diff --git a/src/prebid.js b/src/prebid.js
index 94ade8e5f83..5c5f66d6028 100644
--- a/src/prebid.js
+++ b/src/prebid.js
@@ -52,6 +52,7 @@ import {newMetrics, useMetrics} from './utils/perfMetrics.js';
 import {defer, GreedyPromise} from './utils/promise.js';
 import {enrichFPD} from './fpd/enrichment.js';
 import {allConsent} from './consentHandler.js';
+import {fillVideoDefaults} from './video.js';
 
 const pbjsInstance = getGlobal();
 const { triggerUserSyncs } = userSync;
@@ -269,6 +270,12 @@ export const checkAdUnitSetup = hook('sync', function (adUnits) {
   return validatedAdUnits;
 }, 'checkAdUnitSetup');
 
+function fillAdUnitDefaults(adUnits) {
+  if (FEATURES.VIDEO) {
+    adUnits.forEach(au => fillVideoDefaults(au))
+  }
+}
+
 /// ///////////////////////////////
 //                              //
 //    Start Public APIs         //
@@ -658,6 +665,7 @@ pbjsInstance.requestBids = (function() {
 
 export const startAuction = hook('async', function ({ bidsBackHandler, timeout: cbTimeout, adUnits, ttlBuffer, adUnitCodes, labels, auctionId, ortb2Fragments, metrics, defer } = {}) {
   const s2sBidders = getS2SBidderSet(config.getConfig('s2sConfig') || []);
+  fillAdUnitDefaults(adUnits);
   adUnits = useMetrics(metrics).measureTime('requestBids.validate', () => checkAdUnitSetup(adUnits));
 
   function auctionDone(bids, timedOut, auctionId) {
diff --git a/src/video.js b/src/video.js
index 7930e318874..90539306011 100644
--- a/src/video.js
+++ b/src/video.js
@@ -1,25 +1,21 @@
-import adapterManager from './adapterManager.js';
-import { deepAccess, logError } from './utils.js';
-import { config } from '../src/config.js';
-import {includes} from './polyfill.js';
-import { hook } from './hook.js';
+import {deepAccess, logError} from './utils.js';
+import {config} from '../src/config.js';
+import {hook} from './hook.js';
 import {auctionManager} from './auctionManager.js';
 
-const VIDEO_MEDIA_TYPE = 'video';
 export const OUTSTREAM = 'outstream';
 export const INSTREAM = 'instream';
 
-/**
- * Helper functions for working with video-enabled adUnits
- */
-export const videoAdUnit = adUnit => {
-  const mediaType = adUnit.mediaType === VIDEO_MEDIA_TYPE;
-  const mediaTypes = deepAccess(adUnit, 'mediaTypes.video');
-  return mediaType || mediaTypes;
-};
-export const videoBidder = bid => includes(adapterManager.videoAdapters, bid.bidder);
-export const hasNonVideoBidder = adUnit =>
-  adUnit.bids.filter(bid => !videoBidder(bid)).length;
+export function fillVideoDefaults(adUnit) {
+  const video = adUnit?.mediaTypes?.video;
+  if (video != null && video.plcmt == null) {
+    if (video.context === OUTSTREAM || [2, 3, 4].includes(video.placement)) {
+      video.plcmt = 4;
+    } else if (video.context !== OUTSTREAM && [2, 6].includes(video.playmethod)) {
+      video.plcmt = 2;
+    }
+  }
+}
 
 /**
  * @typedef {object} VideoBid
diff --git a/test/spec/video_spec.js b/test/spec/video_spec.js
index 61621c7ec42..0911f087587 100644
--- a/test/spec/video_spec.js
+++ b/test/spec/video_spec.js
@@ -1,4 +1,4 @@
-import { isValidVideoBid } from 'src/video.js';
+import {fillVideoDefaults, isValidVideoBid} from 'src/video.js';
 import {hook} from '../../src/hook.js';
 import {stubAuctionIndex} from '../helpers/indexStub.js';
 
@@ -7,97 +7,169 @@ describe('video.js', function () {
     hook.ready();
   });
 
-  it('validates valid instream bids', function () {
-    const bid = {
-      adId: '456xyz',
-      vastUrl: 'http://www.example.com/vastUrl',
-      transactionId: 'au'
-    };
-    const adUnits = [{
-      transactionId: 'au',
-      mediaTypes: {
-        video: {context: 'instream'}
-      }
-    }];
-    const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
-    expect(valid).to.equal(true);
-  });
+  describe('fillVideoDefaults', () => {
+    function fillDefaults(videoMediaType = {}) {
+      const adUnit = {mediaTypes: {video: videoMediaType}};
+      fillVideoDefaults(adUnit);
+      return adUnit.mediaTypes.video;
+    }
 
-  it('catches invalid instream bids', function () {
-    const bid = {
-      transactionId: 'au'
-    };
-    const adUnits = [{
-      transactionId: 'au',
-      mediaTypes: {
-        video: {context: 'instream'}
-      }
-    }];
-    const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
-    expect(valid).to.equal(false);
-  });
+    describe('should set plcmt = 4 when', () => {
+      it('context is "outstream"', () => {
+        expect(fillDefaults({context: 'outstream'})).to.eql({
+          context: 'outstream',
+          plcmt: 4
+        })
+      });
+      [2, 3, 4].forEach(placement => {
+        it(`placemement is "${placement}"`, () => {
+          expect(fillDefaults({placement})).to.eql({
+            placement,
+            plcmt: 4
+          });
+        })
+      });
+    });
+    describe('should set plcmt = 2 when', () => {
+      [2, 6].forEach(playmethod => {
+        it(`playmethod is "${playmethod}"`, () => {
+          expect(fillDefaults({playmethod})).to.eql({
+            playmethod,
+            plcmt: 2,
+          });
+        });
+      });
+    });
+    describe('should not set plcmt when', () => {
+      Object.entries({
+        'it was set by pub (context=outstream)': {
+          expected: 1,
+          video: {
+            context: 'outstream',
+            plcmt: 1
+          }
+        },
+        'it was set by pub (placement=2)': {
+          expected: 1,
+          video: {
+            placement: 2,
+            plcmt: 1
+          }
+        },
+        'placement not in 2, 3, 4': {
+          expected: undefined,
+          video: {
+            placement: 1
+          }
+        },
+        'it was set by pub (playmethod=2)': {
+          expected: 1,
+          video: {
+            plcmt: 1,
+            playmethod: 2
+          }
+        }
+      }).forEach(([t, {expected, video}]) => {
+        it(t, () => {
+          expect(fillDefaults(video).plcmt).to.eql(expected);
+        })
+      })
+    })
+  })
 
-  it('catches invalid bids when prebid-cache is disabled', function () {
-    const adUnits = [{
-      transactionId: 'au',
-      bidder: 'vastOnlyVideoBidder',
-      mediaTypes: {video: {}},
-    }];
+  describe('isValidVideoBid', () => {
+    it('validates valid instream bids', function () {
+      const bid = {
+        adId: '456xyz',
+        vastUrl: 'http://www.example.com/vastUrl',
+        transactionId: 'au'
+      };
+      const adUnits = [{
+        transactionId: 'au',
+        mediaTypes: {
+          video: {context: 'instream'}
+        }
+      }];
+      const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
+      expect(valid).to.equal(true);
+    });
 
-    const valid = isValidVideoBid({ transactionId: 'au', vastXml: '<xml>vast</xml>' }, {index: stubAuctionIndex({adUnits})});
+    it('catches invalid instream bids', function () {
+      const bid = {
+        transactionId: 'au'
+      };
+      const adUnits = [{
+        transactionId: 'au',
+        mediaTypes: {
+          video: {context: 'instream'}
+        }
+      }];
+      const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
+      expect(valid).to.equal(false);
+    });
 
-    expect(valid).to.equal(false);
-  });
+    it('catches invalid bids when prebid-cache is disabled', function () {
+      const adUnits = [{
+        transactionId: 'au',
+        bidder: 'vastOnlyVideoBidder',
+        mediaTypes: {video: {}},
+      }];
 
-  it('validates valid outstream bids', function () {
-    const bid = {
-      transactionId: 'au',
-      renderer: {
-        url: 'render.url',
-        render: () => true,
-      }
-    };
-    const adUnits = [{
-      transactionId: 'au',
-      mediaTypes: {
-        video: {context: 'outstream'}
-      }
-    }];
-    const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
-    expect(valid).to.equal(true);
-  });
+      const valid = isValidVideoBid({ transactionId: 'au', vastXml: '<xml>vast</xml>' }, {index: stubAuctionIndex({adUnits})});
 
-  it('validates valid outstream bids with a publisher defined renderer', function () {
-    const bid = {
-      transactionId: 'au',
-    };
-    const adUnits = [{
-      transactionId: 'au',
-      mediaTypes: {
-        video: {
-          context: 'outstream',
+      expect(valid).to.equal(false);
+    });
+
+    it('validates valid outstream bids', function () {
+      const bid = {
+        transactionId: 'au',
+        renderer: {
+          url: 'render.url',
+          render: () => true,
         }
-      },
-      renderer: {
-        url: 'render.url',
-        render: () => true,
-      }
-    }];
-    const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
-    expect(valid).to.equal(true);
-  });
+      };
+      const adUnits = [{
+        transactionId: 'au',
+        mediaTypes: {
+          video: {context: 'outstream'}
+        }
+      }];
+      const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
+      expect(valid).to.equal(true);
+    });
 
-  it('catches invalid outstream bids', function () {
-    const bid = {
-      transactionId: 'au',
-    };
-    const adUnits = [{
-      transactionId: 'au',
-      mediaTypes: {
-        video: {context: 'outstream'}
-      }
-    }];
-    const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
-    expect(valid).to.equal(false);
-  });
+    it('validates valid outstream bids with a publisher defined renderer', function () {
+      const bid = {
+        transactionId: 'au',
+      };
+      const adUnits = [{
+        transactionId: 'au',
+        mediaTypes: {
+          video: {
+            context: 'outstream',
+          }
+        },
+        renderer: {
+          url: 'render.url',
+          render: () => true,
+        }
+      }];
+      const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
+      expect(valid).to.equal(true);
+    });
+
+    it('catches invalid outstream bids', function () {
+      const bid = {
+        transactionId: 'au',
+      };
+      const adUnits = [{
+        transactionId: 'au',
+        mediaTypes: {
+          video: {context: 'outstream'}
+        }
+      }];
+      const valid = isValidVideoBid(bid, {index: stubAuctionIndex({adUnits})});
+      expect(valid).to.equal(false);
+    });
+  })
 });