refactor: modular architecture with multi-algorithm bitrate control and config file

[andrescera]

Summary

Major refactoring of belacoder to introduce modular architecture, pluggable bitrate control algorithms, and INI config file support.

Changes

Project Structure Reorganization

• All source files moved to src/ - Clean root directory
• Updated Makefile for new structure
• Updated .gitignore for src/*.o

Multi-Algorithm Bitrate Control (Closes #3)

• balancer.h - Generic BalancerAlgorithm interface with init/step/cleanup
• balancer_registry.c - Algorithm lookup by name
• balancer_adaptive.c - Default algorithm (RTT + buffer-based)
• balancer_fixed.c - Constant bitrate, no adaptation
• balancer_aimd.c - TCP-style Additive Increase Multiplicative Decrease

Select algorithm at runtime:

./belacoder -a adaptive pipeline.txt host 4000  # Default
./belacoder -a fixed pipeline.txt host 4000
./belacoder -a aimd pipeline.txt host 4000

Configuration File Support

• config.h/c - INI config file parser
• belacoder.conf.example - Documented example config
• -c CLI flag - Load config from file
• SIGHUP - Reload config at runtime

[general]
min_bitrate = 500    # Kbps (500 Kbps)
max_bitrate = 6000   # Kbps (6 Mbps)
balancer = adaptive

[srt]
latency = 2000       # ms

[adaptive]
incr_step = 30       # Kbps increase step
decr_step = 100      # Kbps decrease step

[aimd]
incr_step = 50       # Kbps
decr_mult = 0.75     # Reduce to 75% on congestion

Algorithm Tuning Wired Up

• All algorithm-specific config values now actually affect behavior
• Adaptive: incr_step, decr_step, incr_interval, decr_interval
• AIMD: incr_step, decr_mult, incr_interval, decr_interval

Bitrate Module Extraction (Part of #2)

• bitrate_control.h/c - Adaptive algorithm internals
• Pure logic, no GStreamer dependency
• BitrateContext struct encapsulates all state
• Testable in isolation

Packet Loss Detection

• Added packet loss as congestion signal
• Triggers fast decrease when loss detected

Documentation Updates

• docs/architecture.md - Updated with new structure, modules
• docs/bitrate-control.md - Multi-algorithm docs, updated API

New File Structure

belacoder/
├── src/
│   ├── belacoder.c           # Main application
│   ├── config.c/h            # Config file parser
│   ├── balancer.h            # Algorithm interface
│   ├── balancer_adaptive.c   # Default algorithm
│   ├── balancer_fixed.c      # Fixed bitrate
│   ├── balancer_aimd.c       # AIMD algorithm
│   ├── balancer_registry.c   # Algorithm lookup
│   └── bitrate_control.c/h   # Adaptive internals
├── pipeline/
├── docs/
├── Makefile
├── belacoder.conf.example
└── README.md

Verification

• ✅ make clean && make - Builds with zero warnings
• ✅ ./belacoder -v - Returns version
• ✅ All three algorithms selectable via -a
• ✅ Config file loads and applies correctly
• ✅ SIGHUP reloads config at runtime
• ✅ Documentation updated

Related Issues

• Closes Multi-Algorithm Bitrate Control Support #3 (Multi-Algorithm Bitrate Control Support)
• Part of Future Improvements: Code Structure and Testing #2 (Code Structure and Testing - module extraction complete)