Post-Processing videos

Step 3.1: Identify Start and End Times

• Open your raw video file in a media player (e.g., VLC).

• Note the start time (start_time) and end time (end_time) of the segment you want to keep. Example: If you want to keep a clip from 00:01:15 to 00:03:45:

  • start_time = 00:01:15 (1 minute 15 seconds)

  • end_time = 00:03:45 (3 minutes 45 seconds)

Step 3.2: Use FFmpeg to Cut the Video

Run the following command to cut the video:

ffmpeg -i input.mp4 -ss 00:01:15 -to 00:03:45 -c copy cut_output.mkv

• -i input.mp4: Specifies the input video file.

• -ss 00:01:15: Skips to the start time (75 seconds).

• -to 00:03:45: Stops at the end time (225 seconds).

• -c copy: Copies the video and audio streams without re-encoding, preserving the original quality.

• cut_output.mkv: The output file name.

Step 3.3: Verify the Cut

• Play the trimmed video (cut_output.mkv) in a media player to ensure it starts and ends where intended.

Step 4.1: Organize Your Assets

Before starting Kdenlive, ensure all your assets are ready: - Trimmed Video Clips: Outputs from Step 3 (e.g., cut_output.mkv). - Audio Files: Background music, sound effects, or voiceovers. - Graphics and Titles: Logos, overlays, or text elements for branding. - Transitions: Pre-made transitions (if needed) or use Kdenlive’s built-in effects.

Place all these files in a dedicated folder (e.g., kdenlive_assets) for easy access.

Step 4.2: Set Up the Kdenlive Project

1. Create a New Project:

   • Open Kdenlive and go to File > New Project.

   • Choose a profile that matches your video resolution and frame rate (e.g., 1080p 30fps).

2. Import Media:

   • Drag and drop your trimmed video clips, audio files, and graphics into the Project Bin (left panel in Kdenlive).

3. Set the Timeline Layout:

   • Use multiple tracks for better organization:

     • Track 1: Main video clips.

     • Track 2: Titles, overlays, or graphics.

     • Track 3: Background music or sound effects.

     • Track 4: Transitions or additional effects.

Step 4.3: Assemble the Mini-Videos

1. Add Video Clips to the Timeline:

   • Drag your trimmed video clips onto Track 1 and arrange them in the desired order.

2. Add Titles and Text:

   • Go to the Titles and Text section in the toolbar.

   • Create eye-catching titles for each mini-video. Use bold fonts, animations, and colors that match your branding. Place the titles on Track 2 above the video clips.

3. Incorporate Graphics and Overlays:

   • Add logos, lower-thirds, or decorative overlays to enhance the visuals. Use keyframes to animate these elements for a dynamic effect.

4. Add Background Music:

   • Drag a background music file onto Track 3. Adjust the volume using Volume Keyframes to ensure it doesn’t overpower the main audio (e.g., voiceover or dialogue).

5. Apply Transitions:

   • Use Kdenlive’s built-in transitions (e.g., fade, slide, or dissolve) between clips for smooth visual flow. Alternatively, import custom transitions if you have them.

6. Enhance Audio:

   • Use the Audio Effects tab to improve clarity:

     • Add compression for consistent volume levels.

     • Apply equalization (EQ) to enhance specific frequencies.

     • If needed, record a voiceover using Kdenlive’s Record Monitor feature.

Step 5.1: Run ffprobe on cut_output.mkv

Open your terminal or command prompt and run:

ffprobe -i cut_output.mkv

This will display detailed information about the video file, including: - Video codec: Check if it’s already H.264 (libx264). - Resolution: Note the width and height (e.g., 1920x1080). - Frame rate: Verify the frame rate (e.g., 30 fps). - Audio codec: Check if it’s AAC or another codec.

For more granular details, use:

ffprobe -i cut_output.mkv -show_streams

Option 1: Add the Profile in Kdenlive

1. Open Kdenlive and go to Settings > Configure Kdenlive > Environment > FFmpeg Export Settings [[1]].

2. Add a new custom profile with the following details:

   • Profile Name: OBS Export

   • Parameters:

   • Extension: .mkv

3. Save the profile.

Option 2: Create an MLT XML Profile

<?xml version="1.0"?>
<profile>
    <name>OBS Export</name>
    <description>Custom profile for OBS-compatible video export</description>
    <extension>mkv</extension>
    <parameters>
        f=matroska
        vcodec=libx264
        preset=medium
        profile:v=high
        crf=23
        pix_fmt=yuv420p
        r=30
        vf=scale=trunc(iw/2)*2:trunc(ih/2)*2,setdar=16/9
        acodec=aac
        ab=128k
        ar=48000
        ac=2
    </parameters>
</profile>

Verify the Profile

• Restart Kdenlive if it’s already open.

• Go to File > Render. In the Rendering Profile dropdown, you should now see “OBS Export” listed.

Step 8.1: Run ffprobe

ffprobe -i final_output.mkv

Check: - Container: Should be Matroska (mkv). - Video codec: Should be H.264 (libx264). - Resolution and aspect ratio: Should match the scaling filter (16:9). - Audio codec: Should be AAC with stereo channels.

Step 8.2: Play the Video

Test the video in a media player like VLC to confirm smooth playback, proper audio sync, and correct resolution.

Step 9.1: Prepare the Files

Ensure both videos have the same resolution, frame rate, and codec settings.

Step 9.2: Create a Text File to List the Files

Create a text file (concat_list.txt) with the following format:

file 'mini_presentation.mkv'
file 'cut_output.mkv'

Step 9.3: Run the Concatenation Command

ffmpeg -f concat -safe 0 -i concat_list.txt -c copy final_concatenated.mkv

Step 9.4: Verify the Concatenated Video

Test the final video using ffprobe and a media player.

Step 10.1: Probe the Length of the Mini-Presentation Video

To determine the duration of the mini-presentation video (mini_presentation.mkv), use ffprobe. The output will provide the exact length of the video in seconds.

Run the following command in your terminal or command prompt:

ffprobe -i mini_presentation.mkv -show_entries format=duration -v quiet -of csv="p=0"

• -i mini_presentation.mkv: Specifies the input file.

• -show_entries format=duration: Extracts the duration of the video.

• -v quiet: Suppresses unnecessary logging.

• -of csv="p=0": Outputs only the duration value.

Example Output: If the mini-presentation video is 17.5 seconds long, the output will be:

17.500000

This value (e.g., 17.5) represents the duration of the mini-presentation video in seconds. You’ll use this value in the next step to adjust the audio volume.

Step 10.2: Use the Duration in the FFmpeg Command

The duration of the mini-presentation video determines where the volume adjustment begins. Specifically, the start parameter in the FFmpeg command should match the duration of the mini-presentation video.

Here’s the updated FFmpeg command with placeholders for clarity:

ffmpeg -i final_concatenated.mkv -filter_complex \
"[0:a]atrim=end=<DURATION>,asetpts=PTS-STARTPTS[a_before]; \
 [0:a]atrim=start=<DURATION>,asetpts=PTS-STARTPTS,volume=3.0[a_trimmed]; \
 [a_before][a_trimmed]concat=n=2:v=0:a=1[aout]" \
-map 0:v -map "[aout]" -c:v copy output_with_adjusted_volume.mkv

Replace <DURATION> with the actual duration of the mini-presentation video (e.g., 17.5).

Example Command:

If the mini-presentation video is 17.5 seconds long, the command becomes:

ffmpeg -i final_concatenated.mkv -filter_complex \
"[0:a]atrim=end=17.5,asetpts=PTS-STARTPTS[a_before]; \
 [0:a]atrim=start=17.5,asetpts=PTS-STARTPTS,volume=3.0[a_trimmed]; \
 [a_before][a_trimmed]concat=n=2:v=0:a=1[aout]" \
-map 0:v -map "[aout]" -c:v copy output_with_adjusted_volume.mkv

• end=17.5: Specifies the end time for the first audio segment (the mini-presentation part).

• start=17.5: Specifies the start time for the second audio segment (the part after the mini-presentation).

• volume=3.0: Increases the volume of the second audio segment by a factor of 3.0.

Step 10.3: Verify the Final Output

After running the command, test the resulting video (output_with_adjusted_volume.mkv) to ensure the audio transitions smoothly and the volume adjustment starts at the correct point.

1. Play the Video: Use a media player like VLC to confirm:

   • The audio remains unchanged during the mini-presentation (first 17.5 seconds).

   • The audio volume increases after the mini-presentation ends.

2. Check Audio Sync: Ensure the audio is properly synchronized with the video throughout the entire duration.

Summary Here’s what we’ve accomplished in this step:

1. Used ffprobe to determine the duration of the mini-presentation video (e.g., 17.5 seconds).

2. Updated the FFmpeg command to split the audio into two parts:

   • The first part (up to 17.5 seconds) remains unchanged.

   • The second part (after 17.5 seconds) has its volume increased.

3. Verified the final output to ensure smooth transitions and balanced audio levels.

The resulting file, output_with_adjusted_volume.mkv, now has consistent audio levels and is ready for further processing or publishing.

Key Notes

• The duration of the mini-presentation video is critical for ensuring the volume adjustment starts at the correct point.

• Always verify the duration using ffprobe to avoid manual errors.

• Adjust the volume parameter (e.g., 3.0) as needed to achieve the desired audio level.

Step 10.2: Play the Video

Test the video in a media player to confirm smooth transitions and balanced audio levels.

Step 11.1: Run the Command

ffmpeg -i output_with_adjusted_volume.mkv -c:v libx264 -preset medium -crf 23 -c:a aac -b:a 192k -movflags +faststart output_youtube.mp4

Step 11.2: Verify the Output

Test the video in a media player and upload it to YouTube.