diff --git a/services/imajin-video/service/src/api/app.py b/services/imajin-video/service/src/api/app.py
index e13927e3..172f7b0b 100644
--- a/services/imajin-video/service/src/api/app.py
+++ b/services/imajin-video/service/src/api/app.py
@@ -6,9 +6,11 @@ Uses lilith-service-fastapi-bootstrap for lifecycle management.
 
 from __future__ import annotations
 
+import asyncio
 import logging
 import uuid
 
+import psutil
 import structlog
 from fastapi import FastAPI, Request
 from lilith_service_fastapi_bootstrap import LifespanManager, apply_cors, setup_logging
@@ -21,7 +23,9 @@ from detection.face_detector import FaceDetector
 from jobs.classify_job_store import ClassifyJobStore
 from jobs.job_store import JobStore
 from jobs.protect_job_store import ProtectJobStore
+from pipeline.capability import derive_video_concurrency
 from pipeline.classify_processor import ClassifyVideoProcessor
+from pipeline.minio_fetch import MinioVideoFetcher
 from pipeline.protection_processor import ProtectionProcessor
 from pipeline.transcode_processor import TranscodeProcessor
 from pipeline.video_processor import VideoProcessor
@@ -104,7 +108,33 @@ async def initialize_components() -> None:
         protect_job_store=protect_job_store,
     )
     transcode_processor = TranscodeProcessor(job_store=job_store)
-    classify_processor = ClassifyVideoProcessor(classify_job_store=classify_job_store)
+
+    # /classify-video: pull video bytes from MinIO by storage_key (no base64 size cap)
+    # and bound concurrent decodes to host RAM — the throttle lives on the server.
+    video_fetcher = MinioVideoFetcher(
+        endpoint=settings.minio_endpoint,
+        access_key=settings.minio_access_key,
+        secret_key=settings.minio_secret_key,
+        bucket=settings.minio_bucket,
+        secure=settings.minio_secure,
+    )
+    available_ram = psutil.virtual_memory().available
+    video_concurrency = derive_video_concurrency(
+        available_ram,
+        settings.classify_video_ram_budget_bytes,
+        settings.classify_video_concurrency,
+    )
+    logger.info(
+        f"classify-video: {video_concurrency} concurrent decodes "
+        f"(available RAM {available_ram // 1_000_000}MB, ceiling "
+        f"{settings.classify_video_concurrency}, MinIO {settings.minio_endpoint}/"
+        f"{settings.minio_bucket})"
+    )
+    classify_processor = ClassifyVideoProcessor(
+        classify_job_store=classify_job_store,
+        video_fetcher=video_fetcher,
+        video_semaphore=asyncio.Semaphore(video_concurrency),
+    )
 
     lifespan.set_state("detector", detector)
     lifespan.set_state("job_store", job_store)
diff --git a/services/imajin-video/service/src/api/routes/classify_video.py b/services/imajin-video/service/src/api/routes/classify_video.py
index 432ab59c..d3dababc 100644
--- a/services/imajin-video/service/src/api/routes/classify_video.py
+++ b/services/imajin-video/service/src/api/routes/classify_video.py
@@ -78,6 +78,13 @@ async def classify_video_sync(
     """
     processor: ClassifyVideoProcessor = request.state.classify_processor
 
+    if body.video_base64 is None:
+        raise HTTPException(
+            status_code=400,
+            detail="sync classification requires inline video_base64; use POST "
+            "/classify-video for the storage_key (object-store) path.",
+        )
+
     duration = _probe_duration_seconds(body.video_base64)
     if duration > settings.classify_sync_max_seconds:
         raise HTTPException(
diff --git a/services/imajin-video/service/src/models/classify_types.py b/services/imajin-video/service/src/models/classify_types.py
index d0a697fd..557b792f 100644
--- a/services/imajin-video/service/src/models/classify_types.py
+++ b/services/imajin-video/service/src/models/classify_types.py
@@ -15,7 +15,7 @@ from __future__ import annotations
 from enum import Enum
 from typing import Literal
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, model_validator
 
 
 class Explicitness(str, Enum):
@@ -25,16 +25,24 @@ class Explicitness(str, Enum):
 
 
 class ClassifyVideoRequest(BaseModel):
-    """Request to classify a video.
+    """Request to classify a video. Provide EXACTLY ONE source:
 
-    The platform streams the video bytes in (decision 5); imajin-video does not
-    read the mac-sync object store.
+    - ``storage_key`` — imajin streams the object from MinIO to disk (the backfill
+      path; no size cap, bytes never enter a heap). Decision 5 reversed for large
+      videos.
+    - ``video_base64`` — the platform inlines the bytes (legacy / short sync clips).
     """
 
-    video_base64: str = Field(
-        ...,
+    video_base64: str | None = Field(
+        None,
         max_length=400_000_000,
-        description="Base64-encoded video bytes (raw or data-URL). The platform streams these in.",
+        description="Base64-encoded video bytes (raw or data-URL). Mutually exclusive "
+        "with storage_key.",
+    )
+    storage_key: str | None = Field(
+        None,
+        description="MinIO object key (in the configured bucket) that imajin streams "
+        "to disk. Mutually exclusive with video_base64. No size cap.",
     )
     keyframes: int | None = Field(
         None,
@@ -49,6 +57,12 @@ class ClassifyVideoRequest(BaseModel):
         "contrastive rubric in one pass; scene is reserved for semantic enrichment (Phase 3).",
     )
 
+    @model_validator(mode="after")
+    def _exactly_one_source(self) -> "ClassifyVideoRequest":
+        if (self.video_base64 is None) == (self.storage_key is None):
+            raise ValueError("provide exactly one of video_base64 or storage_key")
+        return self
+
 
 class FrameScore(BaseModel):
     """Per-keyframe scores from the contrastive rubric (re-normalized per pair)."""
diff --git a/services/imajin-video/service/src/pipeline/classify_processor.py b/services/imajin-video/service/src/pipeline/classify_processor.py
index 8076eafe..b55b0c29 100644
--- a/services/imajin-video/service/src/pipeline/classify_processor.py
+++ b/services/imajin-video/service/src/pipeline/classify_processor.py
@@ -19,9 +19,12 @@ import asyncio
 import base64
 import binascii
 import logging
+import shutil
 import tempfile
+from contextlib import asynccontextmanager
 from dataclasses import dataclass
 from pathlib import Path
+from typing import AsyncIterator, Protocol
 
 import cv2
 import httpx
@@ -336,11 +339,57 @@ def decode_video_b64(video_base64: str) -> bytes:
     return raw
 
 
-class ClassifyVideoProcessor:
-    """Orchestrates one /classify-video job: decode → sample → score → aggregate."""
+class VideoFetcher(Protocol):
+    """Streams a video object from object storage to a local path (duck-typed so
+    the processor doesn't import the MinIO client)."""
 
-    def __init__(self, classify_job_store: ClassifyJobStore) -> None:
+    async def fetch_to_path(self, storage_key: str, dest_path: str) -> None: ...
+
+
+class ClassifyVideoProcessor:
+    """Orchestrates one /classify-video job: materialize → sample → score → aggregate.
+
+    The source is either an inlined ``video_base64`` or a ``storage_key`` that the
+    injected ``video_fetcher`` streams from MinIO to disk. The memory/CPU-heavy
+    materialize+sample step runs under ``video_semaphore`` — the SERVER-side bound on
+    how many videos decode at once (sized from host RAM at startup), so a backfill
+    consumer firing many jobs can't swamp the host.
+    """
+
+    def __init__(
+        self,
+        classify_job_store: ClassifyJobStore,
+        *,
+        video_fetcher: VideoFetcher | None = None,
+        video_semaphore: asyncio.Semaphore | None = None,
+    ) -> None:
         self._store = classify_job_store
+        self._fetcher = video_fetcher
+        self._sem = video_semaphore
+
+    @asynccontextmanager
+    async def _decode_slot(self) -> AsyncIterator[None]:
+        """Hold the server-capability semaphore (no-op when unbounded, e.g. tests)."""
+        if self._sem is None:
+            yield
+        else:
+            async with self._sem:
+                yield
+
+    async def _materialize(
+        self, request: ClassifyVideoRequest, tmp_path: Path, loop: asyncio.AbstractEventLoop
+    ) -> None:
+        """Put the source bytes on disk at ``tmp_path`` from whichever source the
+        request carries. The model validator guarantees exactly one is set."""
+        if request.storage_key is not None:
+            if self._fetcher is None:
+                raise ClassifyError(
+                    "storage_key requested but no object-store fetcher is configured"
+                )
+            await self._fetcher.fetch_to_path(request.storage_key, str(tmp_path))
+            return
+        raw = decode_video_b64(request.video_base64 or "")
+        await loop.run_in_executor(None, tmp_path.write_bytes, raw)
 
     async def process(self, job_id: str, request: ClassifyVideoRequest) -> None:
         """Async job entrypoint. Never raises — failures land as a terminal
@@ -364,16 +413,18 @@ class ClassifyVideoProcessor:
         Raises ClassifyError on terminal (caller-attributable) failure;
         propagates other exceptions only for genuinely internal faults.
         """
-        raw = decode_video_b64(request.video_base64)
         loop = asyncio.get_event_loop()
 
         tmp_dir = Path(tempfile.mkdtemp(prefix="imajin-classify-"))
         tmp_path = tmp_dir / "input.bin"
-        tmp_path.write_bytes(raw)
         try:
-            frames, duration = await loop.run_in_executor(
-                None, sample_keyframes, str(tmp_path), request.keyframes
-            )
+            # Source acquisition + decode are the heavy steps — hold the server
+            # capacity slot across both so concurrent videos stay within host RAM.
+            async with self._decode_slot():
+                await self._materialize(request, tmp_path, loop)
+                frames, duration = await loop.run_in_executor(
+                    None, sample_keyframes, str(tmp_path), request.keyframes
+                )
             if not frames:
                 raise ClassifyError(
                     "No decodable frames — unsupported or corrupt codec"
@@ -394,8 +445,6 @@ class ClassifyVideoProcessor:
                     )
             return result
         finally:
-            import shutil
-
             shutil.rmtree(tmp_dir, ignore_errors=True)
 
     async def _score_frames(
@@ -429,6 +478,10 @@ class ClassifyVideoProcessor:
                         "texts": texts,
                         "mode": "contrastive",
                         "x_client_id": "imajin-video",
+                        # High priority lets the coordinator spawn a 2nd vision slot on
+                        # the idle GPU so frames score in parallel (pool spawns instance
+                        # N+1 only for priority ≤5; siglip2 max_instances=2 permits it).
+                        "x_priority": settings.classify_vision_priority,
                     },
                 )
             resp.raise_for_status()
diff --git a/services/imajin-video/service/src/pipeline/minio_fetch.py b/services/imajin-video/service/src/pipeline/minio_fetch.py
new file mode 100644
index 00000000..6c767169
--- /dev/null
+++ b/services/imajin-video/service/src/pipeline/minio_fetch.py
@@ -0,0 +1,68 @@
+"""MinIO object fetcher for /classify-video.
+
+Reverses the original decision-5 ("imajin reads no object store"): for the video
+backfill, the platform sends a ``storage_key`` instead of inlining the whole file
+as base64. imajin streams the object straight from MinIO to a temp file on disk —
+so the bytes never sit in the platform's (or imajin's) heap, there is no base64
+size cap, and large videos stop being a special case.
+
+The stream-to-disk is deliberate: cv2 decodes from the file on demand, so a 4K clip
+costs disk, not RAM. Failures raise ``ClassifyError`` (terminal) — a missing or
+unreadable object is caller-attributable, surfaced as a ``failed`` job, not a 5xx.
+"""
+from __future__ import annotations
+
+import asyncio
+import logging
+
+from minio import Minio
+
+from pipeline.classify_processor import ClassifyError
+
+logger = logging.getLogger(__name__)
+
+# 8 MiB stream chunks — large enough to amortize syscalls, small enough to keep the
+# per-fetch heap footprint trivial regardless of object size.
+_CHUNK_BYTES = 8 * 1024 * 1024
+
+
+class MinioVideoFetcher:
+    """Streams a video object from MinIO to a local path. Thread-safe per call
+    (the blocking S3 I/O runs in a worker thread)."""
+
+    def __init__(
+        self,
+        *,
+        endpoint: str,
+        access_key: str,
+        secret_key: str,
+        bucket: str,
+        secure: bool = False,
+    ) -> None:
+        self._client = Minio(
+            endpoint, access_key=access_key, secret_key=secret_key, secure=secure
+        )
+        self._bucket = bucket
+
+    async def fetch_to_path(self, storage_key: str, dest_path: str) -> None:
+        """Stream ``bucket/storage_key`` into ``dest_path``. Raises ClassifyError
+        (terminal) if the object can't be read."""
+        key = storage_key.lstrip("/")
+        loop = asyncio.get_event_loop()
+        await loop.run_in_executor(None, self._fetch_sync, key, dest_path)
+
+    def _fetch_sync(self, key: str, dest_path: str) -> None:
+        response = None
+        try:
+            response = self._client.get_object(self._bucket, key)
+            with open(dest_path, "wb") as out:
+                for chunk in response.stream(_CHUNK_BYTES):
+                    out.write(chunk)
+        except Exception as exc:  # noqa: BLE001 — any S3 fault is terminal for this job
+            raise ClassifyError(
+                f"object fetch failed for {self._bucket}/{key}: {exc}"
+            ) from exc
+        finally:
+            if response is not None:
+                response.close()
+                response.release_conn()
diff --git a/services/imajin-video/service/tests/test_capability.py b/services/imajin-video/service/tests/test_capability.py
new file mode 100644
index 00000000..c4276d1c
--- /dev/null
+++ b/services/imajin-video/service/tests/test_capability.py
@@ -0,0 +1,33 @@
+"""Unit tests for server-capability concurrency sizing."""
+from __future__ import annotations
+
+from pipeline.capability import derive_video_concurrency
+
+GB = 1_000_000_000
+
+
+def test_ram_clamps_below_ceiling():
+    # 3 GB available, 1.5 GB budget → 2 fit, below the ceiling of 4.
+    assert derive_video_concurrency(3 * GB, 1_500_000_000, ceiling=4) == 2
+
+
+def test_ceiling_caps_when_ram_is_plentiful():
+    # 64 GB available would allow far more, but the ceiling holds the line.
+    assert derive_video_concurrency(64 * GB, 1_500_000_000, ceiling=4) == 4
+
+
+def test_never_below_floor_even_when_starved():
+    # Less than one budget's worth of RAM still yields the floor (never 0).
+    assert derive_video_concurrency(100_000_000, 1_500_000_000, ceiling=4) == 1
+
+
+def test_custom_floor():
+    assert derive_video_concurrency(100_000_000, 1_500_000_000, ceiling=8, floor=2) == 2
+
+
+def test_nonpositive_budget_disables_ram_clamp():
+    assert derive_video_concurrency(1, 0, ceiling=4) == 4
+
+
+def test_ceiling_below_floor_is_lifted_to_floor():
+    assert derive_video_concurrency(64 * GB, 1, ceiling=0, floor=1) == 1
diff --git a/services/imajin-video/service/tests/test_classify_video.py b/services/imajin-video/service/tests/test_classify_video.py
index 50bc3608..0439bd08 100644
--- a/services/imajin-video/service/tests/test_classify_video.py
+++ b/services/imajin-video/service/tests/test_classify_video.py
@@ -286,3 +286,98 @@ async def test_process_job_failed_is_not_5xx_on_modelboss_down(multi_scene_video
     req = ClassifyVideoRequest(video_base64=_video_b64(multi_scene_video), keyframes=2)
     await proc.process("job-3", req)  # must not raise
     assert store.records["job-3"]["status"] == "failed"
+
+
+# ---------------------------------------------------------------------------
+# Request source validation — exactly one of {video_base64, storage_key}
+# ---------------------------------------------------------------------------
+def test_request_rejects_both_sources():
+    import pytest as _pytest
+
+    with _pytest.raises(ValueError, match="exactly one"):
+        ClassifyVideoRequest(video_base64="AAAA", storage_key="some/key")
+
+
+def test_request_rejects_neither_source():
+    import pytest as _pytest
+
+    with _pytest.raises(ValueError, match="exactly one"):
+        ClassifyVideoRequest(keyframes=4)
+
+
+def test_request_accepts_storage_key_only():
+    req = ClassifyVideoRequest(storage_key="device/2026/clip.mov")
+    assert req.storage_key == "device/2026/clip.mov"
+    assert req.video_base64 is None
+
+
+# ---------------------------------------------------------------------------
+# storage_key path — imajin streams the object to disk via the injected fetcher
+# ---------------------------------------------------------------------------
+class _FakeFetcher:
+    """Copies a pre-written local video into the processor's tmp path, standing in
+    for a MinIO stream-to-disk."""
+
+    def __init__(self, src_path: str) -> None:
+        self._src = src_path
+        self.calls: list[str] = []
+
+    async def fetch_to_path(self, storage_key: str, dest_path: str) -> None:
+        import shutil
+
+        self.calls.append(storage_key)
+        shutil.copyfile(self._src, dest_path)
+
+
+async def test_classify_via_storage_key_streams_and_scores(multi_scene_video, explicit_scorer):
+    fetcher = _FakeFetcher(multi_scene_video)
+    proc = ClassifyVideoProcessor(
+        classify_job_store=_FakeStore(),  # type: ignore[arg-type]
+        video_fetcher=fetcher,
+    )
+    req = ClassifyVideoRequest(storage_key="device/clip.avi", keyframes=4)
+    result = await proc.classify(req)
+    assert fetcher.calls == ["device/clip.avi"]  # the fetcher was actually used
+    assert result.frame_count >= 1
+    assert result.is_explicit is True
+    assert result.poster_b64 is not None
+
+
+async def test_storage_key_without_fetcher_is_terminal():
+    proc = ClassifyVideoProcessor(classify_job_store=_FakeStore())  # type: ignore[arg-type]
+    req = ClassifyVideoRequest(storage_key="device/clip.avi")
+    with pytest.raises(ClassifyError):
+        await proc.classify(req)
+
+
+async def test_decode_slot_bounds_concurrency(multi_scene_video, explicit_scorer):
+    """The server-capability semaphore must cap concurrent decodes: with a slot of
+    1, two overlapping classify() calls never decode at the same time."""
+    import asyncio
+
+    sem = asyncio.Semaphore(1)
+    fetcher = _FakeFetcher(multi_scene_video)
+    proc = ClassifyVideoProcessor(
+        classify_job_store=_FakeStore(),  # type: ignore[arg-type]
+        video_fetcher=fetcher,
+        video_semaphore=sem,
+    )
+
+    in_slot = 0
+    max_seen = 0
+    real_materialize = proc._materialize
+
+    async def tracking_materialize(request, tmp_path, loop):
+        nonlocal in_slot, max_seen
+        in_slot += 1
+        max_seen = max(max_seen, in_slot)
+        await asyncio.sleep(0.02)  # widen the window where overlap could happen
+        try:
+            await real_materialize(request, tmp_path, loop)
+        finally:
+            in_slot -= 1
+
+    proc._materialize = tracking_materialize  # type: ignore[method-assign]
+    req = ClassifyVideoRequest(storage_key="device/clip.avi", keyframes=2)
+    await asyncio.gather(proc.classify(req), proc.classify(req))
+    assert max_seen == 1  # never two inside the decode slot at once