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JohannesItten ca682eaf0a Initial commit: testpattern → fakesink pipeline over MXL shared memory

- NodeBase, Signal, FlowDef, V210 shared headers
- testpattern node: SMPTE 75% color bars writer at 25fps
- fakesink node: non-blocking MXL reader with per-second stats
- studio-manager: FlowGraph data model, graph-driven fork/exec launcher
- mxl pinned as submodule at 0ae1dc5

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

2026-06-23 13:35:01 +03:00

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DMF Studio — AI Context

Read ARCHITECTURE.md first for the full picture. This file adds guidance specific to working in this codebase.

Project in one sentence

Node-based media signal processing system: each node is a separate C++ process, nodes exchange video/audio via MXL shared memory, studio-manager orchestrates them, Vue.js frontend planned.

Current state

Core built: testpattern node (color bars writer), fakesink node (reader/logger), studio-manager (fork/exec orchestrator)
Not built yet: real processing nodes, Vue frontend, graph.json persistence, WebSocket API

Key conventions

Node configuration comes from NODE_CONFIG env var (JSON). Never hardcode flow UUIDs.
MXL domain comes from MXL_DOMAIN env var. Default: /dev/shm/dmf-studio (Linux) or /tmp/dmf-studio (macOS).
All shared utilities live in shared/ as header-only files. New nodes add a subdirectory under nodes/.
Timing always goes through MXL time API (mxlGetCurrentIndex, mxlGetNsUntilIndex, mxlSleepForNs). Do not use std::chrono::system_clock for frame timing — MXL uses TAI.
V210 line stride comes from configInfo.discrete.sliceSizes[0] after mxlCreateFlowWriter. Never hardcode 5120.

What the user cares about

Dmitry is not a very experienced C++ developer. Prefer architectural discussion before implementation.
Keep code minimal and clear. No premature abstractions.
When adding a new node type, follow the patterns in nodes/testpattern/main.cpp and nodes/fakesink/main.cpp.

MXL API quick reference

mxlCreateInstance(domain, nullptr)
mxlCreateFlowWriter(inst, flow_def_json, nullptr, &writer, &configInfo, &created)
mxlCreateFlowReader(inst, flow_id, nullptr, &reader)
mxlFlowWriterOpenGrain(writer, index, &grain, &buf)
mxlFlowWriterCommitGrain(writer, &grain)
mxlFlowReaderGetGrain(reader, index, timeout_ns, &grain, &buf)
mxlGetCurrentIndex(&rate)
mxlGetNsUntilIndex(next_index, &rate)  → ns to sleep
mxlSleepForNs(ns)
mxlIsFlowActive(inst, flow_id, &active)
mxlFlowSynchronizationGroup — for multi-input nodes (PiP)

MXL error codes to handle in readers

MXL_STATUS_OK — grain ready
MXL_ERR_TIMEOUT — writer stalled, log and retry same index
MXL_ERR_OUT_OF_RANGE_TOO_LATE — fell behind ring buffer, call mxlGetCurrentIndex and jump

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