mlt-render

MLT Render

Headless render of an MLT-format timeline (Kdenlive's native format) using the melt CLI.

Procedure

1. Verify melt

command -v melt >/dev/null || { echo "melt not installed. Try: sudo apt install melt  (or sudo apt install mlt-tools on some distros)"; exit 1; }

2. Resolve inputs

Field	Default
Source	required: .kdenlive or .mlt file
Output	default: <project>/renders/<basename>_<timestamp>.mp4
Profile name	optional — load from render-profiles.json
Inline params	codec, bitrate (or qp), resolution, fps — only when no profile chosen

SRC="$(realpath "$INPUT")"
test -f "$SRC" || { echo "Not a file: $SRC"; exit 1; }
case "$SRC" in
  *.kdenlive|*.mlt) ;;
  *) echo "Not an MLT-format file: $SRC"; exit 1 ;;
esac

3. Build the melt command

melt renders via a consumer chain. Two modes:

3a. With a render profile — load codec/QP/resolution/fps from render-profiles.json (same shape used by render-with-profile). Build a melt avformat consumer:

PROFILES="${CLAUDE_USER_DATA:-${XDG_DATA_HOME:-$HOME/.local/share}/claude-plugins}/video-editing/render-profiles.json"
PROF=$(jq -r --arg n "$PROFILE_NAME" '.[$n] // empty' "$PROFILES")
[ -z "$PROF" ] && { echo "Profile not found: $PROFILE_NAME"; exit 1; }

VCODEC=$(jq -r '.vcodec' <<<"$PROF")
ACODEC=$(jq -r '.acodec // "aac"' <<<"$PROF")
WIDTH=$(jq -r '.width' <<<"$PROF")
HEIGHT=$(jq -r '.height' <<<"$PROF")
FPS=$(jq -r '.fps' <<<"$PROF")
QP=$(jq -r '.qp // empty' <<<"$PROF")
VB=$(jq -r '.vbitrate // empty' <<<"$PROF")
AB=$(jq -r '.abitrate // "192k"' <<<"$PROF")

Compose:

ARGS=( "$SRC" -consumer avformat:"$OUT" )
ARGS+=( vcodec="$VCODEC" acodec="$ACODEC" )
ARGS+=( width="$WIDTH" height="$HEIGHT" frame_rate_num="$FPS" frame_rate_den=1 )
[ -n "$QP" ] && ARGS+=( qp="$QP" )
[ -n "$VB" ] && ARGS+=( vb="$VB" )
ARGS+=( ab="$AB" )

3b. Inline params — prompt the user for the missing fields and build the same consumer chain.

Hardware encoders. melt uses libavformat under the hood, so VAAPI/NVENC encoder names match ffmpeg (h264_vaapi, hevc_nvenc, etc). However, melt does not set up the VAAPI hwupload chain automatically — for hardware-encoded renders the safer path is render to an intermediate (e.g. ProRes or h264 sw) via melt, then transcode to the GPU-encoded deliverable via render-with-profile. The skill should warn the user and offer this two-step path when a VAAPI/NVENC profile is selected.

4. Render

mkdir -p "$(dirname "$OUT")"
echo "Running: melt ${ARGS[*]}"
melt "${ARGS[@]}"

Show melt's progress output live.

5. Verify

ffprobe -v error -show_entries format=duration,size -of default=nw=1 "$OUT"

Print: output path, file size, duration, codec.

6. Confirm

Print the deliverable path. Offer to follow up with transcode (e.g. to make a YouTube-friendly version) or audio-analysis (to check loudness).

Notes

• For Kdenlive projects with proxy clips: melt resolves them via the project file's proxy paths. If the proxies have moved, the render will fail — fix the project paths in Kdenlive first.
• Render time is dominated by the most complex effect on the timeline; melt does not parallelize across CPU cores within a single track.
• Output container is inferred from the file extension (.mp4, .mkv, .mov).