🎈LG_ConcatVideoFiles

If your video workflow produces segments - separate clips for shots, or per-scene generations - LG_ConcatVideoFiles is the glue. It takes a list of video file paths, joins them with FFmpeg's concat demuxer, and optionally replaces or mixes in an audio track, then returns the merged file's path. The output is a STRING, so you can chain it straight after LG_CreateAndSaveVideo and keep everything in the graph instead of stitching clips by hand afterward.

It's a video helper in Comfyui-LG_GroupExecutor, LAOGOU-666's small pack. It's one of the few nodes here with a real external dependency: it shells out to ffmpeg, so that binary needs to be findable on your PATH.

How it works

The video_paths input accepts a list of paths, a single path, or even multiline text (it splits on newlines). Each path is validated to exist, then written into an FFmpeg concat list and joined. The key toggle is reencode:

• False (default) - direct concat. -c copy copies streams without re-encoding: fast, lossless, but demands the segments share codec, resolution, and fps. If the clips are uniform (say, all H.264 mp4s from the same generator), this is instant.
• True - re-encode. libx264 -preset medium -crf 23 (with AAC audio). Slower, but it normalizes mismatched segments so nearly anything joins.

The audio handling runs as a second FFmpeg pass: replace swaps in your audio_path as the new soundtrack, mix uses an amix filter to blend original and new audio, and audio_volume (0–2) scales the result. A missing audio file is skipped with a warning rather than aborting the whole merge.

Inputs & outputs

• video_paths (STRING, list-capable) - the segments.
• filename_prefix (STRING, default video/merged) - output location.
• reencode (BOOLEAN) - fast-copy vs compatible re-encode.
• audio_path (STRING) - optional audio file.
• audio_mode - replace (default) or mix.
• audio_volume (FLOAT, 0–2, default 1.0).

Output: output_path (STRING) - the merged mp4.

Install

cd ComfyUI/custom_nodes
git clone https://github.com/LAOGOU-666/Comfyui-LG_GroupExecutor

or via ComfyUI Manager → "Comfyui-LG_GroupExecutor", then restart. And make sure ffmpeg is on your PATH - ffmpeg -version in a terminal is the check. ComfyUI's bundled Python env usually carries it, but if the node errors with an FFmpeg subprocess failure, that's where to look.

Where people get burned

• -c copy fails on mismatched segments (different resolutions/fps). The error message is FFmpeg's, and it's usually cryptic - just flip reencode on.
• Fast concat + audio is still two passes, so even in fast mode an audio swap isn't instant.
• Paths are used as-is, so relative vs absolute matters - feed it the absolute paths that LG_CreateAndSaveVideo returns.