diff --git a/libraries/common/src/main/java/androidx/media3/common/util/CodecSpecificDataUtil.java b/libraries/common/src/main/java/androidx/media3/common/util/CodecSpecificDataUtil.java
index 58d8573f3a..44c42ff85e 100644
--- a/libraries/common/src/main/java/androidx/media3/common/util/CodecSpecificDataUtil.java
+++ b/libraries/common/src/main/java/androidx/media3/common/util/CodecSpecificDataUtil.java
@@ -48,6 +48,8 @@ public final class CodecSpecificDataUtil {
   private static final int RECTANGULAR = 0x00;
 
   // Codecs to constant mappings.
+  // H263
+  private static final String CODEC_ID_H263 = "s263";
   // AVC.
   private static final String CODEC_ID_AVC1 = "avc1";
   private static final String CODEC_ID_AVC2 = "avc2";
@@ -259,6 +261,11 @@ public final class CodecSpecificDataUtil {
     return builder.toString();
   }
 
+  /** Builds an RFC 6381 H263 codec string using profile and level. */
+  public static String buildH263CodecString(int profile, int level) {
+    return Util.formatInvariant("s263.%d.%d", profile, level);
+  }
+
   /**
    * Returns profile and level (as defined by {@link MediaCodecInfo.CodecProfileLevel})
    * corresponding to the codec description string (as defined by RFC 6381) of the given format.
@@ -278,6 +285,8 @@ public final class CodecSpecificDataUtil {
       return getDolbyVisionProfileAndLevel(format.codecs, parts);
     }
     switch (parts[0]) {
+      case CODEC_ID_H263:
+        return getH263ProfileAndLevel(format.codecs, parts);
       case CODEC_ID_AVC1:
       case CODEC_ID_AVC2:
         return getAvcProfileAndLevel(format.codecs, parts);
@@ -463,6 +472,27 @@ public final class CodecSpecificDataUtil {
     return new Pair<>(profile, level);
   }
 
+  /** Returns H263 profile and level from codec string. */
+  private static Pair<Integer, Integer> getH263ProfileAndLevel(String codec, String[] parts) {
+    Pair<Integer, Integer> defaultProfileAndLevel =
+        new Pair<>(
+            MediaCodecInfo.CodecProfileLevel.H263ProfileBaseline,
+            MediaCodecInfo.CodecProfileLevel.H263Level10);
+    if (parts.length < 3) {
+      Log.w(TAG, "Ignoring malformed H263 codec string: " + codec);
+      return defaultProfileAndLevel;
+    }
+
+    try {
+      int profile = Integer.parseInt(parts[1]);
+      int level = Integer.parseInt(parts[2]);
+      return new Pair<>(profile, level);
+    } catch (NumberFormatException e) {
+      Log.w(TAG, "Ignoring malformed H263 codec string: " + codec);
+      return defaultProfileAndLevel;
+    }
+  }
+
   @Nullable
   private static Pair<Integer, Integer> getAvcProfileAndLevel(String codec, String[] parts) {
     if (parts.length < 2) {
diff --git a/libraries/common/src/main/java/androidx/media3/common/util/MediaFormatUtil.java b/libraries/common/src/main/java/androidx/media3/common/util/MediaFormatUtil.java
index 1824b33f2d..f90f4ccc51 100644
--- a/libraries/common/src/main/java/androidx/media3/common/util/MediaFormatUtil.java
+++ b/libraries/common/src/main/java/androidx/media3/common/util/MediaFormatUtil.java
@@ -28,6 +28,7 @@ import androidx.media3.common.MimeTypes;
 import com.google.common.collect.ImmutableList;
 import java.nio.ByteBuffer;
 import java.util.List;
+import java.util.Objects;
 
 /** Helper class containing utility methods for managing {@link MediaFormat} instances. */
 @UnstableApi
@@ -79,7 +80,7 @@ public final class MediaFormatUtil {
             .setAverageBitrate(
                 getInteger(
                     mediaFormat, MediaFormat.KEY_BIT_RATE, /* defaultValue= */ Format.NO_VALUE))
-            .setCodecs(mediaFormat.getString(MediaFormat.KEY_CODECS_STRING))
+            .setCodecs(getCodecString(mediaFormat))
             .setFrameRate(getFrameRate(mediaFormat, /* defaultValue= */ Format.NO_VALUE))
             .setWidth(
                 getInteger(mediaFormat, MediaFormat.KEY_WIDTH, /* defaultValue= */ Format.NO_VALUE))
@@ -332,6 +333,32 @@ public final class MediaFormatUtil {
     return mediaFormat.containsKey(name) ? mediaFormat.getFloat(name) : defaultValue;
   }
 
+  /** Supports {@link MediaFormat#getString(String, String)} for {@code API < 29}. */
+  @Nullable
+  public static String getString(
+      MediaFormat mediaFormat, String name, @Nullable String defaultValue) {
+    return mediaFormat.containsKey(name) ? mediaFormat.getString(name) : defaultValue;
+  }
+
+  /**
+   * Returns a {@code Codecs string} of {@link MediaFormat}. In case of an H263 codec string, builds
+   * and returns an RFC 6381 H263 codec string using profile and level.
+   */
+  @Nullable
+  @SuppressLint("InlinedApi") // Inlined MediaFormat keys.
+  private static String getCodecString(MediaFormat mediaFormat) {
+    // Add H263 profile and level to codec string as per RFC 6381.
+    if (Objects.equals(mediaFormat.getString(MediaFormat.KEY_MIME), MimeTypes.VIDEO_H263)
+        && mediaFormat.containsKey(MediaFormat.KEY_PROFILE)
+        && mediaFormat.containsKey(MediaFormat.KEY_LEVEL)) {
+      return CodecSpecificDataUtil.buildH263CodecString(
+          mediaFormat.getInteger(MediaFormat.KEY_PROFILE),
+          mediaFormat.getInteger(MediaFormat.KEY_LEVEL));
+    } else {
+      return getString(mediaFormat, MediaFormat.KEY_CODECS_STRING, /* defaultValue= */ null);
+    }
+  }
+
   /**
    * Returns the frame rate from a {@link MediaFormat}.
    *
diff --git a/libraries/common/src/test/java/androidx/media3/common/util/CodecSpecificDataUtilTest.java b/libraries/common/src/test/java/androidx/media3/common/util/CodecSpecificDataUtilTest.java
index 74c98fd882..4708f05d21 100644
--- a/libraries/common/src/test/java/androidx/media3/common/util/CodecSpecificDataUtilTest.java
+++ b/libraries/common/src/test/java/androidx/media3/common/util/CodecSpecificDataUtilTest.java
@@ -53,6 +53,15 @@ public class CodecSpecificDataUtilTest {
     assertThat(sampleRateAndChannelCount.second).isEqualTo(2);
   }
 
+  @Test
+  public void getCodecProfileAndLevel_handlesH263CodecString() {
+    assertCodecProfileAndLevelForCodecsString(
+        MimeTypes.VIDEO_H263,
+        "s263.1.1",
+        MediaCodecInfo.CodecProfileLevel.H263ProfileBaseline,
+        MediaCodecInfo.CodecProfileLevel.H263Level10);
+  }
+
   @Test
   public void getCodecProfileAndLevel_handlesVp9Profile1CodecString() {
     assertCodecProfileAndLevelForCodecsString(
diff --git a/libraries/muxer/src/main/java/androidx/media3/muxer/Boxes.java b/libraries/muxer/src/main/java/androidx/media3/muxer/Boxes.java
index 0480bca848..55cb2c2b12 100644
--- a/libraries/muxer/src/main/java/androidx/media3/muxer/Boxes.java
+++ b/libraries/muxer/src/main/java/androidx/media3/muxer/Boxes.java
@@ -26,11 +26,14 @@ import static java.nio.charset.StandardCharsets.UTF_8;
 
 import android.media.MediaCodec;
 import android.media.MediaCodec.BufferInfo;
+import android.media.MediaCodecInfo;
+import android.util.Pair;
 import androidx.annotation.Nullable;
 import androidx.media3.common.C;
 import androidx.media3.common.ColorInfo;
 import androidx.media3.common.Format;
 import androidx.media3.common.MimeTypes;
+import androidx.media3.common.util.CodecSpecificDataUtil;
 import androidx.media3.common.util.Util;
 import androidx.media3.container.MdtaMetadataEntry;
 import androidx.media3.container.Mp4LocationData;
@@ -678,7 +681,7 @@ import org.checkerframework.checker.nullness.qual.PolyNull;
       case MimeTypes.AUDIO_OPUS:
         return dOpsBox(format);
       case MimeTypes.VIDEO_H263:
-        return d263Box();
+        return d263Box(format);
       case MimeTypes.VIDEO_H264:
         return avcCBox(format);
       case MimeTypes.VIDEO_H265:
@@ -1258,13 +1261,19 @@ import org.checkerframework.checker.nullness.qual.PolyNull;
   }
 
   /** Returns the d263Box box as per 3GPP ETSI TS 126 244: 6.8. */
-  private static ByteBuffer d263Box() {
+  private static ByteBuffer d263Box(Format format) {
     ByteBuffer d263Box = ByteBuffer.allocate(7);
     d263Box.put("    ".getBytes(UTF_8)); // 4 spaces (vendor)
-    d263Box.put((byte) 0x0); // decoder version
-    // TODO: b/352000778 - Get profile and level from format.
-    d263Box.put((byte) 0x10); // level
-    d263Box.put((byte) 0x0); // profile
+    d263Box.put((byte) 0x00); // decoder version
+    Pair<Integer, Integer> profileAndLevel = CodecSpecificDataUtil.getCodecProfileAndLevel(format);
+    if (profileAndLevel == null) {
+      profileAndLevel =
+          new Pair<>(
+              MediaCodecInfo.CodecProfileLevel.H263ProfileBaseline,
+              MediaCodecInfo.CodecProfileLevel.H263Level10);
+    }
+    d263Box.put(profileAndLevel.second.byteValue()); // level
+    d263Box.put(profileAndLevel.first.byteValue()); // profile
 
     d263Box.flip();
     return BoxUtils.wrapIntoBox("d263", d263Box);
diff --git a/libraries/muxer/src/test/java/androidx/media3/muxer/BoxesTest.java b/libraries/muxer/src/test/java/androidx/media3/muxer/BoxesTest.java
index e98f16b6cb..f137ce66fd 100644
--- a/libraries/muxer/src/test/java/androidx/media3/muxer/BoxesTest.java
+++ b/libraries/muxer/src/test/java/androidx/media3/muxer/BoxesTest.java
@@ -368,7 +368,12 @@ public class BoxesTest {
 
   @Test
   public void createVideoSampleEntryBox_forH263_matchesExpected() throws Exception {
-    Format format = FAKE_VIDEO_FORMAT.buildUpon().setSampleMimeType(MimeTypes.VIDEO_H263).build();
+    Format format =
+        FAKE_VIDEO_FORMAT
+            .buildUpon()
+            .setSampleMimeType(MimeTypes.VIDEO_H263)
+            .setCodecs("s263.1.10")
+            .build();
 
     ByteBuffer videoSampleEntryBox = Boxes.videoSampleEntry(format);
 
diff --git a/libraries/test_data/src/test/assets/muxerdumps/video_sample_entry_box_h263.dump b/libraries/test_data/src/test/assets/muxerdumps/video_sample_entry_box_h263.dump
index 2af4e7ea7e..8718495755 100644
--- a/libraries/test_data/src/test/assets/muxerdumps/video_sample_entry_box_h263.dump
+++ b/libraries/test_data/src/test/assets/muxerdumps/video_sample_entry_box_h263.dump
@@ -1,2 +1,2 @@
 s263 (117 bytes):
-  Data = length 109, hash EABCBA75
+  Data = length 109, hash 9FFB4BBC