Rewind and Resolve: A deep dive into building Session Replay for Android
summary
Builds a session replay that captures 1 FPS screenshots, masks sensitive text per line using view layout and compose semantics, and stitches 5‑second segments into MP4 via MediaCodec/MediaMuxer. Uses PixelCopy (API 26) plus Curtains to get the current Window, saves JPEGs at quality 80, and downscales to reduce work; derives image color by drawing into a single‑pixel bitmap. Handles Compose by reading the compose semantics tree, fixes a 16×16 block size video bug, and saves ~35–40% main‑thread time.
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chapters (15)
- 0:00Sentry and Session Replay
- 3:38What is Session Replay
- 5:47Building Session Replay
- 6:52Replay video algorithm
- 8:17Efficient screenshots with Pixel Copy
- 13:12Masking sensitive data
- 22:03Masking Jetpack Compose
- 32:54Storing screenshots
- 33:57Video segments from screenshots
- 37:50Video encoding challenges
- 40:21Reducing replay overhead
- 42:28Optimizing view traversal
- 44:35Hybrid SDK support
- 45:20Future plans
- 46:21Q&A
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