About

Combining multiple animated GIFs into a single composite file requires frame-level synchronization. Each source GIF may have a different frame count (n), frame delay (d), and canvas size. This tool decodes every source GIF to its raw frames, computes a synchronized timeline using the least common multiple of frame counts, composites each frame onto a grid layout at the target resolution, then re-encodes the result as a valid GIF89a file with LZW compression. Getting the timing wrong produces jarring stutters. Getting the palette wrong produces color banding. A naive approach of screen-recording a browser window yields lossy artifacts and uncontrolled file sizes. This tool operates at the binary level: it reads and writes the GIF specification directly. Note: output is limited to 256 colors per the GIF specification. Source GIFs with vastly different palettes will undergo median-cut quantization, which may shift subtle gradients.

Formulas

The total number of output frames is determined by synchronizing all source GIFs so each completes full cycles:

F_out = lcm(n₁, n₂, …, n_k)

where n_i is the frame count of the i-th source GIF and k is the total number of source GIFs. The output frame delay is the minimum delay across sources, clamped to the browser floor:

d_out = max(min(d₁, d₂, …, d_k), 20ms)

The output canvas dimensions for a grid of c columns and r rows with padding p and cell size s:

W = c × s + (c + 1) × p

H = r × s + (r + 1) × p

where s is computed from the user-specified cell pixel size. LZW compression operates on a dictionary of pixel index sequences, starting from initial code size m = max(2, ceil(log₂(colors))). The clear code is 2^m and EOI code is 2^m + 1.

Reference Data

Parameter	GIF87a	GIF89a	Notes
Max Colors	256	256	Per frame (local color table)
Transparency	No	Yes	Via Graphic Control Extension
Animation	No	Yes	Multiple image blocks + GCE
Loop Control	N/A	Netscape Extension	0 = infinite loop
Min Frame Delay	N/A	10ms	Browsers clamp to ~20ms
LZW Min Code Size	2 - 8	2 - 8	Matches color table bit depth
Max Image Dimension	65535px	65535px	Spec limit; practical ~4000px
Disposal Method 0	N/A	Unspecified	No action required
Disposal Method 1	N/A	Do Not Dispose	Frame persists
Disposal Method 2	N/A	Restore to BG	Clear to background color
Disposal Method 3	N/A	Restore to Previous	Restore canvas state
Interlacing	Yes	Yes	4-pass Adam7-like scheme
Typical Web Delay	N/A	100ms	10 FPS common default
Header Bytes	6	6	`GIF87a` / `GIF89a`
Logical Screen Desc.	7 bytes	7 bytes	Width, Height, flags, BG, aspect
Trailer Byte	0x3B	0x3B	Marks end of data stream

Frequently Asked Questions

The GIF format permits a maximum of 256 colors per frame. When combining multiple GIFs, each with its own palette, the tool must quantize all colors into a single global palette using median-cut. Source GIFs with smooth gradients or vastly different color profiles will show quantization artifacts. Reducing the number of source GIFs or using sources with similar palettes minimizes this effect.

The tool computes the least common multiple (LCM) of all source frame counts. For example, if GIF A has 10 frames and GIF B has 15 frames, the output will have lcm(10, 15) = 30 frames. Each source loops until all sources complete a full cycle. The LCM is capped at 120 frames to prevent excessive file sizes.

The tool supports up to 9 source GIFs in a 3×3 grid. Each source file should be under 5MB. Larger files or more sources exponentially increase encoding time and output file size. A 4-GIF grid at 150px cell size with 30 frames typically produces a 1 - 3MB output.

GIF encoding involves LZW compression of every pixel in every frame. A 300×300px output with 60 frames processes 5.4 million pixels. The tool offloads encoding to a Web Worker so your browser remains responsive. Progress is reported in real-time. Reducing cell size or frame count significantly speeds up encoding.

Transparent pixels in source GIFs are rendered against the configured background color during compositing. The output GIF does not preserve per-source transparency. If you need transparency in the output, set the background color to a unique value and note that GIF transparency is binary (no alpha blending). Partially transparent pixels will be fully opaque in the output.

Currently all sources begin at frame 0 and loop forward. To offset a source, you would need to pre-edit it externally so frame 0 is your desired start point. The tool synchronizes all sources from their first frame simultaneously.