Commit 178b11af for libheif

commit 178b11afc84a43da8b57e17b40ce77dedb5bb414
Author: Dirk Farin <dirk.farin@gmail.com>
Date:   Thu Oct 8 15:28:44 2026 +0200

    heif-enc: fix the WebVMT parser

    The pending packet state was static and the start time an optional that
    was dereferenced before it was ever set. Use plain locals starting at 0,
    so a first cue after time 0 is preceded by an empty packet. Cues that go
    backwards in time are skipped instead of rewinding the clock.

    The sync-command regexes used '.', which does not match line breaks, so
    a sync command split over two lines (the layout in the wiki examples)
    produced an empty packet. Match any character instead.

diff --git a/examples/vmt.cc b/examples/vmt.cc
index c0e715e4..7e7fe5ca 100644
--- a/examples/vmt.cc
+++ b/examples/vmt.cc
@@ -121,14 +121,15 @@ static std::vector<uint8_t> parse_vmt_sync_data(const std::string& content)
 {
   std::vector<uint8_t> data;

-  std::regex pattern_sync(R"(\s*\{\s*\"sync\"\s*:\s*\{(.*?)\}\s*\}\s*)");
+  // [\s\S] instead of '.' because '.' does not match line breaks and a sync command may span several lines.
+  std::regex pattern_sync(R"(\s*\{\s*\"sync\"\s*:\s*\{([\s\S]*?)\}\s*\}\s*)");
   const std::sregex_token_iterator ti_end;

   for (std::sregex_token_iterator ti(content.begin(), content.end(), pattern_sync, 1); ti != ti_end; ++ti)
   {
     std::string sync = *ti;
-    std::regex pattern_type(R"(.*\"type\"\s*:\s*\"(.*?)\".*)");
-    std::regex pattern_data(R"(.*\"data\"\s*:\s*\"(.*?)\".*)");
+    std::regex pattern_type(R"([\s\S]*\"type\"\s*:\s*\"(.*?)\"[\s\S]*)");
+    std::regex pattern_data(R"([\s\S]*\"data\"\s*:\s*\"(.*?)\"[\s\S]*)");
     std::smatch match;

     if (std::regex_match(sync, match, pattern_type)) {
@@ -217,8 +218,10 @@ int encode_vmt_metadata_track(heif_context* context, heif_track* visual_track,
   std::regex pattern_cue(R"(^\s*(-?(\d|:|\.)*)\s*-->\s*(-?(\d|:|\.)*)?.*)");
   std::regex pattern_note(R"(^\s*(NOTE).*)");

-  static std::vector<uint8_t> prev_metadata;
-  static std::optional<uint32_t> prev_ts;
+  // Each cue closes the packet that was opened by the previous cue. A packet is written as soon as its duration is known.
+  // The track starts at time 0. If the first cue starts later, an empty packet covers the time before it.
+  std::vector<uint8_t> prev_metadata;
+  uint32_t prev_ts = 0;

   std::string line;
   while (std::getline(istr, line))
@@ -272,25 +275,27 @@ int encode_vmt_metadata_track(heif_context* context, heif_track* visual_track,
       concat = parse_vmt_sync_data(content);
     }

-    if (ts != BAD_VMT_TIMESTAMP) {
+    if (ts == BAD_VMT_TIMESTAMP) {
+      std::cerr << "Bad WebVMT timestamp: " << cue_start << "\n";
+      continue;
+    }

-      if (ts > *prev_ts) {
-        heif_raw_sequence_sample_set_data(sample, (const uint8_t*)prev_metadata.data(), prev_metadata.size());
-        heif_raw_sequence_sample_set_duration(sample, ts - *prev_ts);
-        heif_track_add_raw_sequence_sample(track, sample);
-      }
-      else if (ts == *prev_ts) {
-        concat.insert(concat.begin(), prev_metadata.begin(), prev_metadata.end());
-      }
-      else {
-        std::cerr << "Bad WebVMT timestamp order: " << cue_start << "\n";
-      }
+    if (ts < prev_ts) {
+      std::cerr << "Bad WebVMT timestamp order: " << cue_start << "\n";
+      continue;
+    }

-      prev_ts = ts;
-      prev_metadata = concat;
+    if (ts == prev_ts) {
+      // Cues with the same start time are combined into one packet.
+      prev_metadata.insert(prev_metadata.end(), concat.begin(), concat.end());
     }
     else {
-      std::cerr << "Bad WebVMT timestamp: " << cue_start << "\n";
+      heif_raw_sequence_sample_set_data(sample, (const uint8_t*)prev_metadata.data(), prev_metadata.size());
+      heif_raw_sequence_sample_set_duration(sample, ts - prev_ts);
+      heif_track_add_raw_sequence_sample(track, sample);
+
+      prev_ts = ts;
+      prev_metadata = concat;
     }
   }