From b17e5363d6b7938f6b86a376817cf2830bc276e5 Mon Sep 17 00:00:00 2001
From: Molly Xu <mollyxu@meta.com>
Date: Mon, 17 Nov 2025 10:36:24 -0800
Subject: [PATCH] Ensure SingleStreamDecoder is robust against numFrames = 0

Summary: Ensure SingleStreamDecoder is robust against numFrames = 0

Reviewed By: NicolasHug

Differential Revision: D87109526
---
 src/torchcodec/_core/SingleStreamDecoder.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/torchcodec/_core/SingleStreamDecoder.cpp b/src/torchcodec/_core/SingleStreamDecoder.cpp
index 32d6f9d99..0b30f1fff 100644
--- a/src/torchcodec/_core/SingleStreamDecoder.cpp
+++ b/src/torchcodec/_core/SingleStreamDecoder.cpp
@@ -288,6 +288,14 @@ void SingleStreamDecoder::scanFileAndUpdateMetadataAndIndex() {
     streamMetadata.numFramesFromContent =
         streamInfos_[streamIndex].allFrames.size();
 
+    // This ensures that we are robust in handling cases where
+    // we are decoding in exact mode and numFrames is 0. The current metadata
+    // validation logic assumes that these values should not be None
+    if (streamMetadata.numFramesFromContent.value() == 0) {
+      streamMetadata.beginStreamPtsFromContent = 0;
+      streamMetadata.endStreamPtsFromContent = 0;
+    }
+
     if (streamMetadata.beginStreamPtsFromContent.has_value()) {
       streamMetadata.beginStreamPtsSecondsFromContent = ptsToSeconds(
           *streamMetadata.beginStreamPtsFromContent, avStream->time_base);