Allow num_frames and duration to be absent in C++ decoder (#708)

Author: scotts

src/torchcodec/_core/SingleStreamDecoder.cpp

@@ -602,16 +602,22 @@ FrameBatchOutput SingleStreamDecoder::getFramesInRange(
   const auto& streamMetadata =
       containerMetadata_.allStreamMetadata[activeStreamIndex_];
   const auto& streamInfo = streamInfos_[activeStreamIndex_];
-  int64_t numFrames = getNumFrames(streamMetadata);
   TORCH_CHECK(
       start >= 0, "Range start, " + std::to_string(start) + " is less than 0.");
-  TORCH_CHECK(
-      stop <= numFrames,
-      "Range stop, " + std::to_string(stop) +
-          ", is more than the number of frames, " + std::to_string(numFrames));
   TORCH_CHECK(
       step > 0, "Step must be greater than 0; is " + std::to_string(step));
 
+  // Note that if we do not have the number of frames available in our metadata,
+  // then we assume that the upper part of the range is valid.
+  std::optional<int64_t> numFrames = getNumFrames(streamMetadata);
+  if (numFrames.has_value()) {
+    TORCH_CHECK(
+        stop <= numFrames.value(),
+        "Range stop, " + std::to_string(stop) +
+            ", is more than the number of frames, " +
+            std::to_string(numFrames.value()));
+  }
+
   int64_t numOutputFrames = std::ceil((stop - start) / double(step));
   const auto& videoStreamOptions = streamInfo.videoStreamOptions;
   FrameBatchOutput frameBatchOutput(
@@ -676,7 +682,7 @@ FrameBatchOutput SingleStreamDecoder::getFramesPlayedAt(
       containerMetadata_.allStreamMetadata[activeStreamIndex_];
 
   double minSeconds = getMinSeconds(streamMetadata);
-  double maxSeconds = getMaxSeconds(streamMetadata);
+  std::optional<double> maxSeconds = getMaxSeconds(streamMetadata);
 
   // The frame played at timestamp t and the one played at timestamp `t +
   // eps` are probably the same frame, with the same index. The easiest way to
@@ -687,10 +693,20 @@ FrameBatchOutput SingleStreamDecoder::getFramesPlayedAt(
   for (size_t i = 0; i < timestamps.size(); ++i) {
     auto frameSeconds = timestamps[i];
     TORCH_CHECK(
-        frameSeconds >= minSeconds && frameSeconds < maxSeconds,
+        frameSeconds >= minSeconds,
         "frame pts is " + std::to_string(frameSeconds) +
-            "; must be in range [" + std::to_string(minSeconds) + ", " +
-            std::to_string(maxSeconds) + ").");
+            "; must be greater than or equal to " + std::to_string(minSeconds) +
+            ".");
+
+    // Note that if we can't determine the maximum number of seconds from the
+    // metadata, then we assume the frame's pts is valid.
+    if (maxSeconds.has_value()) {
+      TORCH_CHECK(
+          frameSeconds < maxSeconds.value(),
+          "frame pts is " + std::to_string(frameSeconds) +
+              "; must be less than " + std::to_string(maxSeconds.value()) +
+              ".");
+    }
 
     frameIndices[i] = secondsToIndexLowerBound(frameSeconds);
   }
@@ -737,17 +753,26 @@ FrameBatchOutput SingleStreamDecoder::getFramesPlayedInRange(
   }
 
   double minSeconds = getMinSeconds(streamMetadata);
-  double maxSeconds = getMaxSeconds(streamMetadata);
   TORCH_CHECK(
-      startSeconds >= minSeconds && startSeconds < maxSeconds,
+      startSeconds >= minSeconds,
       "Start seconds is " + std::to_string(startSeconds) +
-          "; must be in range [" + std::to_string(minSeconds) + ", " +
-          std::to_string(maxSeconds) + ").");
-  TORCH_CHECK(
-      stopSeconds <= maxSeconds,
-      "Stop seconds (" + std::to_string(stopSeconds) +
-          "; must be less than or equal to " + std::to_string(maxSeconds) +
-          ").");
+          "; must be greater than or equal to " + std::to_string(minSeconds) +
+          ".");
+
+  // Note that if we can't determine the maximum seconds from the metadata, then
+  // we assume upper range is valid.
+  std::optional<double> maxSeconds = getMaxSeconds(streamMetadata);
+  if (maxSeconds.has_value()) {
+    TORCH_CHECK(
+        startSeconds < maxSeconds.value(),
+        "Start seconds is " + std::to_string(startSeconds) +
+            "; must be less than " + std::to_string(maxSeconds.value()) + ".");
+    TORCH_CHECK(
+        stopSeconds <= maxSeconds.value(),
+        "Stop seconds (" + std::to_string(stopSeconds) +
+            "; must be less than or equal to " +
+            std::to_string(maxSeconds.value()) + ").");
+  }
 
   // Note that we look at nextPts for a frame, and not its pts or duration.
   // Our abstract player displays frames starting at the pts for that frame
@@ -1456,16 +1481,13 @@ int64_t SingleStreamDecoder::getPts(int64_t frameIndex) {
 // STREAM AND METADATA APIS
 // --------------------------------------------------------------------------
 
-int64_t SingleStreamDecoder::getNumFrames(
+std::optional<int64_t> SingleStreamDecoder::getNumFrames(
     const StreamMetadata& streamMetadata) {
   switch (seekMode_) {
     case SeekMode::exact:
       return streamMetadata.numFramesFromScan.value();
     case SeekMode::approximate: {
-      TORCH_CHECK(
-          streamMetadata.numFrames.has_value(),
-          "Cannot use approximate mode since we couldn't find the number of frames from the metadata.");
-      return streamMetadata.numFrames.value();
+      return streamMetadata.numFrames;
     }
     default:
       throw std::runtime_error("Unknown SeekMode");
@@ -1484,16 +1506,13 @@ double SingleStreamDecoder::getMinSeconds(
   }
 }
 
-double SingleStreamDecoder::getMaxSeconds(
+std::optional<double> SingleStreamDecoder::getMaxSeconds(
     const StreamMetadata& streamMetadata) {
   switch (seekMode_) {
     case SeekMode::exact:
       return streamMetadata.maxPtsSecondsFromScan.value();
     case SeekMode::approximate: {
-      TORCH_CHECK(
-          streamMetadata.durationSeconds.has_value(),
-          "Cannot use approximate mode since we couldn't find the duration from the metadata.");
-      return streamMetadata.durationSeconds.value();
+      return streamMetadata.durationSeconds;
     }
     default:
       throw std::runtime_error("Unknown SeekMode");
@@ -1539,12 +1558,22 @@ void SingleStreamDecoder::validateScannedAllStreams(const std::string& msg) {
 void SingleStreamDecoder::validateFrameIndex(
     const StreamMetadata& streamMetadata,
     int64_t frameIndex) {
-  int64_t numFrames = getNumFrames(streamMetadata);
   TORCH_CHECK(
-      frameIndex >= 0 && frameIndex < numFrames,
+      frameIndex >= 0,
       "Invalid frame index=" + std::to_string(frameIndex) +
           " for streamIndex=" + std::to_string(streamMetadata.streamIndex) +
-          " numFrames=" + std::to_string(numFrames));
+          "; must be greater than or equal to 0");
+
+  // Note that if we do not have the number of frames available in our metadata,
+  // then we assume that the frameIndex is valid.
+  std::optional<int64_t> numFrames = getNumFrames(streamMetadata);
+  if (numFrames.has_value()) {
+    TORCH_CHECK(
+        frameIndex < numFrames.value(),
+        "Invalid frame index=" + std::to_string(frameIndex) +
+            " for streamIndex=" + std::to_string(streamMetadata.streamIndex) +
+            "; must be less than " + std::to_string(numFrames.value()));
+  }
 }
 
 // --------------------------------------------------------------------------

src/torchcodec/_core/SingleStreamDecoder.h

@@ -304,9 +304,9 @@ class SingleStreamDecoder {
   // index. Note that this index may be truncated for some files.
   int getBestStreamIndex(AVMediaType mediaType);
 
-  int64_t getNumFrames(const StreamMetadata& streamMetadata);
+  std::optional<int64_t> getNumFrames(const StreamMetadata& streamMetadata);
   double getMinSeconds(const StreamMetadata& streamMetadata);
-  double getMaxSeconds(const StreamMetadata& streamMetadata);
+  std::optional<double> getMaxSeconds(const StreamMetadata& streamMetadata);
 
   // --------------------------------------------------------------------------
   // VALIDATION UTILS

test/test_decoders.py

@@ -597,10 +597,10 @@ def test_get_frames_played_at(self, device, seek_mode):
     def test_get_frames_played_at_fails(self, device, seek_mode):
         decoder = VideoDecoder(NASA_VIDEO.path, device=device, seek_mode=seek_mode)
 
-        with pytest.raises(RuntimeError, match="must be in range"):
+        with pytest.raises(RuntimeError, match="must be greater than or equal to"):
             decoder.get_frames_played_at([-1])
 
-        with pytest.raises(RuntimeError, match="must be in range"):
+        with pytest.raises(RuntimeError, match="must be less than"):
             decoder.get_frames_played_at([14])
 
         with pytest.raises(RuntimeError, match="Expected a value of type"):