3 files, in the order we wanted them merged and executed the concat operation of ffmpeg to complete our task. Our resulting command was the following

ffmpeg -i "concat:20181021_080743.MP3|20181021_090745.MP3|20181021_100745.MP3" -acodec copy 20181021.mp3


LibreOffice Calc: Get workbook path only

Get workbook path only

For Linux and Mac

=LEFT(
  CELL("filename"),
  FIND(
    CHAR(1),
    SUBSTITUTE(
      CELL("filename"),
      "/",
      CHAR(1),
      LEN(CELL("filename")) - LEN(
        SUBSTITUTE(
          CELL("filename"),
          "/",
          ""
        )
      )
    )
  ) -1
)&"'"

For Windows

=LEFT(
  CELL("filename"),
  FIND(
    CHAR(1),
    SUBSTITUTE(
      CELL("filename"),
      "\",
      CHAR(1),
      LEN(CELL("filename")) - LEN(
        SUBSTITUTE(
          CELL("filename"),
          "\",
          ""
        )
      )
    )
  ) -1
)&"'"

Bonus

If you want to remove the ' characters as well that are around the filename and path use the following  solution, this will allow you to create hyperlinks for the folders as well

=REPLACE(
  LEFT(
    CELL("filename"),
    FIND(CHAR(1),
      SUBSTITUTE(
        CELL("filename"),
        "/",
        CHAR(1),
        LEN(CELL("filename")) - LEN(
          SUBSTITUTE(
            CELL("filename"),
            "/",
            ""
          )
        )
      )
    ) -1
  )
  ,1,1,""
)

To create hyperlink as well, use the following

=HYPERLINK(
  REPLACE(
    LEFT(
      CELL("filename"),
      FIND(CHAR(1),
        SUBSTITUTE(
          CELL("filename"),
          "/",
          CHAR(1),
          LEN(CELL("filename")) - LEN(
            SUBSTITUTE(
              CELL("filename"),
              "/",
              ""
            )
          )
        )
      ) -1
    )
    ,1,1,""
  )
)

 

 


LibreOffice Calc: Get workbook full path with filename

Get workbook full path with filename

=LEFT(CELL("filename"),FIND("#",CELL("filename"))-1)

Explanation

If you want to get the workbook filename and path, you can do so with a formula that uses the LEFT and the FIND function.

The CELL("filename") function is used to get the full file name and path along with current sheet link:

The result will look like this:

'file:///home/user/path/documentName.ods'#$sheetName

Using the FIND function we find the position of the delimiter # and then using the LEFT function, we extract just the full directory path with the filename. We know the number of characters to extract by locating the the position of the hash # character with FIND and then subtracting 1 (to exclude itself as well).

Extra

If you want to remove the ' characters as well that are around the filename and path use the following solution

=REPLACE(
  LEFT(
    CELL("filename"),
    FIND(
      "#",
      CELL("filename")
    )-2
  ), 1, 1,""
)

 


LibreOffice Calc: Get workbook filename only

Get workbook filename only

For Linux and Mac

=TRIM(
  RIGHT(
    SUBSTITUTE(
      LEFT(
        CELL("filename"),
        FIND("#", CELL("filename")) -2
      ),
      "/",
      REPT(" ", LEN(CELL("filename")))
    ),
  LEN(CELL("filename"))
  )
)

For Windows

=TRIM(
  RIGHT(
    SUBSTITUTE(
      LEFT(
        CELL("filename"),
        FIND("#", CELL("filename")) -2
      ),
      "\",
      REPT(" ", LEN(CELL("filename")))
    ),
  LEN(CELL("filename"))
  )
)

The only change is changing the delimiter from / to \.


Horrible Solution: How to delete all docker logs

Recently, we needed to delete the logs of a running docker setup. To do so, we used the following horrible solution:

First, we executed docker system info | grep "Docker Root Dir";to get the installation path of docker. It resulted to the following:

Docker Root Dir: /var/lib/docker

Then, we truncated all log files using the following command while executing as root:

truncate -s 0 /var/lib/docker/containers/*/*-json.log;

Bonus

To make the command a onliner, use the following:

sudo sh -c 'truncate -s 0 $(docker system info | grep "Docker Root Dir" | cut -d ":" -f2 | cut -d " " -f2-)/containers/*/*-json.log';


Notes on how to connect from an external machine to a docker database in Google Compute Engine

A) Create a firewall rule in your VPC Network that allows you to connect to your database from outside the network: https://console.cloud.google.com/networking/firewalls/list

B) From your remote machine repair your database using mysqlcheck.

On Fedora you can install it by installing the MariaDB package as follows:

sudo dnf install mariadb -y;

The following command will automatically repair all databases and tables in that instance of MySQL, where of course the user has access:

mysqlcheck --host 45.37.15.225 --port 33061 --user admin --all-databases --auto-repair --password;

C) Edit the new firewall rule and either disable it or delete it for security.


Easy way to repair and optimize core WordPress MySql DataBase Tables

To manually repair and optimize the core WordPress tables of your MySql (or MariaDB) database:

A) edit your wp-config.php and add

define('WP_ALLOW_REPAIR', true);

right before the line

/* That's all, stop editing! Happy blogging. */

B) Visit the following link (and replace example.com with the domain or the IP of your site installation)

https://example.com/wp-admin/maint/repair.php

C) Press the Repair and Optimize Database button and wait for some time (depending on the size of the core tables of your installation)

D) Once the above step is done, remove or comment out (by adding a # at the beginning of the line) the line:

define('WP_ALLOW_REPAIR', true);

You need to do this step to to prevent this page (which could potentially take a lot of resources) from being used by unauthorized users.