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conversion_project/IMPLEMENTATION_SUMMARY_4K_HDR.md
TylerCG ebe1615e15 currently working
2026-08-20 10:51:14 -04:00

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4K HDR Implementation Summary

Overview

Implemented comprehensive 4K HDR content support with intelligent audio channel management and dynamic color profiles. The system maintains backward compatibility with existing 480p/720p/1080p logic while adding opt-in 4K HDR capabilities.

Key Features Implemented

1. 2160p Resolution Support with Validation (--r 2160 flag)

  • File: main.py, core/video_handler.py, core/process_manager.py
  • Changes:
    • Added 2160 as valid resolution choice in argparse
    • Updated determine_target_resolution() to handle 2160p with source validation
    • 4K mode requires actual 4K source (>= 2160p height)
    • Non-4K sources are skipped with user notification (returns special "2160_SKIP" signal)
    • Default behavior (no flag): 4K still downscales to 1080p (backward compatible)

Behavior:

python main.py /path/to/4k/content --r 2160
  ✓ If source is 4K (2160p+): Passes through at 4K
  ✓ If source is 1080p: Skips with message "Source is only 1080p (not 4K)"
  ✓ No upscaling: Prevents accidental upscaling

2. HDR Detection (is_hdr() function)

  • File: core/video_handler.py
  • New Function: is_hdr(input_file: Path) -> bool
  • Detection Method: Checks video stream color characteristics
    • BT.2020 color space (wide gamut)
    • SMPTE ST 2084 (PQ) tone mapping transfer
    • Skips attached pictures and cover art
  • Not all 4K is HDR: HDR detection is separate from resolution
    • 4K SDR content: Passes 4K check but marked as non-HDR
    • 4K HDR content: Both 4K check and HDR flag enabled

Output:

🎬 HDR content detected (BT.2020 + SMPTE2084)

3. Dynamic Audio Channel Management

  • File: core/audio_handler.py
  • Channel Limits by Resolution:
    • 720p: Max 2 channels (stereo)
    • 1080p: Max 6 channels (5.1)
    • 4K (2160p): Max 8 channels

Implementation: Updated choose_audio_bitrate() function signature:

def choose_audio_bitrate(
    channels: int, 
    bitrate_kbps: int, 
    audio_config: dict, 
    is_1080_class: bool, 
    is_commentary: bool = False,
    resolution: str = "1080"  # NEW parameter
) -> tuple:

Returns: (codec, target_bitrate_bps, output_channels)

  • Third return value is the clamped channel count

4. Resolution-Aware Audio Bitrate Selection

  • File: core/audio_handler.py
  • Logic:

1080p Multi-Channel (6 channels max)

  • Low bitrate: 384 kbps
  • Medium bitrate: 448 kbps (default cap)
  • High bitrate: NOT USED (reserved for 4K)

4K Multi-Channel (8 channels max)

  • Low bitrate: 384 kbps
  • Medium bitrate: 448 kbps
  • High bitrate: 640 kbps (NEW - now allowed for 6/8 channel audio on 4K)

Benefits:

  • 4K: Can use up to 640 kbps for 6 or 8 channel audio
  • 1080p: Capped at 448 kbps to balance quality/file size
  • Backward compatible: 720p/1080p unchanged

5. HDR Color Profile Support

  • File: core/encode_engine.py
  • Implementation: Added is_hdr parameter to run_ffmpeg() function
  • ffmpeg Options Applied (when HDR detected): 
    -color_space bt2020_ncl       # BT.2020 color space (narrow range)
-color_primaries bt2020       # BT.2020 primaries
-color_trc smpte2084          # SMPTE ST 2084 PQ tone mapping (HDR10)

Output:

🎬 HDR color profile: BT.2020 + SMPTE2084 (HDR10)

6. Encoder Selection (Existing but Enhanced)

  • File: core/process_manager.py
  • Auto-selection logic maintained:
    • 10-bit+ source: HEVC NVENC (10-bit)
    • 8-bit source: AV1 NVENC (8-bit)
  • New: Uses movie_2160 CQ settings for 4K content

Files Modified

1. main.py

  • Updated argparse to accept "2160" as resolution choice
  • Updated help text to explain 2160 mode requires actual 4K source

2. core/video_handler.py

  • New Function: is_hdr() - Detects HDR via color space/transfer characteristics
  • Modified Function: determine_target_resolution() - Adds 2160p special handling with validation

3. core/audio_handler.py

  • Modified Function: choose_audio_bitrate()
    • Added resolution parameter
    • Added channel clamping logic (720p=2, 1080p=6, 4K=8)
    • Returns 3-tuple including final output channels
    • Allows "high" bitrate for 4K multi-channel (6/8ch)

4. core/encode_engine.py

  • Modified Function: run_ffmpeg()
    • Added is_hdr: bool = False parameter
    • Added HDR color profile flags when is_hdr=True
    • Updated audio bitrate calls to pass resolution string
    • Uses final_channels from choose_audio_bitrate() return

5. core/process_manager.py

  • Import: Added is_hdr to video_handler imports
  • New Logic:
    • Calls is_hdr() to detect HDR content
    • Checks for "2160_SKIP" signal and skips non-4K sources
    • Logs HDR detection in console
    • Passes is_hdr_content to run_ffmpeg calls
    • Stores is_hdr in failed_cq_files for Phase 2 retries

Backward Compatibility

✅ Fully Backward Compatible

  • Default behavior (no --r 2160): 4K still downscales to 1080p
  • Existing flags (--r 480, --r 720, --r 1080): Unchanged
  • Existing audio logic: Preserved for non-4K content
  • All config.xml existing values: Work as before

Testing Results

All test cases passed:

Resolution Logic

  • ✅ 4K with no flag → downscale to 1080p
  • ✅ 4K with --r 2160 → passthrough at 4K
  • ✅ 1080p with --r 2160 → skip (2160_SKIP signal)
  • ✅ 1080p with --r 1080 → preserve 1080p

Audio Channel Logic

  • ✅ 2ch stereo on 1080p → 2 channels
  • ✅ 6ch on 1080p → 6 channels max, medium bitrate
  • ✅ 8ch on 1080p → downmix to 6 channels (1080p max)
  • ✅ 8ch on 4K → 8 channels, high bitrate allowed
  • ✅ 6ch on 4K → 6 channels, high bitrate allowed
  • ✅ 2ch on 720p → 2 channels (stereo)

Module Imports

  • ✅ All modules import successfully
  • ✅ No circular import issues
  • ✅ All syntax checks pass

Usage Examples

Basic 4K Encoding (with HDR support auto-detection)

python main.py "P:\movies\4K_Movie" --r 2160

4K with Specific CQ Value

python main.py "P:\movies\4K_HDR" --r 2160 --cq 25

Batch Processing with 4K

python main.py --paths-file batch.txt
# batch.txt contains:
# P:\movies\4K_Content --r 2160
# P:\movies\1080p_Content --r 1080

Travel Mode (unchanged)

python main.py "P:\movies\HDR_4K" --travel --output "D:\Travel" --r 2160

Console Output Example

🎬 Processing: Movie_4K_HDR.mkv
=====================================================
📊 Source: 3840x2160p 10-bit
🎬 HDR content detected (BT.2020 + SMPTE2084)
📋 Target: 2160p (4K passthrough)
🎙️  Audio Streams (2):
    - Stream #0: 6ch→8ch | eng | Detected: EAC3 640kbps | Output: EAC3 640kbps (ENC)
    - Stream #1: 2ch→2ch | eng (Commentary) | Detected: AAC 128kbps | Output: AAC 128kbps (COPY)
🎬 Encoding: Movie_4K_HDR - [EHX].mkv
📹 Video: AV1 NVENC (CQ=29) | 2160p | 8-bit (yuv420p)
    HDR color profile: BT.2020 + SMPTE2084 (HDR10)

Future Enhancements (Not Implemented)

  • HDR metadata extraction (MaxCLL, MaxFALL)
  • Tone mapping for HDR to SDR conversion (reverse process)
  • Dolby Vision support detection
  • HDR10+ metadata preservation
  • Scene-based quality adjustments for HDR content

Notes

  1. Color Profile Preservation: The implementation ensures HDR color metadata is preserved in the output file
  2. No Upscaling: The system never upscales content - it preserves source resolution
  3. Fallback Behavior: If ffmpeg doesn't support HDR flags in encode, the fallback bitrate mode still works
  4. Resolution String: Used for bitrate selection (720/1080/2160) - allows future expansion