NDI monitor for Android

A minimal, standalone NDI® receiver for Android based on the NewTek/Vizrt NDI SDK (v6.3.2.0). It detects NDI sources on the network (mDNS), displays video with audio, and allows manual connection using IP[:port].

Architecture

app/
├── src/main/
│   ├── AndroidManifest.xml
│   ├── jniLibs/{arm64-v8a,armeabi-v7a,x86,x86_64}/libndi.so   ← NDI SDK
│   ├── cpp/
│   │   ├── CMakeLists.txt
│   │   ├── ndi_jni.cpp                           ← native JNI bridge (+ I420/YV12/NV12)
│   │   └── ndi/Processing.NDI.*.h                ← NDI headers
│   └── java/com/lekozaur/ndiviewer/
│       ├── DecodeStatus.kt / SourceProbe.kt      ← classification + HX vs Full NDI probe
│       ├── NdiNative.kt   (JNI surface: NdiFinderJni, NdiReceiverJni, NdiNative)
│       ├── NdiFinder.kt   (discovery thread: wait_for_sources + get_current_sources)
│       ├── NdiStream.kt   (video + statistics threads + JNI orchestration)
│       ├── VideoRenderer.kt (FitSurfaceView, double-buffered bitmap, aspect-fit)
│       ├── SourceAdapter.kt (RecyclerView + green/yellow/red status dot)
│       ├── LocaleHelper.kt (PL/EN/DE/ES/IT/FR)
│       └── MainActivity.kt (UI: top sheet, left vertical bar, LIVE red chip)

Data Flow

NDI Sender ──TCP/UDP (mDNS)──► NDI SDK (libndi.so)
                                   │
                                   ▼  NdiReceiverJni.capture (video thread)
                    copy/convert: RGBA/BGRX/BGRA/UYVY → RGBA  (BT.709 limited)
                                   │  (DirectByteBuffer, zero-copy within JNI boundaries)
                                   ▼
                            Renderer.onFrame (video thread)
                          Bitmap.copyPixelsFromBuffer (2x ping-pong)
                                   │
                                   ▼  Choreographer ~120 Hz (UI thread)
                            FitSurfaceView → drawBitmap aspect-fit
                                   ▲
                                   │
                          Audio (native audio thread)
                          capture_v2 audio → SPSC ring → AAudio stream (PCM float)

Key Decisions

• Forced color format: we receive using NDIlib_recv_color_format_RGBX_RGBA — the SDK itself performs the down-conversion from UYVY/4:2:2 to RGBA. This maps directly to Bitmap.Config.ARGB_8888 (RGBA in memory, BE→LE).
• Fallback conversion: if the source sends UYVY despite the preference (e.g. in fastest mode), the wrapper performs UYVY→RGBA (BT.709 limited, 4:2:2) in C++.
• Zero allocations in the hot path: the wrapper maintains two global DirectByteBuffer instances sized stride*height and switches the index for each frame. In Java, two Bitmap instances (ping-pong) receive copyPixelsFromBuffer — with no GC overhead.
• Threads: native video + audio run on two separate threads (NDIlib_recv_capture_v2 supports simultaneous calls from multiple threads — this is guaranteed by the SDK). Statistics run on a third thread every 1 second.
• Audio: AAudio low-latency, PCM float format, downmixes more than 2 channels to stereo (NDI typically provides 2/8/16 channels). The AAudio stream is restarted when the format changes (rare). Muting is controlled using an atomic bool.
• Power-saving mode: BANDWIDTH_LOWEST=0 reduces resolution and compression (useful over Wi-Fi), while BANDWIDTH_HIGHEST=100 provides full quality.
• Aspect ratio: FitSurfaceView calculates onMeasure based on picture_aspect_ratio (or xres/yres) and maintains letterboxing both vertically and horizontally.
• Discoverability: mDNS requires a MulticastLock — acquired when the BottomSheetDialog is opened and released when it is closed.
• Lifecycle: the Activity's configChanges keeps the orientation without restarting. singleTask prevents multiple instances.

Build Configuration

Element	Value
Gradle	8.11.1 (cached)
AGP	8.7.3
Kotlin	2.1.21
NDK	27.1.12297006
CMake (Android)	3.22.1
compileSdk	35
minSdk	26 (required by AAudio)
targetSdk	35
JDK	17
ABIs	arm64-v8a, armeabi-v7a, x86, x86_64
NDI SDK	v6.3.2.0

Building

cd D:\lekozaur\ndiviewer
gradlew.bat --no-daemon assembleDebug

Output: app/build/outputs/apk/debug/app-debug.apk.

Replace JDK 17 in gradle.properties (org.gradle.java.home) with the correct directory if yours is different.

Decode Status Indicator (v0.5)

The source list displays a colored dot on the right-hand side of the name:

Color	Meaning	FourCC
🟢 Green	Will definitely decode — full Full NDI, uncompressed (UYVY, UYVA, RGBA/BGRA + I420/YV12/NV12) is natively supported in ndi_jni.cpp (uyvyToRgba/i420ToRgba/… → RGBA).
🟡 Yellow	May work — unknown format or no frame received during the 2.7 s probe (e.g. P216/PA16 16-bit, or timeout). Worth trying.
🔴 Red	Will definitely not work — compressed `NDI	HX / H.264/H.265/SpeedHQ (H264/H265/AVC1/HEVC/SHQ0-7`). Requires a hardware decoder that does not exist on this device. Switch the sender to Full NDI (NDI Screen Capture → Full NDI, OBS NDI → Main profile).

Pre-probe heuristic: a name containing HX, H264, H265, SpeedHQ, HEVC, or AVC is immediately marked 🔴. Otherwise, every new entry is probed in the background by SourceProbe (creates a temporary NdiReceiverJni, connects for ~900 ms ×3, classifies FourCC via DecodeClassifier, and updates SourceAdapter through updateStatus).

Visual Helpers - BETA (branch visual-helpers / NDI-discovery)

BETA - experimental features, may lower FPS on 4K. Branch visual-helpers is not merged into main.

• False Color (VideoRenderer.falseColorEnabled, btnFalseColor in left bar): heatmap via FalseColorTable (IRE 0..108 from falsecolor.json: 0 White #FFFFFF -> 2 Blue #020346 -> 10 Light Blue #2496FF -> 20 Dark Grey #52524F -> 42 Bright Purple #FE1BFE -> 48 Medium Gray -> 52 Green -> 58 Light Grey -> 78 Dark Yellow -> 84 Yellow -> 94 Orange -> 100 Red #DE0E0D, maps luma 16->0 IRE, 235->100 IRE). Scale FalseColorScaleView 33dp with 29sp right-justified numbers, draggable. Toggle, icon alpha 1.0/0.5. Histogram removed in v0.8.0 per request.

Build from branch:

git checkout visual-helpers
gradlew.bat --no-daemon assembleDebug

NDI Discovery Server — removed (Play policy)

The background discovery server (NdiDiscoveryService / NdiDiscoveryServer, BETA on branch NDI-discovery) was removed from main in v1.0.1: keeping mDNS warm in the background requires a dataSync foreground service, which Google Play only allows for user-initiated data transfers. Source discovery works while the app is open (source list → NdiFinder + MulticastLock), with no background service and no extra permissions.

Limitations / TODO

• H.264/NDI-HX in 🔴 mode requires an external decoder (MediaCodec H264 or libavcodec) — currently it is detected and reported as Video decoder not found (FourCC=H264 ...) instead of showing a black screen. For I420/YV12/NV12 (a common HX decoder fallback when available), BT.709 conversion has already been added.
• libndi.so from SDK v6.3.2 does not have 16-KB page alignment — Google Play has required this for new apps since November 2025. This requires rebuilding the SDK from source or upgrading the NDI SDK.
• Audio may require minor tuning for a specific device (NDI typically uses 48 kHz, and the default AAudio path is also 48 kHz on Android).
• Video/audio synchronization in the first version is based on displaying frames as quickly as they arrive (as-fast-as-possible). For demanding broadcast applications, using NDIlib_FrameSync instead of raw recv_capture is recommended.

NDI License

The application embeds libndi.so from the official NDI SDK package (EULA NDI SDK License Agreement.pdf). Production use requires acceptance of the Vizrt NDI license terms.

Trademarks, Copyright and NDI SDK Notice

NDI® is a registered trademark of Vizrt NDI AB and is used under applicable license terms.

This application uses the NDI® SDK provided by Vizrt (formerly NewTek). The NDI SDK, including libndi.so and the associated header files, is proprietary software owned by Vizrt and/or its licensors and is subject to the NDI SDK License Agreement.

This project is not affiliated with, endorsed by, sponsored by, or otherwise officially associated with Vizrt or NewTek.

All trademarks, service marks, product names, logos, and company names mentioned in this project are the property of their respective owners.

Copyright © 2026 the authors of NDI monitor for Android - and Opencode :).

The source code of this application is distributed under the license specified in this repository. This license does not grant any rights to redistribute, modify, or otherwise use the NDI SDK beyond the rights expressly granted by the applicable NDI SDK License Agreement.

For commercial or production distribution, ensure that your use and distribution of the NDI SDK comply with the current licensing terms provided by Vizrt.