Color Grading - grading video footage

Rule #1: the preview IS the final result

The user already APPROVED the color in the web UI based on a preview generated from the canonical filter chains in apps/server/src/color.ts (GRADE_PRESETS). When applying it to the real video you MUST use that exact filter chain

• do not invent your own, do not "improve it further". A different chain = a color that no longer matches what the user picked.

Source of truth for presets + manual adjustments

Read apps/server/src/color.ts:

• GRADE_PRESETS - 14 color templates (tu-nhien, tuoi-sang, vivid, cinematic, teal-orange, film-vintage, mau-phim, golden-hour, am, lanh, dem-xanh, moody, pastel, den-trang) with their -vf chains.
• GradeAdjust - the user's manual tweaks stacked ON TOP of the preset (brightness/contrast/ saturation/gamma via eq, colortemperature, vibrance); the buildFilterChain(preset, tonemap, adjust) function assembles them in the correct order: tonemap -> preset -> manual adjustments.
• The edit prompt already prints the complete -vf chain for each asset - JUST USE IT VERBATIM.

Delog / HDR tonemap (insert BEFORE the preset)

Inspect the footage with ffprobe:

ffprobe -v error -select_streams v:0 -show_entries stream=color_transfer,color_primaries -of csv=p=0 input.mp4

If color_transfer is arib-std-b67 (HLG - iPhone/Android HDR capture) or smpte2084 (HDR10), or color_primaries is bt2020 -> insert the tonemap BEFORE the preset:

zscale=t=linear:npl=100,tonemap=hable:desat=0,zscale=p=bt709:t=bt709:m=bt709:r=tv,format=yuv420p

Professional camera log (S-Log3, D-Log, V-Log...) whose metadata does not declare HDR needs the vendor's .cube LUT - if that LUT is not in the system, tell the user instead of guessing.

Workflow for grading one video

1. Probe the color (command above) -> decide whether a tonemap is needed.
2. Produce the graded version (high quality encode, audio untouched):

ffmpeg -y -i assets/source.mp4 -vf "<tonemap-if-needed>,<preset-chain>" -c:v libx264 -crf 16 -preset medium -c:a copy assets/source.graded.mp4

3. Visual verification (mandatory): extract 3 frames (start / middle / end) of the graded version and LOOK at each one: are skin tones natural and not blown out orange? are highlights not clipped? are blacks not crushed? If something is wrong -> report back, do NOT silently change the filter (the user locked in the preset).
4. Use the .graded.mp4 version throughout the ENTIRE pipeline instead of the original (meta.json srcVideo; transcription can use either file since the audio is copied unchanged).
5. Record in the asset description (assets.json) which preset was used to grade it, so it does not get graded twice later.

Known issues

• Grading twice: the .graded.mp4 gets the preset applied again in a later session -> harsh color. ALWAYS check the filename and assets.json before grading.
• Grading only the main video and forgetting b-roll/inserted images: inserted images usually do not need grading (they are graphics), but b-roll shot on the same camera needs the same preset - check the asset descriptions to know which files came from the camera.
• Missing format=yuv420p at the end of the tonemap chain -> the output is 10-bit and HyperFrames/browsers may not play it.