CatVideo Concatenator

CatVideo Concatenator is a simple Android app written in Kotlin that allows users to select multiple videos from their device and concatenate them into a single video without transcoding. The app displays real-time text-based progress, preserves the original video orientation, and saves the output video to the device's camera roll.

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If you like this app, you can support me via Ko-fi. 💜💜💜

Features

• Select multiple videos from the device storage.
• Concatenate videos without re-encoding (fast and preserves original quality).
• Display progress updates: percentage complete, free space remaining, and estimated time left.
• Corrects video orientation so the output is not upside-down.
• Screen rotation is disabled during processing to prevent crashes.
• Optionally, users can support the developer via a clickable Ko-fi link in the app.

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How It Works

1. The app lets the user select one or more videos from their device.
2. Videos are processed on a background thread using Android's MediaExtractor and MediaMuxer.
3. The app concatenates the video and audio tracks sequentially, adjusting timestamps to ensure smooth playback.
4. Progress is reported in real-time to a TextView, including:
   • Completion percentage
   • Free space on the device
   • Estimated time remaining
5. The final concatenated video is saved in the device's Movies directory and is visible in the camera roll.

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Basic Instructions

1. Tap the “Select Videos” button.
2. Choose multiple video files from your device.
3. The app will display concatenation progress in real-time.
4. Once complete, the output video is saved to your camera roll.

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Use Cases

• Combine clips from an event into a single video.
• Merge multiple short recordings into one file for sharing.
• Quickly compile video highlights without quality loss.
• Export HDR videos without a HDR editing program

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Caveats & Notes

• The app does not transcode; all videos must have compatible codecs (e.g., H.264 video and AAC audio). Mixing incompatible formats may cause errors.
• The app assumes all videos have the same rotation. If videos have different orientations, some clips may appear sideways.
• Screen rotation is locked during processing to avoid crashes.
• The app only handles videos accessible via the system document picker (does not scan all internal storage automatically).
• Large files may take time depending on device performance and storage speed.
• Free space is reported in MB; ensure enough storage is available for the combined video.

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Development Notes

• Written in Kotlin for Android using MediaExtractor and MediaMuxer.
• Background processing is done using a simple Thread.
• Output files are saved in Movies via MediaStore for immediate visibility in gallery apps.
• Progress is reported to the main thread using runOnUiThread.