Let's break down why your watermark isn't fitting correctly and fix it step by step.

First, let's look at your original command—there are a couple of potential issues here:

1. Ambiguous variable references: Using W/H and w/h works in simple cases, but it's unclear which stream's dimensions you're targeting. Using explicit labels like main_w/main_h (for your video) and overlay_w/overlay_h (for your watermark) avoids confusion.
2. Parameter order: The -preset flag is an encoder option, so it should come after your filter complex and before the output file path.
3. Unaccounted video rotation: Most mobile-recorded videos have rotation metadata (e.g., 90 degrees for portrait mode). FFmpeg doesn't auto-apply this rotation by default, so your W/H calculations are using the raw video resolution, not the actual displayed resolution.
4. Missing encoder specification: Without explicitly setting -c:v libx264, FFmpeg might fall back to a default encoder that doesn't play nicely with your filter setup.

Solution 1: Basic Centered Watermark (No Rotation Issues) #

If your video doesn't have rotation metadata, fix the command order and use explicit variables:

String[] complexCommand = {
    "-i", AppUtils.videoPath,
    "-i", framelocalPath,
    "-filter_complex", "overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2",
    "-preset", "ultrafast",
    "-c:v", "libx264",
    dest1.getAbsolutePath()
};

Solution 2: Handle Rotation + Scale Watermark to Fit Video #

If your video has rotation (or you want the watermark to scale proportionally with the video), use this enhanced command:

String[] complexCommand = {
    "-i", AppUtils.videoPath,
    "-i", framelocalPath,
    "-filter_complex",
    // Auto-fix video rotation first to match displayed dimensions
    "[0:v]rotate=auto[main_video]; " +
    // Scale watermark to 20% of video height (adjust 0.2 to your needs), preserve aspect ratio
    "[1:v][main_video]scale2ref=w=oh*mdar:h=ih*0.2[scaled_watermark][main_video]; " +
    // Center the scaled watermark on the fixed video
    "[main_video][scaled_watermark]overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2",
    "-preset", "ultrafast",
    "-c:v", "libx264",
    dest1.getAbsolutePath()
};

Key Explanations: #

• rotate=auto: Automatically applies the video's rotation metadata, so your width/height calculations match how the video is actually displayed.
• scale2ref=w=oh*mdar:h=ih*0.2: Scales the watermark to 20% of the video's height while preserving its original aspect ratio. Change 0.2 to adjust the size (e.g., 0.15 for 15% height).
• Explicit variable names (main_w, overlay_w): Eliminates any ambiguity about which stream's dimensions you're referencing.

Quick Debug Steps: #

1. Check if your video has rotation metadata:
   Run this command in your terminal:

   ffprobe -v error -show_entries stream_tags=rotate -of default=noprint_wrappers=1:nokey=1 /path/to/your/video.mp4
   

   If it returns a number like 90 or 270, rotation is likely the main issue.
2. Verify your watermark's dimensions:

   ffprobe -v error -show_entries stream=width,height -of default=noprint_wrappers=1:nokey=1 /path/to/your/watermark.png
   

   If the watermark is larger than the video, scaling it down (like in Solution 2) is essential.

内容的提问来源于stack exchange，提问作者Harsh Joshi