This document discusses improvements made to a wearable camera system used by law enforcement to address issues with video recording reliability. The key points are: 1. The previous camera architecture (Camera 1) was inflexible and its APIs were no longer supported in newer Android versions, so a new architecture (Camera 2) was implemented using a pipeline approach. 2. Under the old system, any failure during video recording like a pulled battery would corrupt the MP4 file since metadata was only written at the end, making the file unplayable. 3. To solve this, the solution was to "make the MP4 streamable" by changing how video data was written so that the file would remain

1. No More Video Loss
Alex Rivkin

2. The camera doesn’t lie.
I think the video and the millions of people who
saw it, certainly put pressure on the
prosecutors to take some actions
Geoffrey Phillip Alpert - Professor of criminology

3. Agenda
• Android wearable camera requirements
• Video architecture camera 2
• Android video layers
• Our solution for keeping recorded process safe in abnormal situation

4. Wearable Camera
● Based on Android N
● Removable battery for
10 hours
● Increased storage - 64
GB
● Camera resolution FHD
● Small display for
recorded video preview
● Continuous video cashing
of last 30 seconds
● Automatic contextual
activation of video recording
based on sensors.
● Uploading video files to
backend at end of shift

5. Old architecture Camera 1
● Designed as a black box
● Three operating modes:
1. Preview
2. Video Record
3. Still Capture
● Hard to implement new features
● API of camera 1 are not supported after Android 7

6. New architecture Camera 2
● Camera subsystem as a pipeline
● Converts each capture request into one image captured by the camera
sensor
● A request contains all desired capture settings and the list of output
surfaces to push image buffers into for this request

7. setRepeatingRequest()
API Camera 2

8. SurfaceTexture
Android Video Layers
Application
Camera
Device
Camera
Manager
Capture
Session
Camera
Service
Camera
Provider
Camera3Device
Video HAL Hardware
Composer
SurfaceView
Surface
MediaCodec
Surface
MediaMuxer
MPEG4WriterSurfaceFlinger
SurfaceTexture
EglSurface
AudioRecord
AudioFlinger
Audio HAL
Media Framework
OpenMax-based MMF
V4L2 driver
Stagefright
ALSA
MIC SPKRDISPLAYCamera VFE/CPP CODEC
FrameBuffer
Driver
V4L2 driver
Circle queue
Control flow
Raw video
YUV:4.2.0
Raw audio
PCM 16000
Encoded video
H264
Encoded audio
audio/mp4
Preview
ISP

9. Video Recording Problem
● Android OS writes metadata of MP4 file only at end of recording
● Any failure during video recording like battery pull out will cause to MP4 file
corruption.
● The file will be not playable.

11. Solution ….. make mp4 streamable !!!!
Before change After change

12. THANK YOU
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