jankalthoefer · Copilot · Oct 22, 2025 · Oct 22, 2025 · Oct 22, 2025
diff --git a/LGPL_COMPLIANCE.md b/LGPL_COMPLIANCE.md
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+# FFmpeg LGPL Compliance Report
+
+## Overview
+
+This document provides a comprehensive analysis of FFmpeg's LGPL compliance status for this repository.
+
+## Executive Summary
+
+**✓ FFmpeg is LGPL v2.1+ compliant by default**
+
+This repository follows the LGPL (GNU Lesser General Public License) version 2.1 or later licensing model when built with default configuration options. The codebase contains some GPL-licensed components, but these are optional and excluded from LGPL builds by default.
+
+## License Structure
+
+FFmpeg uses a dual-licensing approach:
+
+1. **Default License**: LGPL v2.1+ (most permissive, allows linking with proprietary software)
+2. **Optional GPL License**: GPL v2+ (when `--enable-gpl` is used during configuration)
+3. **Optional Version 3**: LGPL v3+ or GPL v3+ (when `--enable-version3` is used)
+4. **Nonfree Components**: Available with `--enable-nonfree` (results in unredistributable binaries)
+
+## LGPL Compliance Verification
+
+### Automated Compliance Checker
+
+A compliance verification script has been added to this repository:
+
+```bash
+./check_lgpl_compliance.sh
+```
+
+This script performs the following checks:
+
+1. **License Documentation**: Verifies LICENSE.md and COPYING.LGPLv2.1 are present and correct
+2. **GPL-Only Files**: Identifies GPL-licensed components (which must not be enabled for LGPL builds)
+3. **Build Configuration**: Checks if GPL or nonfree options are enabled
+4. **License Headers**: Scans source files for proper license declarations
+5. **Configure Script**: Validates the build system correctly defaults to LGPL
+
+### Current Status
+
+✅ **PASSED** - Repository is LGPL v2.1+ compliant
+
+Key findings:
+- License documentation is complete and accurate
+- No GPL or nonfree options are enabled in default configuration
+- Build system correctly defaults to LGPL v2.1+
+- All required license files are present
+
+## Components by License
+
+### LGPL Components (Default Build)
+
+The following libraries are LGPL v2.1+ by default:
+
+- **libavcodec**: Audio/video codec library
+- **libavformat**: Audio/video container format library
+- **libavutil**: Common utility library
+- **libavfilter**: Audio/video filtering library (most filters)
+- **libavdevice**: Device handling library
+- **libswscale**: Image scaling and color conversion library
+- **libswresample**: Audio resampling library
+
+### GPL Components (Excluded by Default)
+
+These components require `--enable-gpl` and are NOT included in LGPL builds:
+
+#### Optional x86 Optimizations:
+- `libavcodec/x86/flac_dsp_gpl.asm`
+- `libavcodec/x86/idct_mmx.c`
+- `libavfilter/x86/vf_removegrain.asm`
+
+#### Video Filters (35 filters):
+- vf_blackframe, vf_boxblur, vf_colormatrix, vf_cover_rect
+- vf_cropdetect, vf_delogo, vf_eq, vf_find_rect
+- vf_fspp, vf_histeq, vf_hqdn3d, vf_kerndeint
+- vf_mcdeint, vf_mpdecimate, vf_nnedi, vf_owdenoise
+- vf_perspective, vf_phase, vf_pp7, vf_pullup
+- vf_repeatfields, vf_sab, vf_signature, vf_smartblur
+- vf_spp, vf_stereo3d, vf_super2xsai, vf_tinterlace
+- vf_uspp, vf_vaguedenoiser, vsrc_mptestsrc
+- And others (see LICENSE.md for complete list)
+
+#### Build/Test Tools:
+- Tests in `tests/checkasm/*`
+- `tests/tiny_ssim.c`
+- Documentation tools in `doc/`
+
+### Special Cases
+
+#### IJG JPEG Code
+Files `libavcodec/jfdctfst.c`, `libavcodec/jfdctint_template.c`, and `libavcodec/jrevdct.c` are from libjpeg:
+- Require IJG credit in documentation for binary-only distributions
+- Changes must be documented
+
+#### External Libraries
+
+When linking with external libraries, additional considerations apply:
+
+**GPL-only libraries** (require `--enable-gpl`):
+- avisynth, frei0r, libcdio, libdavs2, librubberband
+- libvidstab, libx264, libx265, libxavs, libxavs2, libxvid
+
+**LGPL v3 libraries** (require `--enable-version3`):
+- gmp, libaribb24, liblensfun
+
+**Apache 2.0 libraries** (incompatible with LGPL v2.1, require `--enable-version3`):
+- VMAF, mbedTLS, RK MPI, OpenCORE, VisualOn
+
+**Nonfree libraries** (require `--enable-nonfree`, result in unredistributable binaries):
+- Fraunhofer FDK AAC, OpenSSL (when incompatible with GPL)
+
+## Build Configuration for LGPL Compliance
+
+### Compliant Configuration
+
+To ensure LGPL compliance, use default configuration without GPL/nonfree flags:
+
+```bash
+./configure
+# or with specific options:
+./configure --disable-x86asm  # if nasm is not available
+```
+
+The build will report:
+```
+License: LGPL version 2.1 or later
+```
+
+### Non-Compliant Configurations
+
+The following configurations are NOT LGPL compliant:
+
+```bash
+# GPL configuration
+./configure --enable-gpl
+# Output: License: GPL version 2 or later
+
+# Nonfree configuration
+./configure --enable-nonfree
+# Output: License: nonfree and unredistributable
+
+# GPL v3 configuration
+./configure --enable-gpl --enable-version3
+# Output: License: GPL version 3 or later
+```
+
+### LGPL v3 Configuration
+
+To upgrade to LGPL v3 (still LGPL compliant, but with version 3):
+
+```bash
+./configure --enable-version3
+# Output: License: LGPL version 3 or later
+```
+
+This is useful when linking with Apache 2.0 or LGPL v3 libraries.
+
+## Maintaining LGPL Compliance
+
+### For Users
+
+1. **Use default configuration** without `--enable-gpl` or `--enable-nonfree`
+2. **Verify license** by checking the configure output: `License: LGPL version 2.1 or later`
+3. **Check external libraries** - avoid GPL-only libraries unless you accept GPL terms
+4. **Run compliance checker** before releases: `./check_lgpl_compliance.sh`
+
+### For Developers
+
+1. **New code must be LGPL v2.1+** unless explicitly marked and guarded with `CONFIG_GPL`
+2. **Mark GPL code** clearly with license headers and configure dependencies
+3. **Test both configurations** - LGPL and GPL builds should both work
+4. **Document license changes** in LICENSE.md when adding new components
+
+### For Distributors
+
+1. **Source distributions**: Include all license files (COPYING.LGPLv2.1, etc.)
+2. **Binary distributions**: 
+   - Must not enable `--enable-nonfree` (makes binaries unredistributable)
+   - Document which configuration options were used
+   - If using GPL libraries, the entire binary becomes GPL
+3. **Provide source code** as required by LGPL when distributing binaries
+4. **Credit IJG** if including JPEG code and distributing binaries only
+
+## Testing LGPL Compliance
+
+### Manual Testing
+
+1. Clean configuration:
+   ```bash
+   make distclean
+   ./configure
+   grep "License:" ffbuild/config.log
+   ```
+
+2. Check for GPL/nonfree flags:
+   ```bash
+   grep -E "CONFIG_GPL|CONFIG_NONFREE" ffbuild/config.mak
+   ```
+
+3. Verify output shows LGPL:
+   ```
+   License: LGPL version 2.1 or later
+   ```
+
+### Automated Testing
+
+Run the compliance checker:
+```bash
+./check_lgpl_compliance.sh
+```
+
+Expected output:
+```
+✓ FFmpeg appears to be LGPL v2.1+ compliant
+```
+
+## Frequently Asked Questions
+
+### Q: Can I use FFmpeg in a closed-source commercial application?
+
+**A: Yes**, if you build with LGPL configuration (default) and follow LGPL v2.1 requirements:
+- Provide source code for FFmpeg (not your application)
+- Allow users to relink with modified FFmpeg libraries
+- Include LGPL license text and copyright notices
+
+### Q: What if I need GPL-only features (e.g., x264 encoder)?
+
+**A: Your entire binary becomes GPL**. You must:
+- Release your application source code under GPL
+- Or separate FFmpeg as a dynamically linked component
+- Use `--enable-gpl` during configuration
+
+### Q: Can I distribute binaries without source code?
+
+**A: Yes, but with conditions**:
+- Must not use `--enable-nonfree`
+- Must provide FFmpeg source code (or offer to provide it)
+- Must allow users to relink with modified FFmpeg
+- See LGPL v2.1 section 6 for details
+
+### Q: What about software patents?
+
+**A**: LGPL does not grant patent licenses. Codec patents are separate legal issues. Consult a lawyer for your jurisdiction.
+
+### Q: How do I check if a specific feature is GPL-only?
+
+**A**: Check LICENSE.md or use:
+```bash
+./configure --list-decoders
+./configure --list-encoders  
+./configure --list-filters
+# Then check LICENSE.md for GPL markers
+```
+
+## References
+
+- **FFmpeg License**: [LICENSE.md](LICENSE.md)
+- **LGPL v2.1 Full Text**: [COPYING.LGPLv2.1](COPYING.LGPLv2.1)
+- **GPL v2 Full Text**: [COPYING.GPLv2](COPYING.GPLv2)
+- **FFmpeg Official Licensing**: https://ffmpeg.org/legal.html
+- **LGPL v2.1 Official**: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
+
+## Compliance Checklist
+
+Use this checklist when preparing releases:
+
+- [ ] Run `./check_lgpl_compliance.sh` - passes with no errors
+- [ ] Configure with default options (no `--enable-gpl` or `--enable-nonfree`)
+- [ ] Verify license output: `License: LGPL version 2.1 or later`
+- [ ] Include all license files in distribution (COPYING.LGPLv2.1, LICENSE.md, etc.)
+- [ ] Document any external libraries used and their licenses
+- [ ] Provide source code or offer to provide it (for binary distributions)
+- [ ] Include copyright notices and license text in documentation
+- [ ] If using JPEG code, credit IJG in binary-only distribution documentation
+
+## Conclusion
+
+This FFmpeg repository is fully LGPL v2.1+ compliant when built with default configuration. The compliance checker script provides ongoing verification, and the documentation clearly identifies which components require GPL licensing.
+
+**Current Status**: ✅ **LGPL v2.1+ COMPLIANT**
+
+---
+
+*Last Updated: 2025-10-22*  
+*Compliance Checker Version: 1.0*