diff --git a/.github/workflows/regression.yml b/.github/workflows/regression.yml
index cffb29e8b..7e6f5b15f 100644
--- a/.github/workflows/regression.yml
+++ b/.github/workflows/regression.yml
@@ -75,9 +75,9 @@ jobs:
           - shard: shard-5
             args: "style-4-prod style-11-prod style-2-prod animejs-adapter typegpu-adapter parallel-capture-regression"
           - shard: shard-6
-            args: "overlay-montage-prod style-12-prod chat missing-host-comp-id png-sequence portrait-edge-bleed"
+            args: "overlay-montage-prod style-12-prod chat missing-host-comp-id png-sequence portrait-edge-bleed remote-media-localize"
           - shard: shard-7
-            args: "sub-composition-video style-18-prod raf-ball-render-compat font-variant-numeric sub-comp-t0 sub-comp-id-selector"
+            args: "sub-composition-video style-18-prod raf-ball-render-compat font-variant-numeric sub-comp-t0 sub-comp-id-selector audio-multi-track-mix"
           - shard: shard-8
             args: "style-13-prod style-6-prod vignelli-stacking gsap-letters-render-compat"
     steps:
diff --git a/packages/producer/tests/audio-multi-track-mix/meta.json b/packages/producer/tests/audio-multi-track-mix/meta.json
new file mode 100644
index 000000000..678a1656e
--- /dev/null
+++ b/packages/producer/tests/audio-multi-track-mix/meta.json
@@ -0,0 +1,15 @@
+{
+  "name": "Audio Multi-Track Mix",
+  "description": "Regression for PR #1140: amix normalize=0 crash on FFmpeg 4.x causing silent output. Three local audio tracks with staggered start times and distinct volumes; all three must be audible in the mix.",
+  "tags": ["audio", "regression", "amix"],
+
+  "minPsnr": 25,
+  "maxFrameFailures": 0,
+
+  "minAudioCorrelation": 0.85,
+  "maxAudioLagWindows": 60,
+
+  "renderConfig": {
+    "fps": 30
+  }
+}
diff --git a/packages/producer/tests/audio-multi-track-mix/output/.gitkeep b/packages/producer/tests/audio-multi-track-mix/output/.gitkeep
new file mode 100644
index 000000000..e69de29bb
diff --git a/packages/producer/tests/audio-multi-track-mix/output/compiled.html b/packages/producer/tests/audio-multi-track-mix/output/compiled.html
new file mode 100644
index 000000000..813cfde6a
--- /dev/null
+++ b/packages/producer/tests/audio-multi-track-mix/output/compiled.html
@@ -0,0 +1,54 @@
+<!DOCTYPE html>
+<html lang="en">
+<head><style data-hyperframes-text-rendering="true">html,body,*{text-rendering:geometricPrecision}</style>
+  <meta charset="UTF-8">
+  <title>Audio Multi-Track Mix</title>
+  <style>
+    html, body { margin: 0; padding: 0; background: #111; }
+    #root {
+      position: relative;
+      width: 1280px;
+      height: 720px;
+      background: #111;
+      display: flex;
+      align-items: center;
+      justify-content: center;
+      font-family: monospace;
+      color: #fff;
+    }
+    .label {
+      position: absolute;
+      font-size: 32px;
+      font-weight: bold;
+      letter-spacing: 0.05em;
+    }
+    #t1 { top: 180px; color: #4fc3f7; }
+    #t2 { top: 300px; color: #81c784; }
+    #t3 { top: 420px; color: #ffb74d; }
+  </style>
+</head>
+<body>
+  <!--
+    Regression fixture for PR #1140 (amix normalize=0 crash on FFmpeg 4.x).
+
+    Three audio tracks at different start times and volumes.
+    The mixer must produce a non-silent output with all tracks audible —
+    this catches any regression where amix options break the filter graph
+    and the output becomes silent.
+  -->
+  <div id="root" data-composition-id="main" data-width="1280" data-height="720" data-start="0" data-duration="4">
+    <!-- Track 1: 440 Hz tone, full duration, volume 0.6 -->
+    <audio id="track-1" src="assets/tone-440hz.wav" data-start="0" data-duration="4" data-volume="0.6" data-end="4"></audio>
+
+    <!-- Track 2: 660 Hz tone, starts at 0.5s, volume 0.8 -->
+    <audio id="track-2" src="assets/tone-660hz.wav" data-start="0.5" data-duration="3" data-volume="0.8" data-end="3.5"></audio>
+
+    <!-- Track 3: 880 Hz tone, starts at 1.5s, volume 1.0 -->
+    <audio id="track-3" src="assets/tone-880hz.wav" data-start="1.5" data-duration="2" data-volume="1.0" data-end="3.5"></audio>
+
+    <div class="label" id="t1">440 Hz — vol 0.6 (t=0s)</div>
+    <div class="label" id="t2">660 Hz — vol 0.8 (t=0.5s)</div>
+    <div class="label" id="t3">880 Hz — vol 1.0 (t=1.5s)</div>
+  </div>
+</body>
+</html>
diff --git a/packages/producer/tests/audio-multi-track-mix/output/output.mp4 b/packages/producer/tests/audio-multi-track-mix/output/output.mp4
new file mode 100644
index 000000000..b26e82fca
--- /dev/null
+++ b/packages/producer/tests/audio-multi-track-mix/output/output.mp4
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:10922c8ae4e60a5e2b649141cdf813a1ea87541c14551c7e23f3f8c166b687c9
+size 133299
diff --git a/packages/producer/tests/audio-multi-track-mix/src/assets/tone-440hz.wav b/packages/producer/tests/audio-multi-track-mix/src/assets/tone-440hz.wav
new file mode 100644
index 000000000..bde9cafed
Binary files /dev/null and b/packages/producer/tests/audio-multi-track-mix/src/assets/tone-440hz.wav differ
diff --git a/packages/producer/tests/audio-multi-track-mix/src/assets/tone-660hz.wav b/packages/producer/tests/audio-multi-track-mix/src/assets/tone-660hz.wav
new file mode 100644
index 000000000..64675f3c1
Binary files /dev/null and b/packages/producer/tests/audio-multi-track-mix/src/assets/tone-660hz.wav differ
diff --git a/packages/producer/tests/audio-multi-track-mix/src/assets/tone-880hz.wav b/packages/producer/tests/audio-multi-track-mix/src/assets/tone-880hz.wav
new file mode 100644
index 000000000..f67e266db
Binary files /dev/null and b/packages/producer/tests/audio-multi-track-mix/src/assets/tone-880hz.wav differ
diff --git a/packages/producer/tests/audio-multi-track-mix/src/index.html b/packages/producer/tests/audio-multi-track-mix/src/index.html
new file mode 100644
index 000000000..755e4c309
--- /dev/null
+++ b/packages/producer/tests/audio-multi-track-mix/src/index.html
@@ -0,0 +1,79 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <title>Audio Multi-Track Mix</title>
+  <style>
+    html, body { margin: 0; padding: 0; background: #111; }
+    #root {
+      position: relative;
+      width: 1280px;
+      height: 720px;
+      background: #111;
+      display: flex;
+      align-items: center;
+      justify-content: center;
+      font-family: monospace;
+      color: #fff;
+    }
+    .label {
+      position: absolute;
+      font-size: 32px;
+      font-weight: bold;
+      letter-spacing: 0.05em;
+    }
+    #t1 { top: 180px; color: #4fc3f7; }
+    #t2 { top: 300px; color: #81c784; }
+    #t3 { top: 420px; color: #ffb74d; }
+  </style>
+</head>
+<body>
+  <!--
+    Regression fixture for PR #1140 (amix normalize=0 crash on FFmpeg 4.x).
+
+    Three audio tracks at different start times and volumes.
+    The mixer must produce a non-silent output with all tracks audible —
+    this catches any regression where amix options break the filter graph
+    and the output becomes silent.
+  -->
+  <div
+    id="root"
+    data-composition-id="main"
+    data-width="1280"
+    data-height="720"
+    data-start="0"
+    data-duration="4"
+  >
+    <!-- Track 1: 440 Hz tone, full duration, volume 0.6 -->
+    <audio
+      id="track-1"
+      src="assets/tone-440hz.wav"
+      data-start="0"
+      data-duration="4"
+      data-volume="0.6"
+    ></audio>
+
+    <!-- Track 2: 660 Hz tone, starts at 0.5s, volume 0.8 -->
+    <audio
+      id="track-2"
+      src="assets/tone-660hz.wav"
+      data-start="0.5"
+      data-duration="3"
+      data-volume="0.8"
+    ></audio>
+
+    <!-- Track 3: 880 Hz tone, starts at 1.5s, volume 1.0 -->
+    <audio
+      id="track-3"
+      src="assets/tone-880hz.wav"
+      data-start="1.5"
+      data-duration="2"
+      data-volume="1.0"
+    ></audio>
+
+    <div class="label" id="t1">440 Hz — vol 0.6 (t=0s)</div>
+    <div class="label" id="t2">660 Hz — vol 0.8 (t=0.5s)</div>
+    <div class="label" id="t3">880 Hz — vol 1.0 (t=1.5s)</div>
+  </div>
+</body>
+</html>
diff --git a/packages/producer/tests/remote-media-localize/meta.json b/packages/producer/tests/remote-media-localize/meta.json
new file mode 100644
index 000000000..2e088ab50
--- /dev/null
+++ b/packages/producer/tests/remote-media-localize/meta.json
@@ -0,0 +1,15 @@
+{
+  "name": "Remote Media Localize",
+  "description": "Regression for PR #1146: remote S3 <video> and <audio> sources must be downloaded and rewritten to local paths before capture (skybound trailer: black frames + no audio). Also covers crossorigin strip on <audio> and <img> (PR #1140). The compiled.html snapshot verifies the src attributes are rewritten to _remote_media/.",
+  "tags": ["audio", "video", "regression", "remote-media", "crossorigin"],
+
+  "minPsnr": 25,
+  "maxFrameFailures": 3,
+
+  "minAudioCorrelation": 0.85,
+  "maxAudioLagWindows": 60,
+
+  "renderConfig": {
+    "fps": 30
+  }
+}
diff --git a/packages/producer/tests/remote-media-localize/output/.gitkeep b/packages/producer/tests/remote-media-localize/output/.gitkeep
new file mode 100644
index 000000000..e69de29bb
diff --git a/packages/producer/tests/remote-media-localize/output/compiled.html b/packages/producer/tests/remote-media-localize/output/compiled.html
new file mode 100644
index 000000000..463f37b8a
--- /dev/null
+++ b/packages/producer/tests/remote-media-localize/output/compiled.html
@@ -0,0 +1,56 @@
+<!DOCTYPE html>
+<html lang="en">
+<head><style data-hyperframes-text-rendering="true">html,body,*{text-rendering:geometricPrecision}</style>
+  <meta charset="UTF-8">
+  <title>Remote Media Localize</title>
+  <style>
+    html, body { margin: 0; padding: 0; background: #000; }
+    #root {
+      position: relative;
+      width: 1280px;
+      height: 720px;
+      background: #000;
+      overflow: hidden;
+    }
+    #bg-video {
+      position: absolute;
+      top: 0; left: 0;
+      width: 1280px;
+      height: 720px;
+      object-fit: cover;
+    }
+    .label {
+      position: absolute;
+      bottom: 40px;
+      left: 0; right: 0;
+      text-align: center;
+      font-family: monospace;
+      font-size: 28px;
+      color: #fff;
+      text-shadow: 0 2px 8px #000;
+    }
+  </style>
+</head>
+<body>
+  <!--
+    Regression fixture for PR #1146 (remote media localization) and
+    PR #1140 (crossorigin strip).
+
+    Before the fix: remote S3 src on video + audio elements caused black
+    frames (Chrome buffering timeout) and silent output (CORS rejection).
+
+    After the fix: localizeRemoteMediaSources() downloads the files and
+    rewrites src to _remote_media/ before render. crossorigin attrs stripped.
+    PSNR and audio correlation verify the fix actually works end-to-end.
+  -->
+  <div id="root" data-composition-id="main" data-width="1280" data-height="720" data-start="0" data-duration="4">
+    <!-- Remote video: must be localized to _remote_media/ and crossorigin stripped -->
+    <video id="bg-video" src="_remote_media/download_26528e90ebdf.mp4" data-start="0" data-duration="4" muted playsinline data-end="4" data-has-audio="false"></video>
+
+    <!-- Remote audio: src must be localized + crossorigin stripped -->
+    <audio id="bg-audio" src="_remote_media/download_1cb75829e1a1.wav" data-start="0" data-duration="4" data-volume="0.7" data-end="4"></audio>
+
+    <div class="label">remote-media-localize regression</div>
+  </div>
+</body>
+</html>
diff --git a/packages/producer/tests/remote-media-localize/output/output.mp4 b/packages/producer/tests/remote-media-localize/output/output.mp4
new file mode 100644
index 000000000..0b506f48f
--- /dev/null
+++ b/packages/producer/tests/remote-media-localize/output/output.mp4
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:e3fd2b16e66f5e93c4086af70058494785e0d4503b7eb4ef3439c8099b10426f
+size 1497430
diff --git a/packages/producer/tests/remote-media-localize/src/index.html b/packages/producer/tests/remote-media-localize/src/index.html
new file mode 100644
index 000000000..c66a4a6dd
--- /dev/null
+++ b/packages/producer/tests/remote-media-localize/src/index.html
@@ -0,0 +1,78 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <title>Remote Media Localize</title>
+  <style>
+    html, body { margin: 0; padding: 0; background: #000; }
+    #root {
+      position: relative;
+      width: 1280px;
+      height: 720px;
+      background: #000;
+      overflow: hidden;
+    }
+    #bg-video {
+      position: absolute;
+      top: 0; left: 0;
+      width: 1280px;
+      height: 720px;
+      object-fit: cover;
+    }
+    .label {
+      position: absolute;
+      bottom: 40px;
+      left: 0; right: 0;
+      text-align: center;
+      font-family: monospace;
+      font-size: 28px;
+      color: #fff;
+      text-shadow: 0 2px 8px #000;
+    }
+  </style>
+</head>
+<body>
+  <!--
+    Regression fixture for PR #1146 (remote media localization) and
+    PR #1140 (crossorigin strip).
+
+    Before the fix: remote S3 src on video + audio elements caused black
+    frames (Chrome buffering timeout) and silent output (CORS rejection).
+
+    After the fix: localizeRemoteMediaSources() downloads the files and
+    rewrites src to _remote_media/ before render. crossorigin attrs stripped.
+    PSNR and audio correlation verify the fix actually works end-to-end.
+  -->
+  <div
+    id="root"
+    data-composition-id="main"
+    data-width="1280"
+    data-height="720"
+    data-start="0"
+    data-duration="4"
+  >
+    <!-- Remote video: must be localized to _remote_media/ and crossorigin stripped -->
+    <video
+      id="bg-video"
+      src="https://gen-os-static.s3.us-east-2.amazonaws.com/astral_assets/uploaded_assets/12ca139c_8bf35a3b61b84ab69251ad5091e4c69b.mp4"
+      crossorigin="anonymous"
+      data-start="0"
+      data-duration="4"
+      muted
+      playsinline
+    ></video>
+
+    <!-- Remote audio: src must be localized + crossorigin stripped -->
+    <audio
+      id="bg-audio"
+      src="https://gen-os-static.s3.us-east-2.amazonaws.com/astral_assets/generated_assets/f87f97d4_0c49f6fa95224cc3bd4f5ea3a0d937c5.wav"
+      crossorigin="anonymous"
+      data-start="0"
+      data-duration="4"
+      data-volume="0.7"
+    ></audio>
+
+    <div class="label">remote-media-localize regression</div>
+  </div>
+</body>
+</html>
