Add LabelScorer base class

src/Flow/Vector.hh

@@ -53,6 +53,8 @@ public:
             : Timestamp(type()), std::vector<T>(n, t) {}
     Vector(const std::vector<T>& v)
             : Timestamp(type()), std::vector<T>(v) {}
+    Vector(const std::vector<T>& v, Time start, Time end)
+            : Timestamp(start, end), std::vector<T>(v) {}
     template<class InputIterator>
     Vector(InputIterator begin, InputIterator end)
             : Timestamp(type()), std::vector<T>(begin, end) {}

src/Nn/LabelScorer/LabelScorer.cc

@@ -0,0 +1,52 @@
+/** Copyright 2024 RWTH Aachen University. All rights reserved.
+ *
+ *  Licensed under the RWTH ASR License (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.hltpr.rwth-aachen.de/rwth-asr/rwth-asr-license.html
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#include "LabelScorer.hh"
+#include <Flow/Timestamp.hh>
+
+namespace Nn {
+
+/*
+ * =============================
+ * === LabelScorer =============
+ * =============================
+ */
+
+LabelScorer::LabelScorer(const Core::Configuration& config)
+        : Core::Component(config) {}
+
+void LabelScorer::addInput(Core::Ref<const Speech::Feature> input) {
+    addInput(Flow::dataPtr(new FeatureVector(*input->mainStream(), input->timestamp().startTime(), input->timestamp().endTime())));
+}
+
+std::optional<LabelScorer::ScoresWithTimes> LabelScorer::getScoresWithTimes(const std::vector<LabelScorer::Request>& requests) {
+    // By default, just loop over the non-batched `getScoreWithTime` and collect the results
+    ScoresWithTimes result;
+
+    result.scores.reserve(requests.size());
+    result.timesteps.reserve(requests.size());
+    for (auto& request : requests) {
+        auto singleResult = getScoreWithTime(request);
+        if (not singleResult.has_value()) {
+            return {};
+        }
+        result.scores.push_back(singleResult->score);
+        result.timesteps.push_back(singleResult->timeframe);
+    }
+
+    return result;
+}
+
+}  // namespace Nn

src/Nn/LabelScorer/LabelScorer.hh

@@ -0,0 +1,144 @@
+/** Copyright 2024 RWTH Aachen University. All rights reserved.
+ *
+ *  Licensed under the RWTH ASR License (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.hltpr.rwth-aachen.de/rwth-asr/rwth-asr-license.html
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#ifndef LABEL_SCORER_HH
+#define LABEL_SCORER_HH
+
+#include <Core/CollapsedVector.hh>
+#include <Core/Component.hh>
+#include <Core/Configuration.hh>
+#include <Core/Parameter.hh>
+#include <Core/ReferenceCounting.hh>
+#include <Core/Types.hh>
+#include <Flow/Timestamp.hh>
+#include <Flow/Vector.hh>
+#include <Mm/FeatureScorer.hh>
+#include <Nn/Types.hh>
+#include <Search/Types.hh>
+#include <Speech/Feature.hh>
+#include <Speech/Types.hh>
+#include <optional>
+#include "ScoringContext.hh"
+
+namespace Nn {
+
+typedef Search::Score                Score;
+typedef Flow::Vector<f32>            FeatureVector;
+typedef Flow::DataPtr<FeatureVector> FeatureVectorRef;
+
+/*
+ * Abstract base class for scoring tokens within an ASR search algorithm.
+ *
+ * This class provides an interface for different types of label scorers in an ASR system.
+ * Label Scorers compute the scores of tokens based on input features and a scoring context.
+ * Children of this base class should represent various ASR model architectures and cover a
+ * wide range of possibilities such as CTC, transducer, AED or other models.
+ *
+ * The usage is intended as follows:
+ *  - Before or during the search, features can be added
+ *  - At the beginning of search, `getInitialScoringContext` should be called
+ *    and used for the first hypotheses
+ *  - For a given hypothesis in search, its search context together with a successor token and
+ *    transition type are packed into a request and scored via `getScoreWithTime`. This also returns
+ *    the timestamp of the successor.
+ *    Note: The scoring function may return no value, in this case it is not ready yet
+ *    and needs more input features.
+ *    Note: There is also the function `getScoresWithTimes` which can handle an entire batch of
+ *    requests at once and might be implemented more efficiently (e.g. using batched model forwarding).
+ *  - For all hypotheses that survive pruning, the LabelScorer can compute a new scoring context
+ *    that extends the previous scoring context of that hypothesis with a given successor token. This new
+ *    scoring context can then be used as context in subsequent search steps.
+ *  - After all features have been passed, the `signalNoMoreFeatures` function is called to inform
+ *    the label scorer that it doesn't need to wait for more features and can score as much as possible.
+ *    This is especially important when the label scorer internally uses an encoder or window with right
+ *    context.
+ *  - When all necessary scores for the current segment have been computed, the `reset` function is called
+ *    to clean up any internal data (e.g. feature buffer) or reset flags of the LabelScorer. Afterwards
+ *    it is ready to receive features for the next segment.
+ *
+ * Each concrete subclass internally implements a concrete type of scoring context which the outside
+ * search algorithm is agnostic to. Depending on the model, this scoring context can consist of things like
+ * the current timestep, a label history, a hidden state or other values.
+ */
+class LabelScorer : public virtual Core::Component,
+                    public Core::ReferenceCounted {
+public:
+    // Transition type as part of scoring or context extension requests
+    enum TransitionType {
+        LABEL_TO_LABEL,
+        LABEL_LOOP,
+        LABEL_TO_BLANK,
+        BLANK_TO_LABEL,
+        BLANK_LOOP,
+    };
+
+    // Request for scoring or context extension
+    struct Request {
+        ScoringContextRef context;
+        LabelIndex        nextToken;
+        TransitionType    transitionType;
+    };
+
+    // Return value of scoring function
+    struct ScoreWithTime {
+        Score                  score;
+        Speech::TimeframeIndex timeframe;
+    };
+
+    // Return value of batched scoring function
+    struct ScoresWithTimes {
+        std::vector<Score>                            scores;
+        Core::CollapsedVector<Speech::TimeframeIndex> timesteps;  // Timesteps vector is internally collapsed  if all timesteps are the same (e.g. time-sync decoding)
+    };
+
+    LabelScorer(const Core::Configuration& config);
+    virtual ~LabelScorer() = default;
+
+    // Prepares the LabelScorer to receive new inputs
+    // e.g. by resetting input buffers and segmentEnd flags
+    virtual void reset() = 0;
+
+    // Tells the LabelScorer that there will be no more input features coming in the current segment
+    virtual void signalNoMoreFeatures() = 0;
+
+    // Gets initial scoring context to use for the hypotheses in the first search step
+    virtual ScoringContextRef getInitialScoringContext() = 0;
+
+    // Creates a copy of the context in the request that is extended using the given token and transition type
+    virtual ScoringContextRef extendedScoringContext(Request request) = 0;
+
+    // Function that returns the mapping of each timeframe index (returned in the scoring functions)
+    // to actual flow timestamps with start-/ and end-time in seconds.
+    virtual const std::vector<Flow::Timestamp>& getTimestamps() const = 0;
+
+    // Add a single input feature
+    virtual void addInput(FeatureVectorRef input) = 0;
+    virtual void addInput(Core::Ref<const Speech::Feature> input);
+
+    // Perform scoring computation for a single request
+    // Return score and timeframe index of the corresponding output
+    // May not return a value if the LabelScorer is not ready to score the request yet
+    // (e.g. not enough features received)
+    virtual std::optional<ScoreWithTime> getScoreWithTime(const Request request) = 0;
+
+    // Perform scoring computation for a batch of requests
+    // May be implemented more efficiently than iterated calls of `getScoreWithTime`
+    // Return two vectors: one vector with scores and one vector with times
+    virtual std::optional<ScoresWithTimes> getScoresWithTimes(const std::vector<Request>& requests);
+};
+
+}  // namespace Nn
+
+#endif  // LABEL_SCORER_HH

src/Nn/LabelScorer/Makefile

@@ -0,0 +1,26 @@
+#!gmake
+
+TOPDIR		= ../../..
+
+include $(TOPDIR)/Makefile.cfg
+
+# -----------------------------------------------------------------------------
+
+SUBDIRS		=
+TARGETS		= libSprintLabelScorer.$(a)
+
+LIBSPRINTLABELSCORER_O =  \
+    $(OBJDIR)/LabelScorer.o \
+    $(OBJDIR)/ScoringContext.o
+
+# -----------------------------------------------------------------------------
+
+all: $(TARGETS)
+
+libSprintLabelScorer.$(a): $(LIBSPRINTLABELSCORER_O)
+	$(MAKELIB) $@ $^
+
+include $(TOPDIR)/Rules.make
+
+sinclude $(LIBSPRINTLABELSCORER_O:.o=.d)
+include $(patsubst %.o,%.d,$(filter %.o,$(CHECK_O)))

src/Nn/LabelScorer/ScoringContext.cc

@@ -0,0 +1,34 @@
+/** Copyright 2024 RWTH Aachen University. All rights reserved.
+ *
+ *  Licensed under the RWTH ASR License (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.hltpr.rwth-aachen.de/rwth-asr/rwth-asr-license.html
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+#include "ScoringContext.hh"
+
+namespace Nn {
+
+typedef Mm::EmissionIndex LabelIndex;
+
+/*
+ * =============================
+ * === ScoringContext ============
+ * =============================
+ */
+size_t ScoringContextHash::operator()(ScoringContextRef history) const {
+    return 0ul;
+}
+
+bool ScoringContextEq::operator()(ScoringContextRef lhs, ScoringContextRef rhs) const {
+    return true;
+}
+
+}  // namespace Nn

src/Nn/LabelScorer/ScoringContext.hh

@@ -0,0 +1,45 @@
+/** Copyright 2024 RWTH Aachen University. All rights reserved.
+ *
+ *  Licensed under the RWTH ASR License (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.hltpr.rwth-aachen.de/rwth-asr/rwth-asr-license.html
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#ifndef SCORING_CONTEXT_HH
+#define SCORING_CONTEXT_HH
+
+#include <Core/ReferenceCounting.hh>
+#include <Mm/Types.hh>
+
+namespace Nn {
+
+typedef Mm::EmissionIndex LabelIndex;
+
+/*
+ * Empty scoring context base class
+ */
+struct ScoringContext : public Core::ReferenceCounted {
+    virtual ~ScoringContext() = default;
+};
+
+typedef Core::Ref<const ScoringContext> ScoringContextRef;
+
+struct ScoringContextHash {
+    size_t operator()(ScoringContextRef history) const;
+};
+
+struct ScoringContextEq {
+    bool operator()(ScoringContextRef lhs, ScoringContextRef rhs) const;
+};
+
+}  // namespace Nn
+
+#endif  // SCORING_CONTEXT_HH

src/Nn/Makefile

@@ -88,6 +88,8 @@ ifdef MODULE_GENERIC_SEQ2SEQ_TREE_SEARCH
   endif
 endif
 
+SUBDIRS += LabelScorer
+
 # -----------------------------------------------------------------------------
 all: $(TARGETS)
 
@@ -99,6 +101,9 @@ interpol:
 libSprintNn.$(a): $(SUBDIRS) $(LIBSPRINTNN_O)
 	$(MAKELIB) $@ $(LIBSPRINTNN_O) $(patsubst %,%/$(OBJDIR)/*.o,$(SUBDIRS))
 
+LabelScorer:
+	$(MAKE) -C $@ libSprintLabelScorer.$(a)
+
 check$(exe): $(CHECK_O)
 	$(LD) $(LD_START_GROUP) $(CHECK_O) $(LD_END_GROUP) -o $@ $(LDFLAGS)