How to crop a video on Ubuntu?

ffmpeg -i input.mp4 -vf "crop=1200:626:279:89" -c:v libx264 -crf 20 -c:a copy output.mp4


To crop a video on Ubuntu, you use FFmpeg’s crop filter. Cropping is different from resizing; it’s like taking a pair of scissors to the video frame to cut out a specific area (like removing a watermark or focusing on a specific person).

The logic for cropping is: crop=width:height:x:y

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1. The Basic Crop Command

If you know the exact dimensions you want to keep, use this:

Bash

ffmpeg -i input.mp4 -vf "crop=1280:720:0:0" -c:a copy output_cropped.mp4

• 1280: The width of the "box" you want to keep.

• 720: The height of the "box" you want to keep.

• 0: The X coordinate (distance from the left edge) where the box starts.

• 0: The Y coordinate (distance from the top edge) where the box starts.

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2. Common "Real World" Examples

To crop a square from the center (great for social media):

Bash

ffmpeg -i input.mp4 -vf "crop=ih:ih" -c:a copy output_square.mp4

(Note: ih stands for "Input Height." This tells FFmpeg to make the width equal to the height.)

To cut the video in half (keep only the right side):

Bash

ffmpeg -i input.mp4 -vf "crop=iw/2:ih:iw/2:0" -c:a copy output_right_half.mp4

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3. How to find your coordinates (The Easy Way)

Trying to guess "X" and "Y" coordinates in a terminal is hard. Here is a trick to do it visually:

1. Open your video in VLC.

2. Go to Tools > Effects and Filters.

3. Go to Video Effects > Crop.

4. Type in numbers until the video looks exactly how you want it.

5. Write down those numbers (Left, Right, Top, Bottom) and use them in this FFmpeg command:

Bash

# If you found: Left=100, Top=50, Width=800, Height=600
ffmpeg -i input.mp4 -vf "crop=800:600:100:50" -c:a copy output_cropped.mp4

---

Important Tips:

• Re-encoding: Because you are changing the actual picture, FFmpeg has to re-encode the video. I didn't include quality flags above to keep it simple, but for the best result, add -crf 20: ffmpeg -i input.mp4 -vf "crop=w:h:x:y" -c:v libx264 -crf 20 -c:a copy output.mp4

• Even Numbers: Just like before, H.264 (MP4) loves even numbers. If you get an error, make sure your width and height are divisible by 2.

How to convert a .webm video into a .mp4 one?

ffmpeg -i output_trimmed.webm -c:v libx264 -crf 23 -preset medium -c:a aac output.mp4

How to trim a video on Ubuntu?

ffmpeg -i toAi.webm -ss 02:42 -to 05:59 -c:v libvpx -crf 10 -b:v 1M -c:a libvorbis output_trimmed.webm

How to move all the files in a directory to another directory on Linux

Gemini, I used the command -

$ ls -alhSp | grep -v /

, and got a list of files in the current directory.

What command can I use to move the files in the above list to another directory, please?

That is a very specific (and clever) command! You're using ls to list all files, sorting them by size (-S), adding a trailing slash to directories (-p), and then using grep to filter out anything with a slash.

Essentially, you've isolated just the regular files in your current folder, ranked from largest to smallest.

To move that specific list to another directory, you have a few options depending on how "clean" you want the process to be.

---

Method 1: The "Xargs" Approach (Recommended)

This is the most efficient way to take the output of one command and pipe it into another. We use the -I flag to create a placeholder (often {}) for the filenames.

Bash

ls -alhSp | grep -v / | awk '{print $9}' | xargs -I {} mv {} /path/to/destination/

• awk '{print $9}': This is necessary because your original command uses -l (long format). awk grabs just the filename (the 9th column) so mv doesn't try to move the file permissions or timestamps.

• xargs -I {}: This tells the system: "Take each filename and put it where the {} is in the next command."

Method 2: The Simple "Wildcard" (If you don't need the sort order)

If your goal is simply to move all files but no folders and you don't actually care about the size sorting from your original command, a simple loop is often safer:

Bash

for file in *; do [ -f "$file" ] && mv "$file" /path/to/destination/; done

---

⚠️ A Note on File Names

If any of your files have spaces in their names, the ls | grep method can get messy. When dealing with complex file movements, using find is generally the "Gold Standard" because it handles hidden characters and spaces much better:

Bash

find . -maxdepth 1 -type f -exec mv {} /path/to/destination/ \;

• -maxdepth 1: Prevents it from looking into subfolders.

• -type f: Ensures only files are moved (ignoring directories).

---

Which one should you use?

If you want...	Use...
To keep using your ls logic	Method 1 (with awk)
The safest/fastest way	The find command
To avoid complex syntax	Method 2 (The loop)

Would you like me to explain how to modify that command to only move files over a certain size?

Yes, please. Thank you.

 

 

Since you are already using ls -S (sort by size), we can refine your pipeline to filter for specific size thresholds.

To do this effectively, we’ll swap ls for the find command. While ls is great for looking at files, find is a powerhouse for filtering them by attributes like size, age, or type.

---

Using find for Specific Sizes

This is the most reliable method. You can specify "greater than" (+) or "less than" (-) a certain size.

To move files larger than 100MB:

Bash

find . -maxdepth 1 -type f -size +100M -exec mv {} /path/to/destination/ \;

To move files smaller than 50KB:

Bash

find . -maxdepth 1 -type f -size -50k -exec mv {} /path/to/destination/ \;

Breakdown of the logic:

• .: Look in the current directory.

• -maxdepth 1: Don't go digging into subfolders.

• -type f: Only look for files (this replaces your grep -v / logic).

• -size +100M: The filter. Use k for Kilobytes, M for Megabytes, or G for Gigabytes.

• -exec mv {} ...: The "action" part that moves every file found.

---

The "Quick & Dirty" Way (Using your original command)

If you prefer to stick to your ls command and just want to "eyeball" it, you can use head to move only the top $X$ largest files.

To move the top 5 largest files:

Bash

ls -pS | grep -v / | head -n 5 | xargs -I {} mv {} /path/to/destination/

Note: This version removes the -alh flags. When piping to mv, we don't want the "human-readable" sizes or permissions (like 1.2G or -rw-r--r--) included in the text, otherwise mv will get confused and think those are the filenames!

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Comparison of Size Units

When using the -size flag in find, keep these suffixes in mind:

Suffix	Meaning	Example
k	Kilobytes	-size +50k (Over 50 KB)
M	Megabytes	-size +10M (Over 10 MB)
G	Gigabytes	-size +1G (Over 1 GB)
c	Bytes	-size +100c (Over 100 Bytes)

Would you like me to show you how to do a "dry run" first, so you can see exactly which files will be moved before actually moving them?

 Yes, please. Thank you.

 

Performing a dry run is a pro move. It allows you to verify your logic without actually changing any files—saving you from that "oh no" moment when you accidentally move the wrong thing.

The simplest way to do a dry run is to replace the mv command with echo. This will print the command to your terminal instead of executing it.

---

1. Dry Run with the find Command

This is the safest way to test your size filters.

Bash

find . -maxdepth 1 -type f -size +100M -exec echo "Moving:" {} \;

• What happens: The terminal will list every file larger than 100MB preceded by the word "Moving:". It won't actually move anything.

2. Dry Run with your ls Pipeline

If you are using the pipe method with xargs, just put echo before mv.

Bash

ls -pS | grep -v / | head -n 5 | xargs -I {} echo mv {} /path/to/destination/

• What happens: You will see a list of commands like mv file1.zip /dest/. If the paths look correct, you can just hit the "Up" arrow on your keyboard and remove the echo to run it for real.

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Comparison of Workflows

Step	Action	Command Key
1. Identify	List and filter	find or ls | grep
2. Verify	The Dry Run	echo
3. Execute	Final Move	mv

A Quick Pro-Tip: The "Verbose" Flag

If you want to see the files moving while they are actually being moved (a middle ground between a dry run and flying blind), use the -v flag with mv:

Bash

mv -v source_file destination/
# Output: 'source_file' -> 'destination/source_file'

Would you like to know how to undo a move if you realize you sent files to the wrong folder?

 Yes, please. Thank you.

 

Moving files is instantaneous on the same disk, so there isn't a "Ctrl+Z" or "Undo" button in the terminal. However, you can effectively "reverse" the move by flipping the logic of your command.

Here are the best ways to handle an accidental move:

1. The "Reverse Move" (The Manual Fix)

If you just moved a specific group of files into a folder, the quickest way back is to go into that folder and move them back to the parent directory (represented by ..).

Bash

cd /path/to/destination/
mv * ../

• Warning: Only do this if the destination folder was empty before you moved your files into it. Otherwise, you'll end up moving the original contents of that folder back to your source directory too!

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2. The "By Time" Undo (The Precision Fix)

If you moved files into a folder that already had other files in it, you can use find to identify only the files that arrived in the last few minutes.

To move files out that arrived in the last 5 minutes:

Bash

find /path/to/destination/ -maxdepth 1 -type f -cmin -5 -exec mv {} ./ \;

• -cmin -5: Finds files whose status changed (moved) less than 5 minutes ago.

• ./: Moves them back to your current working directory.

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3. Preventing Accidents: The "Interactive" Flag

To prevent needing an "undo" in the future, you can use the -i (interactive) flag. This forces the terminal to ask for your permission before overwriting any files at the destination.

Bash

mv -i source_file destination/
# Terminal: overwrite destination/source_file? (y/n)

Best Practices Summary

Situation	Safety Strategy
Before moving	Use echo for a Dry Run.
During the move	Use mv -v (Verbose) to see what's happening.
Potential Overwrites	Use mv -n (No-clobber) to prevent overwriting existing files.
The "Undo"	Use find with -cmin to isolate recently moved files.

Would you like me to show you how to create an "alias" so you can run these complex size-filtering moves with a single short command in the future?

 

 

 

 

The list of all the format options of the gq command in vim?

In Vim, the

'formatoptions' setting controls how automatic text formatting is performed. It accepts a string of single-character flags, each enabling a specific behavior. You can view the current value in your Vim session with the command :set fo? or get a detailed explanation of all flags using the Vim help documentation via :help fo-table. 

The common and widely recognized formatoptions flags are:

• t: Auto-wrap text at the width specified by the 'textwidth' option.
• c: Auto-wrap comments at 'textwidth', automatically inserting the current comment leader character(s) (defined by 'comments' or 'commentstring').
• q: Allow formatting with the gq operator.
• r: Automatically insert the current comment leader after pressing <Enter> in Insert mode.
• o: Automatically insert the current comment leader after pressing o or O in Normal mode.
• n: Recognize numbered lists when formatting, using the pattern defined in 'formatlistpat'. This helps avoid joining list items into a single paragraph.
• b: Auto-wrap text (backwards) when a line grows longer than 'textwidth'. The line is broken at the last white space before 'textwidth'.
• v: Vi-compatible auto-wrapping (wraps at 'textwidth' in Insert mode).
• j: Delete comment characters when joining lines using the J command.
• l: Leave long lines as they are when entering Insert mode; only format if a line explicitly exceeds 'textwidth' due to typing.
• m: Join with a space between the joined lines if there isn't one already.
• p: Do not auto-wrap paste. When pasting text in Insert mode, do not apply auto-wrapping based on 'textwidth'.
• u: Undo separate; make an undo command revert one line at a time instead of the entire paragraph formatting operation.
• 2: Keep the indent of the second line when a paragraph is formatted (useful for some programming styles).
• 1: Do not break a line after a single character (e.g., prevent single-letter words from being alone on the next line). 
• a: Automatic formatting of paragraphs (changes are immediately reformatted). 

The default value is typically tcq. To add an option, you can use :set formatoptions+=<char>, and to remove one, use :set formatoptions-=<char>. 

Vim global command - how to apply 2 or more patterns?

:g/====\|----/-1p

Prints the line above all the lines with '====', and the line above all the lines with '----'

How to convert a PDF file into a Markdown file or HTML file?

To convert a PDF into a Markdown file using the Python-based tool called Marker on Ubuntu, you need to set up the environment, install the

marker-pdf package, and then use the command-line interface. 

Prerequisites

Before installing Marker, ensure your Ubuntu system meets the following prerequisites:

• Python: Version 3.10 or higher is required.
• PyTorch: Marker needs PyTorch to run, as it relies on deep learning models.
• System Libraries: You may need additional system libraries for advanced features like OCR with ocrmypdf or tesseract. 

Step-by-Step Guide

1. Open your terminal on Ubuntu.
2. Install system dependencies (optional, but recommended for full functionality, including OCR):
   bash

   # Install required apt packages
   sudo apt-get update
   sudo apt-get install -y build-essential libssl-dev libffi-dev python3-dev
   # Install tesseract and ghostscript related dependencies
   sudo apt-get install -y libleptonica-dev libtesseract-dev pkg-config
   sudo apt-get install -y ocrmypdf ghostscript
   

3. Create a virtual environment to avoid conflicts with other Python projects (recommended):
   bash

   python3 -m venv marker_env
   source marker_env/bin/activate
   

4. Install PyTorch by following the instructions on the official PyTorch website for your specific system configuration (CPU or GPU). A typical CPU-only installation command might look like:
   bash

   pip install torch torchvision torchaudio
   

5. Install Marker using pip. You can install the basic PDF package or the full version for other document types:
   bash

   # For PDF conversion only
   pip install marker-pdf
   
   # For full functionality (PDFs, images, etc.)
   # pip install 'marker-pdf[full]'
   

6. Convert a PDF file to Markdown using the command line tool marker_single.
   
   $ marker_single /path/to/file.pdf  
   
   --output_format [markdown|json|html|chunks]: Specify the format for the output results.
   --output_dir PATH: Directory where output files will be saved. Defaults to the value specified in settings.OUTPUT_DIR.
   
   https://github.com/datalab-to/marker