diff --git a/core/src/main/java/eu/ostrzyciel/jelly/core/EncoderLookup.java b/core/src/main/java/eu/ostrzyciel/jelly/core/EncoderLookup.java
index cfebf1c..0f824ee 100644
--- a/core/src/main/java/eu/ostrzyciel/jelly/core/EncoderLookup.java
+++ b/core/src/main/java/eu/ostrzyciel/jelly/core/EncoderLookup.java
@@ -1,5 +1,6 @@
 package eu.ostrzyciel.jelly.core;
 
+import java.util.Arrays;
 import java.util.HashMap;
 
 /**
@@ -158,4 +159,16 @@ public LookupEntry getOrAddEntry(String key) {
         entryForReturns.getId = id;
         return entryForReturns;
     }
+
+    public void clear() {
+        map.clear();
+        Arrays.fill(table, 0);
+        tail = 0;
+        used = 0;
+        lastSetId = -1000;
+        if (useSerials) {
+            Arrays.fill(serials, 0);
+            serials[0] = -1;
+        }
+    }
 }
diff --git a/core/src/main/java/eu/ostrzyciel/jelly/core/TranscoderLookup.java b/core/src/main/java/eu/ostrzyciel/jelly/core/TranscoderLookup.java
new file mode 100644
index 0000000..764caba
--- /dev/null
+++ b/core/src/main/java/eu/ostrzyciel/jelly/core/TranscoderLookup.java
@@ -0,0 +1,81 @@
+package eu.ostrzyciel.jelly.core;
+
+class TranscoderLookup {
+    private final int outputSize;
+    private int[] table;
+    private final EncoderLookup lookup;
+
+    // 0-compression:
+    //  - for prefixes and datatypes: no worries about splicing, because zeroes are not allowed at the start of the
+    //    stream. While splitting, we need to check for zeroes at the start of the stream and remap them.
+    //  - IRI names: remap all 0s forcefully
+    private final boolean isNameLookup;
+    private boolean isFirstElement = true;
+    private int lastSetId = 0;
+    private int lastInputGetId = 0;
+    private int lastOutputGetId = 0;
+
+    TranscoderLookup(boolean isNameLookup, int outputSize) {
+        this.isNameLookup = isNameLookup;
+        this.outputSize = outputSize;
+        this.lookup = new EncoderLookup(outputSize, false);
+    }
+
+    EncoderLookup.LookupEntry addEntry(int originalId, String value) {
+        if (originalId == 0) {
+            originalId = ++lastSetId;
+        } else {
+            lastSetId = originalId;
+        }
+        EncoderLookup.LookupEntry entry = lookup.getOrAddEntry(value);
+        table[originalId] = entry.getId;
+        return entry;
+    }
+
+    int remap(int id) {
+        if (isNameLookup) {
+            if (id == 0) {
+                if (isFirstElement) {
+                    lastInputGetId = id = 1;
+                } else {
+                    id = ++lastInputGetId;
+                }
+            } else {
+                lastInputGetId = id;
+            }
+            isFirstElement = false;
+            int outputId = table[id];
+            lookup.onAccess(outputId);
+            if (outputId == lastOutputGetId + 1) {
+                lastOutputGetId++;
+                return 0;
+            }
+            lastOutputGetId = outputId;
+            return outputId;
+        }
+        if (id == 0) {
+            // No need to do onAccess here, because this is the same as the last element
+            if (isFirstElement) {
+                // We are starting a new output stream, so we need to remap the first zero.
+                isFirstElement = false;
+                return lastInputGetId;
+            }
+            return 0;
+        }
+        lastInputGetId = id;
+        id = table[id];
+        lookup.onAccess(id);
+        isFirstElement = false;
+        return id;
+    }
+
+    void newInputStream(int size) {
+        if (size > outputSize) {
+            throw new IllegalArgumentException("Input lookup size cannot be greater than the output lookup size");
+        }
+        if (table == null || table.length < size + 1) {
+            table = new int[size + 1];
+        }
+        isFirstElement = true;
+    }
+}
diff --git a/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoEncoder.scala b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoEncoder.scala
index 3669426..8fe7bc3 100644
--- a/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoEncoder.scala
+++ b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoEncoder.scala
@@ -2,7 +2,7 @@ package eu.ostrzyciel.jelly.core
 
 import eu.ostrzyciel.jelly.core.proto.v1.*
 
-import scala.collection.mutable.{ArrayBuffer, ListBuffer}
+import scala.collection.mutable.ArrayBuffer
 
 object ProtoEncoder:
   private val graphEnd = Seq(RdfStreamRow(RdfGraphEnd.defaultInstance))
@@ -149,12 +149,12 @@ abstract class ProtoEncoder[TNode, -TTriple, -TQuad, -TQuoted](val options: RdfS
     options.maxNameTableSize,
     Math.max(Math.min(options.maxNameTableSize, 1024), 256),
   )
-  private var emittedOptions = false
+  private var emittedOptions: Boolean = false
 
   private val lastSubject: LastNodeHolder[TNode] = new LastNodeHolder()
   private val lastPredicate: LastNodeHolder[TNode] = new LastNodeHolder()
   private val lastObject: LastNodeHolder[TNode] = new LastNodeHolder()
-  private var lastGraph: TNode | LastNodeHolder.NoValue.type = LastNodeHolder.NoValue 
+  private var lastGraph: TNode | LastNodeHolder.NoValue.type = LastNodeHolder.NoValue
 
   private def nodeToProtoWrapped(node: TNode, lastNodeHolder: LastNodeHolder[TNode]): SpoTerm =
     if node.equals(lastNodeHolder.node) then null
diff --git a/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoder.scala b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoder.scala
new file mode 100644
index 0000000..5478591
--- /dev/null
+++ b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoder.scala
@@ -0,0 +1,17 @@
+package eu.ostrzyciel.jelly.core
+
+import eu.ostrzyciel.jelly.core.JellyOptions
+import eu.ostrzyciel.jelly.core.proto.v1.*
+
+object ProtoTranscoder:
+  def fastMergingTranscoderUnsafe(outputOptions: RdfStreamOptions): ProtoTranscoder =
+    ProtoTranscoderImpl(None, outputOptions)
+
+  def fastMergingTranscoder(
+    supportedInputOptions: RdfStreamOptions, outputOptions: RdfStreamOptions
+  ): ProtoTranscoder = ProtoTranscoderImpl(Some(supportedInputOptions), outputOptions)
+
+trait ProtoTranscoder:
+  def ingestRow(row: RdfStreamRow): Iterable[RdfStreamRow]
+
+  def ingestFrame(frame: RdfStreamFrame): RdfStreamFrame
diff --git a/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderImpl.scala b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderImpl.scala
new file mode 100644
index 0000000..d4a4f73
--- /dev/null
+++ b/core/src/main/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderImpl.scala
@@ -0,0 +1,155 @@
+package eu.ostrzyciel.jelly.core
+
+import eu.ostrzyciel.jelly.core.JellyExceptions.RdfProtoDeserializationError
+import eu.ostrzyciel.jelly.core.proto.v1.*
+
+import scala.annotation.switch
+import scala.collection.mutable.ArrayBuffer
+
+// Note: the caller is responsible for setting a physical stream type in the output!
+
+private final class ProtoTranscoderImpl(
+  supportedInputOptions: Option[RdfStreamOptions],
+  outputOptions: RdfStreamOptions
+) extends ProtoTranscoder:
+  override def ingestRow(row: RdfStreamRow): Iterable[RdfStreamRow] =
+    rowBuffer.clear()
+    processRow(row)
+    rowBuffer.toSeq
+
+  override def ingestFrame(frame: RdfStreamFrame): RdfStreamFrame =
+    rowBuffer.clear()
+    for row <- frame.rows do
+      processRow(row)
+    val newFrame = RdfStreamFrame(rowBuffer.toSeq)
+    newFrame
+
+  // Transcoder state
+  private val checkInputOptions = supportedInputOptions.isDefined
+  private val prefixLookup: TranscoderLookup = new TranscoderLookup(false, outputOptions.maxPrefixTableSize)
+  private val nameLookup: TranscoderLookup = new TranscoderLookup(true, outputOptions.maxNameTableSize)
+  private val datatypeLookup: TranscoderLookup = new TranscoderLookup(false, outputOptions.maxDatatypeTableSize)
+
+  // Current input stream state
+  private var inputOptions: RdfStreamOptions = null
+  private var inputUsesPrefixes = false
+
+  // Current output stream state
+  private val rowBuffer = new ArrayBuffer[RdfStreamRow](128)
+  private var changeInTerms = false
+  private var emittedOptions = false
+
+  private def processRow(row: RdfStreamRow): Unit =
+    val r = row.row
+    if r == null then
+      throw new RdfProtoDeserializationError("Row kind is not set.")
+    (r.streamRowValueNumber: @switch) match
+      case RdfStreamRow.OPTIONS_FIELD_NUMBER => handleOptions(r.options)
+      case RdfStreamRow.TRIPLE_FIELD_NUMBER => handleTriple(row)
+      case RdfStreamRow.QUAD_FIELD_NUMBER => handleQuad(row)
+      case RdfStreamRow.GRAPH_START_FIELD_NUMBER =>
+      case RdfStreamRow.GRAPH_END_FIELD_NUMBER => rowBuffer.append(row)
+      case RdfStreamRow.NAME_FIELD_NUMBER =>
+        val name = r.name
+        val entry = nameLookup.addEntry(name.id, name.value)
+        if !entry.newEntry then ()
+        else if entry.setId == name.id then rowBuffer.append(row)
+        else rowBuffer.append(RdfStreamRow(RdfNameEntry(entry.setId, name.value)))
+      case RdfStreamRow.PREFIX_FIELD_NUMBER =>
+        val prefix = r.prefix
+        val entry = prefixLookup.addEntry(prefix.id, prefix.value)
+        if !entry.newEntry then ()
+        else if entry.setId == prefix.id then rowBuffer.append(row)
+        else rowBuffer.append(RdfStreamRow(RdfPrefixEntry(entry.setId, prefix.value)))
+      case RdfStreamRow.DATATYPE_FIELD_NUMBER =>
+        val datatype = r.datatype
+        val entry = datatypeLookup.addEntry(datatype.id, datatype.value)
+        if !entry.newEntry then ()
+        else if entry.setId == datatype.id then rowBuffer.append(row)
+        else rowBuffer.append(RdfStreamRow(RdfDatatypeEntry(entry.setId, datatype.value)))
+      case _ =>
+        // This case should never happen
+        throw new RdfProtoDeserializationError("Row kind is not set.")
+
+  private def handleTriple(row: RdfStreamRow): Unit =
+    this.changeInTerms = false
+    val triple = row.row.triple
+    val s1 = handleSpoTerm(triple.subject)
+    val p1 = handleSpoTerm(triple.predicate)
+    val o1 = handleSpoTerm(triple.`object`)
+    if changeInTerms then
+      rowBuffer.append(RdfStreamRow(RdfTriple(s1, p1, o1)))
+    else rowBuffer.append(row)
+
+  private def handleQuad(row: RdfStreamRow): Unit =
+    this.changeInTerms = false
+    val quad = row.row.quad
+    val s1 = handleSpoTerm(quad.subject)
+    val p1 = handleSpoTerm(quad.predicate)
+    val o1 = handleSpoTerm(quad.`object`)
+    val g1 = handleGraphTerm(quad.graph)
+    if changeInTerms then
+      rowBuffer.append(RdfStreamRow(RdfQuad(s1, p1, o1, g1)))
+    else rowBuffer.append(row)
+
+  private def handleSpoTerm(term: SpoTerm): SpoTerm =
+    if term == null then null
+    else if term.isIri then handleIri(term.iri)
+    else if term.isBnode then term
+    else if term.isLiteral then handleLiteral(term.literal)
+    else if term.isTripleTerm then handleTripleTerm(term.tripleTerm)
+    else throw new RdfProtoDeserializationError("Unknown term type.")
+
+  private def handleGraphTerm(term: GraphTerm): GraphTerm =
+    if term == null then null
+    else if term.isIri then handleIri(term.iri)
+    else if term.isDefaultGraph then term
+    else if term.isBnode then term
+    else if term.isLiteral then handleLiteral(term.literal)
+    else throw new RdfProtoDeserializationError("Unknown term type.")
+
+  private def handleIri(iri: RdfIri): RdfIri =
+    val prefix = iri.prefixId
+    val name = iri.nameId
+    val prefix1 = if inputUsesPrefixes then prefixLookup.remap(prefix) else 0
+    val name1 = nameLookup.remap(name)
+    if prefix1 != prefix || name1 != name then
+      changeInTerms = true
+      RdfIri(prefix1, name1)
+    else iri
+
+  private def handleLiteral(literal: RdfLiteral): RdfLiteral =
+    if !literal.literalKind.isDatatype then literal
+    else
+      val dt = literal.literalKind.datatype
+      val dt1 = datatypeLookup.remap(dt)
+      if dt1 != dt then
+        changeInTerms = true
+        RdfLiteral(literal.lex, RdfLiteral.LiteralKind.Datatype(dt1))
+      else literal
+
+  private def handleTripleTerm(triple: RdfTriple): RdfTriple =
+    val s1 = handleSpoTerm(triple.subject)
+    val p1 = handleSpoTerm(triple.predicate)
+    val o1 = handleSpoTerm(triple.`object`)
+    if s1 != triple.subject || p1 != triple.predicate || o1 != triple.`object` then
+      changeInTerms = true
+      RdfTriple(s1, p1, o1)
+    else triple
+
+  private def handleOptions(options: RdfStreamOptions): Unit =
+    if checkInputOptions then
+      // TODO: check if this is the same physical stream type...
+      JellyOptions.checkCompatibility(options, supportedInputOptions.get)
+    this.inputUsesPrefixes = options.maxPrefixTableSize > 0
+    if inputUsesPrefixes then
+      prefixLookup.newInputStream(options.maxPrefixTableSize)
+    nameLookup.newInputStream(options.maxNameTableSize)
+    datatypeLookup.newInputStream(options.maxDatatypeTableSize)
+    // Update the input options
+    inputOptions = options
+    if !emittedOptions then
+      emittedOptions = true
+      rowBuffer.append(RdfStreamRow(outputOptions.copy(
+        version = Constants.protoVersion
+      )))
diff --git a/core/src/test/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderSpec.scala b/core/src/test/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderSpec.scala
new file mode 100644
index 0000000..77cc46f
--- /dev/null
+++ b/core/src/test/scala/eu/ostrzyciel/jelly/core/ProtoTranscoderSpec.scala
@@ -0,0 +1,67 @@
+package eu.ostrzyciel.jelly.core
+
+import eu.ostrzyciel.jelly.core.ProtoTestCases.*
+import eu.ostrzyciel.jelly.core.helpers.{MockConverterFactory, Mrl}
+import eu.ostrzyciel.jelly.core.proto.v1.*
+import org.scalatest.Inspectors
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+
+class ProtoTranscoderSpec extends AnyWordSpec, Inspectors, Matchers:
+  def smallOptions(prefixTableSize: Int) = RdfStreamOptions(
+    maxNameTableSize = 4,
+    maxPrefixTableSize = prefixTableSize,
+    maxDatatypeTableSize = 8,
+  )
+
+  "ProtoTranscoder" should {
+    "splice two identical streams" when {
+      "input is Triples1" in {
+        // TODO: more cases
+        val options: RdfStreamOptions = JellyOptions.smallAllFeatures.withPhysicalType(PhysicalStreamType.TRIPLES)
+        val input: RdfStreamFrame = Triples1.encodedFull(options, 100).head
+        val transcoder = ProtoTranscoder.fastMergingTranscoderUnsafe(options)
+        // First frame should be returned as is
+        val out1 = transcoder.ingestFrame(input)
+        out1 shouldBe input
+        // What's more, the rows should be the exact same objects (except the options)
+        forAll(input.rows.zip(out1.rows).drop(1)) { case (in, out) =>
+          in eq out shouldBe true // reference equality
+        }
+
+        val out2 = transcoder.ingestFrame(input)
+        out2.rows.size shouldBe < (input.rows.size)
+        // No row in out2 should be an options row or a lookup entry row
+        forAll(out2.rows) { (row: RdfStreamRow) =>
+          row.row.isOptions shouldBe false
+          row.row.isPrefix shouldBe false
+          row.row.isName shouldBe false
+          row.row.isDatatype shouldBe false
+        }
+
+        // If there is a row in out2 with same content as in input, it should be the same object
+        var identicalRows = 0
+        forAll(input.rows) { (row: RdfStreamRow) =>
+          val sameRow = out2.rows.find(_.row == row.row)
+          if (sameRow.isDefined) {
+            sameRow.get eq row shouldBe true
+            identicalRows += 1
+          }
+        }
+        // Something should be identical
+        identicalRows shouldBe > (0)
+
+        // Decode the output
+        val decoder = MockConverterFactory.anyStatementDecoder(None)
+        val statements1 = out1.rows.flatMap(decoder.ingestRow)
+        val statements2 = out2.rows.flatMap(decoder.ingestRow)
+        statements1 shouldBe statements2
+      }
+    }
+
+    // TODO: same, with more repetitions
+
+    // TODO: splicing multiple different streams in various orders
+
+    // TODO: exception handling
+  }
\ No newline at end of file
diff --git a/core/src/test/scala/eu/ostrzyciel/jelly/core/TranscoderLookupSpec.scala b/core/src/test/scala/eu/ostrzyciel/jelly/core/TranscoderLookupSpec.scala
new file mode 100644
index 0000000..c7b50be
--- /dev/null
+++ b/core/src/test/scala/eu/ostrzyciel/jelly/core/TranscoderLookupSpec.scala
@@ -0,0 +1,122 @@
+package eu.ostrzyciel.jelly.core
+
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+
+class TranscoderLookupSpec extends AnyWordSpec, Matchers:
+  import EncoderLookup.LookupEntry
+
+  "TranscoderLookup" should {
+    "throw an exception when trying to set input lookup size greater than the output" in {
+      val tl = TranscoderLookup(false, 100)
+      val ex = intercept[IllegalArgumentException] {
+        tl.newInputStream(120)
+      }
+      ex.getMessage should include ("Input lookup size cannot be greater than the output lookup size")
+    }
+
+    "remap IDs" when {
+      "it's a prefix lookup" in {
+        val tl = TranscoderLookup(false, 120)
+        tl.newInputStream(100)
+        tl.addEntry(80, "s80").getId shouldBe 1
+        tl.addEntry(81, "s81").getId shouldBe 2
+
+        tl.remap(80) shouldBe 1
+        tl.remap(0) shouldBe 0
+        tl.remap(0) shouldBe 0
+        tl.remap(81) shouldBe 2
+        tl.remap(80) shouldBe 1
+        tl.remap(81) shouldBe 2
+        tl.remap(0) shouldBe 0
+      }
+
+      "it's a name lookup" in {
+        val tl = TranscoderLookup(true, 100)
+        tl.newInputStream(100)
+        tl.addEntry(80, "s80").getId shouldBe 1
+        tl.addEntry(81, "s81").getId shouldBe 2
+        tl.addEntry(82, "s82").getId shouldBe 3
+        tl.addEntry(83, "s83").getId shouldBe 4
+
+        tl.remap(80) shouldBe 0
+        tl.remap(80) shouldBe 1
+        tl.remap(80) shouldBe 1
+        tl.remap(81) shouldBe 0
+        tl.remap(82) shouldBe 0
+        tl.remap(82) shouldBe 3
+        tl.remap(83) shouldBe 0
+
+        // and with 0 in the input
+        tl.remap(80) shouldBe 1
+        tl.remap(0) shouldBe 0
+        tl.remap(0) shouldBe 0
+        tl.remap(80) shouldBe 1
+      }
+    }
+
+    "remap IDs evicting old entries" when {
+      "it's a prefix lookup" in {
+        val tl = TranscoderLookup(false, 10)
+        tl.newInputStream(5)
+        for i <- 0 to 50 do
+          tl.addEntry((i % 5) + 1, s"s$i").getId shouldBe (i % 10) + 1
+          tl.remap((i % 5) + 1) shouldBe (i % 10) + 1
+      }
+
+      "it's a name lookup" in {
+        val tl = TranscoderLookup(true, 10)
+        tl.newInputStream(5)
+        for i <- 0 to 50 do
+          tl.addEntry((i % 5) + 1, s"s$i").getId shouldBe (i % 10) + 1
+          if (i % 10) != 0 || i == 0 then
+            tl.remap((i % 5) + 1) shouldBe 0
+          else
+            tl.remap((i % 5) + 1) shouldBe (i % 10) + 1
+      }
+    }
+
+    "decode 0-encoding in lookup entries in the input stream" when {
+      "it's a prefix lookup" in {
+        val tl = TranscoderLookup(false, 10)
+        tl.newInputStream(5)
+        tl.addEntry(0, "s1_1")
+        tl.addEntry(0, "s2_1")
+        tl.addEntry(0, "s3_1")
+        tl.remap(1) shouldBe 1
+
+        tl.addEntry(1, "s1_2")
+        tl.remap(1) shouldBe 4
+        tl.remap(2) shouldBe 2
+        tl.remap(3) shouldBe 3
+        tl.remap(0) shouldBe 0
+
+        // Recover an entry
+        tl.addEntry(5, "s1_1")
+        tl.remap(5) shouldBe 1
+        tl.remap(0) shouldBe 0
+      }
+
+      "it's a name lookup" in {
+        val tl = TranscoderLookup(true, 10)
+        tl.newInputStream(5)
+        tl.addEntry(0, "s1_1")
+        tl.addEntry(0, "s2_1")
+        tl.addEntry(0, "s3_1")
+        tl.remap(1) shouldBe 0
+
+        tl.addEntry(1, "s1_2")
+        tl.remap(1) shouldBe 4
+        tl.remap(0) shouldBe 2
+        tl.remap(0) shouldBe 0
+
+        // Recover an entry
+        tl.addEntry(5, "s1_1")
+        tl.remap(5) shouldBe 1
+        tl.remap(2) shouldBe 0
+      }
+    }
+
+    // TODO: cases for isFirstElement
+  }
+