WebVtt Ignore Zero Duration Cues

We have an assert that ensures that the end time is greater than
the start time for any cue. However we never checked that cues
had a non-zero duration when parsing them.

We will throw away cues with a duration of zero (and print a
warning message) as they are not spec compliant.

Closes: #335
Change-Id: I404e8f3a5a8d43eff75a2554db3e38e8d340f421

packager/media/formats/webvtt/webvtt_parser.cc

@@ -19,6 +19,20 @@ namespace shaka {
 namespace media {
 namespace {
 
+std::string BlockToString(const std::string* block, size_t size) {
+  std::string out = " --- BLOCK START ---\n";
+
+  for (size_t i = 0; i < size; i++) {
+    out.append("    ");
+    out.append(block[i]);
+    out.append("\n");
+  }
+
+  out.append(" --- BLOCK END ---");
+
+  return out;
+}
+
 // Comments are just blocks that are preceded by a blank line, start with the
 // word "NOTE" (followed by a space or newline), and end at the first blank
 // line.
@@ -117,12 +131,8 @@ bool WebVttParser::Parse() {
       continue;
     }
 
-    LOG(ERROR) << "Failed to determine block classification:";
-    LOG(ERROR) << " --- BLOCK START ---";
-    for (const std::string& line : block) {
-      LOG(ERROR) << "    " << line;
-    }
-    LOG(ERROR) << " --- BLOCK END ---";
+    LOG(ERROR) << "Failed to determine block classification:\n"
+               << BlockToString(block.data(), block.size());
     return false;
   }
 
@@ -130,34 +140,65 @@ bool WebVttParser::Parse() {
 }
 
 bool WebVttParser::ParseCueWithNoId(const std::vector<std::string>& block) {
-  return ParseCue("", block.data(), block.size());
+  const Status status = ParseCue("", block.data(), block.size());
+
+  if (!status.ok()) {
+    LOG(ERROR) << "Failed to parse cue: " << status.error_message();
+  }
+
+  return status.ok();
 }
 
 bool WebVttParser::ParseCueWithId(const std::vector<std::string>& block) {
-  return ParseCue(block[0], block.data() + 1, block.size() - 1);
+  const Status status = ParseCue(block[0], block.data() + 1, block.size() - 1);
+
+  if (!status.ok()) {
+    LOG(ERROR) << "Failed to parse cue: " << status.error_message();
+  }
+
+  return status.ok();
 }
 
-bool WebVttParser::ParseCue(const std::string& id,
-                            const std::string* block,
-                            size_t block_size) {
-  std::shared_ptr<TextSample> sample(new TextSample);
-  sample->set_id(id);
-
+Status WebVttParser::ParseCue(const std::string& id,
+                              const std::string* block,
+                              size_t block_size) {
   const std::vector<std::string> time_and_style = base::SplitString(
       block[0], " ", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
 
-  uint64_t start_time;
-  uint64_t end_time;
-  if (time_and_style.size() >= 3 && time_and_style[1] == "-->" &&
+  uint64_t start_time = 0;
+  uint64_t end_time = 0;
+
+  const bool parsed_time =
+      time_and_style.size() >= 3 && time_and_style[1] == "-->" &&
       WebVttTimestampToMs(time_and_style[0], &start_time) &&
-      WebVttTimestampToMs(time_and_style[2], &end_time)) {
-    sample->SetTime(start_time, end_time);
-  } else {
-    LOG(ERROR) << "Could not parse start time, -->, and end time from "
-               << block[0];
-    return false;
+      WebVttTimestampToMs(time_and_style[2], &end_time);
+
+  if (!parsed_time) {
+    return Status(
+        error::INTERNAL_ERROR,
+        "Could not parse start time, -->, and end time from " + block[0]);
   }
 
+  // According to the WebVTT spec
+  // (https://www.w3.org/TR/webvtt1/#webvtt-cue-timings) end time must be
+  // greater than the start time of the cue. Since we are seeing content with
+  // zero-duration cues in the field, we are going to drop the cue instead of
+  // failing to package.
+  //
+  // Print a warning so that those packaging content can know that their
+  // content is not spec compliant.
+  if (start_time == end_time) {
+    LOG(WARNING) << "WebVTT input is not spec compliant."
+                    " Skipping zero-duration cue\n"
+                 << BlockToString(block, block_size);
+
+    return Status::OK;
+  }
+
+  std::shared_ptr<TextSample> sample = std::make_shared<TextSample>();
+  sample->set_id(id);
+  sample->SetTime(start_time, end_time);
+
   // The rest of time_and_style are the style tokens.
   for (size_t i = 3; i < time_and_style.size(); i++) {
     sample->AppendStyle(time_and_style[i]);
@@ -168,14 +209,7 @@ bool WebVttParser::ParseCue(const std::string& id,
     sample->AppendPayload(block[i]);
   }
 
-  const Status send_result = DispatchTextSample(0, sample);
-
-  if (send_result != Status::OK) {
-    LOG(ERROR) << "Failed to send text sample down stream:"
-               << send_result.error_message();
-  }
-
-  return send_result == Status::OK;
+  return DispatchTextSample(0, sample);
 }
 
 Status WebVttParser::DispatchTextStreamInfo() {

packager/media/formats/webvtt/webvtt_parser.h

@@ -35,9 +35,9 @@ class WebVttParser : public OriginHandler {
   bool Parse();
   bool ParseCueWithNoId(const std::vector<std::string>& block);
   bool ParseCueWithId(const std::vector<std::string>& block);
-  bool ParseCue(const std::string& id,
-                const std::string* block,
-                size_t block_size);
+  Status ParseCue(const std::string& id,
+                  const std::string* block,
+                  size_t block_size);
 
   Status DispatchTextStreamInfo();
 

packager/media/formats/webvtt/webvtt_parser_unittest.cc

@@ -147,6 +147,25 @@ TEST_F(WebVttParserTest, DISABLED_ParseStyleBlocks) {
   ASSERT_OK(parser_->Run());
 }
 
+TEST_F(WebVttParserTest, IngoresZeroDurationCues) {
+  const char* text =
+      "WEBVTT\n"
+      "\n"
+      "00:01:00.000 --> 00:01:00.000\n"
+      "This subtitle would never show\n";
+
+  ASSERT_NO_FATAL_FAILURE(SetUpAndInitializeGraph(text));
+
+  {
+    testing::InSequence s;
+    EXPECT_CALL(*Output(kOutputIndex),
+                OnProcess(IsStreamInfo(kStreamIndex, kTimeScale, !kEncrypted)));
+    EXPECT_CALL(*Output(kOutputIndex), OnFlush(kStreamIndex));
+  }
+
+  ASSERT_OK(parser_->Run());
+}
+
 TEST_F(WebVttParserTest, ParseOneCue) {
   const char* text =
       "WEBVTT\n"