diff --git a/src/media-sink.ts b/src/media-sink.ts
index 179b024..b94a38f 100644
--- a/src/media-sink.ts
+++ b/src/media-sink.ts
@@ -201,9 +201,10 @@ export class EncodedPacketSink {
 		}
 
 		const packet = await this._track._backing.getKeyPacket(timestamp, options);
-		if (!packet || packet.type === 'delta') {
+		if (!packet) {
 			return packet;
 		}
+		assert(packet.type === 'key');
 
 		const determinedType = await this._track.determinePacketType(packet);
 		if (determinedType === 'delta') {
@@ -235,9 +236,10 @@ export class EncodedPacketSink {
 		}
 
 		const nextPacket = await this._track._backing.getNextKeyPacket(packet, options);
-		if (!nextPacket || nextPacket.type === 'delta') {
+		if (!nextPacket) {
 			return nextPacket;
 		}
+		assert(nextPacket.type === 'key');
 
 		const determinedType = await this._track.determinePacketType(nextPacket);
 		if (determinedType === 'delta') {
@@ -474,9 +476,6 @@ export abstract class BaseMediaSampleSink<
 			const packetSink = this._createPacketSink();
 			const keyPacket = await packetSink.getKeyPacket(startTimestamp, { verifyKeyPackets: true })
 				?? await packetSink.getFirstPacket();
-			if (!keyPacket) {
-				return;
-			}
 
 			let currentPacket: EncodedPacket | null = keyPacket;
 
@@ -498,7 +497,7 @@ export abstract class BaseMediaSampleSink<
 				}
 			}
 
-			const packets = packetSink.packets(keyPacket, endPacket);
+			const packets = packetSink.packets(keyPacket ?? undefined, endPacket);
 			await packets.next(); // Skip the start packet as we already have it
 
 			while (currentPacket && !ended && !this._track.input._disposed) {