sgl-project/sglang · error · Error

Previous frame size does not match current delta payload

Error message

Previous frame size does not match current delta payload

What it means

Raised when the stored previous frame's byte length differs from the size implied by the incoming delta payload, meaning the delta grid no longer aligns with the reference frame. Typically caused by a resolution change without a preceding keyframe or by corrupted stream data.

Solutions

1. Pad the tensor to a multiple of the pack width and slice afterwards
2. Round model dims (hidden size) to a multiple of 8
3. Use RCCL fallback for this tensor

Example fix

# before
det_ar(x)  # x.numel() % 4 != 0
# after
pad = (-x.numel()) % 4
det_ar(torch.nn.functional.pad(x.flatten(), (0, pad)))[:x.numel()]

d = 4  # fp32 pack width on ROCm
assert out.numel() % d == 0, f'size must be multiple of {d}'

When it happens

Trigger: Calling deterministic_all_reduce on a float32 tensor whose element count is not a multiple of the pack width.

Common situations: Non-multiple-of-pack hidden sizes or sliced tensors; fp32 master-weight reductions with odd lengths.

Related errors

• Error: --model-type requires a value.
• This browser does not support worker image decoding
• Unsupported content type
• Error: --model-type requires a non-empty value.
• Generate subcommand is not yet supported for model

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/48f1b7407d6a194e. Report an issue: GitHub.

Appendix: source

Thrown at python/sglang/multimodal_gen/apps/realtime_webui/decoder_worker.js:34

  }
  const stream = new Blob([payload]).stream().pipeThrough(new DecompressionStream("gzip"));
  return new Uint8Array(await new Response(stream).arrayBuffer());
}

async function restoreDeltaGzipFrames(header, payload) {
  const frameBytes = Number(header.bytes_per_frame);
  const count = Number(header.num_frames);
  const expectedSize = frameBytes * count;
  const restored = await gunzipBytes(payload);
  if (restored.length !== expectedSize) {
    throw new Error(`delta payload size mismatch: expected ${expectedSize}, got ${restored.length}`);
  }

  let previous = header.delta_reference === "previous-frame" ? lastFrame : null;
  if (header.delta_reference === "previous-frame") {
    if (!previous) throw new Error("Missing previous frame for delta payload");
    if (previous.byteLength !== frameBytes) {
      throw new Error("Previous frame size does not match current delta payload");
    }
  }

  for (let f = 0; f < count; f++) {
    const offset = f * frameBytes;
    if (previous) {
      for (let i = 0; i < frameBytes; i++) restored[offset + i] ^= previous[i];
    }
    previous = restored.slice(offset, offset + frameBytes);
  }
  lastFrame = previous;
  return restored;
}

function rawFramesToRgbaBuffers(header, payload) {
  const width = Number(header.width);
  const height = Number(header.height);
  const channels = Number(header.channels);

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