README

PhotoPrism — FFmpeg Integration

Last Updated: November 22, 2025

Overview

internal/ffmpeg wraps the ffmpeg CLI to transcode videos to AVC/H.264, remux containers, and extract preview frames in a predictable, testable way. Command builders share option structs so CLI tools, workers, and tests can select software or hardware encoders without duplicating flag logic.

Constraints

• Relies on the system ffmpeg binary; defaults to FFmpegBin but callers may override Options.Bin.
• Inputs are internal filenames and option structs (not user input); exec invocations are annotated with #nosec G204.
• Downstream jobs may run concurrently, so TranscodeCmd returns a useMutex hint to serialize expensive work.
• Remux and extract commands honor Force and reuse shared map flags; metadata copying is limited to safe defaults.

Goals

• Provide consistent command lines for software and hardware AVC encoders.
• Keep remuxing and preview extraction lightweight while preserving metadata where possible.
• Centralize quality and size clamping logic so UIs/CLI can pass user preferences safely.

Non-Goals

• Full coverage of every FFmpeg codec or container; the package focuses on MP4/H.264 paths required by PhotoPrism.
• Direct management of FFmpeg installation or GPU availability.

Encoders, Containers, & Hardware

• Software AVC: encode.TranscodeToAvcCmd (x264 or default encoder).
• Intel Quick Sync: internal/ffmpeg/intel (h264_qsv) with optional Options.Device.
• NVIDIA NVENC: internal/ffmpeg/nvidia (h264_nvenc).
• Apple VideoToolbox: internal/ffmpeg/apple (h264_videotoolbox).
• VA-API: internal/ffmpeg/vaapi (h264_vaapi) supporting optional device paths.
• V4L2 M2M: internal/ffmpeg/v4l (h264_v4l2m2m) for ARM/embedded targets.
• Containers: MP4 is the primary target (fs.VideoMp4); RemuxCmd can handle other fs.Type values when provided.
• Streaming flags: encode.MovFlags defaults to use_metadata_tags+faststart to keep outputs stream-friendly.

Package Layout (Code Map)

• encode/ — shared option structs, quality helpers, default map/metadata flags, software AVC command builder.
• apple/, intel/, nvidia/, vaapi/, v4l/ — hardware-specific AVC command builders.
• remux.go — container-only transfers with metadata copy and temp-file safety.
• transcode_cmd.go — selects encoder, handles animated image inputs, and signals mutex usage.
• extract_image_cmd.go — JPEG/PNG preview frame extraction with color-space presets.
• test.go & *_test.go — reusable command runner and smoke tests (use fixtures in testdata/).
• ffmpeg.go — package logger hook.

Related Packages & Entry Points

• internal/thumb calls these builders for video previews and thumbnails.
• internal/commands and workers select encoders based on configuration options and reuse encode.Options.
• pkg/fs supplies path helpers, existence checks, and file-mode constants referenced by remux/extract logic.

Configuration & Safety Notes

• Clamp size and quality via NewVideoOptions to [1, 15360] pixels and the defined quality bounds.
• Remuxing respects Options.Force; without it existing outputs are preserved.
• Metadata copying uses -map_metadata and clean sanitizers; only safe string fields (title, description, comment, author, creation_time) are added when set.
• Hardware helpers expect the matching FFmpeg build and devices; callers should gate selection via config or environment (see PHOTOPRISM_FFMPEG_ENCODER guidance in AGENTS.md).

Testing

• Run unit tests: go test ./internal/ffmpeg/...
• Hardware-specific tests assume the encoder is available; keep runs gated via config when adding new cases.

Operational Tips

• Prefer TranscodeCmd over manual exec.Command to keep logging, metadata, and mutex hints consistent.
• Use RemuxFile to convert containers without re-encoding; it creates a temp file and swaps atomically.
• For preview frames, pass encode.Options with SeekOffset and TimeOffset computed from video duration (see NewPreviewImageOptions).