HLS: Implement the EXT-X-PLAYLIST-TYPE tag

This CL implements the EXT-X-PLAYLIST-TYPE tag, which allows the server to indicate constraints about how the playlist may change across reloads. There are only two valid types `EVENT` and `VOD`. The absence of this tag indicates that the playlist is considered "live", and may change in ways that are invalid for either `EVENT` or `VOD`. This CL adds unit tests for parsing the tag, as well as media playlists containing it. Bug: 1266991 Change-Id: Ib47a197cfffad63cf224e9d9285f532b98fa5e37 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3569572 Reviewed-by: Matthew Wolenetz <wolenetz@chromium.org> Commit-Queue: Will Cassella <cassew@chromium.org> Cr-Commit-Position: refs/heads/main@{#989232}
chromium · Apr 6, 2022 · 0429788 · 0429788
1 parent 4c0ea5f
commit 0429788
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Showing 10 changed files with 149 additions and 5 deletions.
diff --git a/media/formats/hls/items.cc b/media/formats/hls/items.cc
@@ -42,6 +42,7 @@ absl::optional<TagItem> GetTagItem(SourceString line) {
       TagNameEntry("-X-I-FRAMES-ONLY", MediaPlaylistTagName::kXIFramesOnly),
       TagNameEntry("-X-INDEPENDENT-SEGMENTS",
                    CommonTagName::kXIndependentSegments),
+      TagNameEntry("-X-PLAYLIST-TYPE:", MediaPlaylistTagName::kXPlaylistType),
       TagNameEntry("-X-VERSION:", CommonTagName::kXVersion),
       TagNameEntry("INF:", MediaPlaylistTagName::kInf),
       TagNameEntry("M3U", CommonTagName::kM3u),

diff --git a/media/formats/hls/media_playlist.cc b/media/formats/hls/media_playlist.cc
@@ -39,6 +39,7 @@ ParseStatus::Or<MediaPlaylist> MediaPlaylist::Parse(base::StringPiece source,
   absl::optional<InfTag> inf_tag;
   absl::optional<XGapTag> gap_tag;
   absl::optional<XDiscontinuityTag> discontinuity_tag;
+  absl::optional<XPlaylistTypeTag> playlist_type_tag;
   std::vector<MediaSegment> segments;
 
   // Get segments out of the playlist
@@ -105,6 +106,13 @@ ParseStatus::Or<MediaPlaylist> MediaPlaylist::Parse(base::StringPiece source,
         case MediaPlaylistTagName::kXIFramesOnly:
           // TODO(crbug.com/1266991): Implement the #EXT-X-I-FRAMES-ONLY tag
           break;
+        case MediaPlaylistTagName::kXPlaylistType: {
+          auto error = ParseUniqueTag(*tag, playlist_type_tag);
+          if (error.has_value()) {
+            return std::move(error).value();
+          }
+          break;
+        }
       }
 
       continue;
@@ -136,17 +144,24 @@ ParseStatus::Or<MediaPlaylist> MediaPlaylist::Parse(base::StringPiece source,
     discontinuity_tag.reset();
   }
 
+  absl::optional<PlaylistType> playlist_type;
+  if (playlist_type_tag) {
+    playlist_type = playlist_type_tag->type;
+  }
+
   return MediaPlaylist(std::move(uri), common_state.GetVersion(),
                        common_state.independent_segments_tag.has_value(),
-                       std::move(segments));
+                       std::move(segments), playlist_type);
 }
 
 MediaPlaylist::MediaPlaylist(GURL uri,
                              types::DecimalInteger version,
                              bool independent_segments,
-                             std::vector<MediaSegment> segments)
+                             std::vector<MediaSegment> segments,
+                             absl::optional<PlaylistType> playlist_type)
     : Playlist(std::move(uri), version, independent_segments),
-      segments_(std::move(segments)) {
+      segments_(std::move(segments)),
+      playlist_type_(playlist_type) {
   base::TimeDelta duration;
   for (const auto& segment : segments_) {
     duration += base::Seconds(segment.GetDuration());

diff --git a/media/formats/hls/media_playlist.h b/media/formats/hls/media_playlist.h
@@ -9,6 +9,8 @@
 #include "base/time/time.h"
 #include "media/base/media_export.h"
 #include "media/formats/hls/playlist.h"
+#include "media/formats/hls/tags.h"
+#include "media/formats/hls/types.h"
 
 namespace media::hls {
 
@@ -31,6 +33,16 @@ class MEDIA_EXPORT MediaPlaylist final : public Playlist {
   // actual duration.
   base::TimeDelta GetComputedDuration() const { return computed_duration_; }
 
+  // Returns the type of this playlist (as specified by the
+  // 'EXT-X-PLAYLIST-TYPE' tag). If this is present, then the server must follow
+  // the constraints detailed on `PlaylistType` when the playlist is reloaded.
+  // If this property is absent, that implies that the server may append new
+  // segments to the end or remove old segments from the beginning of this
+  // playlist upon reloading.
+  absl::optional<PlaylistType> GetPlaylistType() const {
+    return playlist_type_;
+  }
+
   // Attempts to parse the playlist represented by `source`. `uri` must be a
   // valid, non-empty GURL referring to the URI of this playlist. If the
   // playlist is invalid, returns an error. Otherwise, returns the parsed
@@ -42,10 +54,12 @@ class MEDIA_EXPORT MediaPlaylist final : public Playlist {
   MediaPlaylist(GURL uri,
                 types::DecimalInteger version,
                 bool independent_segments,
-                std::vector<MediaSegment> segments);
+                std::vector<MediaSegment> segments,
+                absl::optional<PlaylistType> playlist_type);
 
   std::vector<MediaSegment> segments_;
   base::TimeDelta computed_duration_;
+  absl::optional<PlaylistType> playlist_type_;
 };
 
 }  // namespace media::hls

diff --git a/media/formats/hls/media_playlist_unittest.cc b/media/formats/hls/media_playlist_unittest.cc
@@ -112,6 +112,12 @@ void HasVersion(types::DecimalInteger version,
   EXPECT_EQ(playlist.GetVersion(), version) << from.ToString();
 }
 
+void HasType(absl::optional<PlaylistType> type,
+             const base::Location& from,
+             const MediaPlaylist& playlist) {
+  EXPECT_EQ(playlist.GetPlaylistType(), type) << from.ToString();
+}
+
 void HasDuration(types::DecimalFloatingPoint duration,
                  const base::Location& from,
                  const MediaSegment& segment) {
@@ -388,4 +394,56 @@ TEST(HlsFormatParserTest, ParseMediaPlaylist_Define) {
   builder.ExpectOk();
 }
 
+TEST(HlsFormatParserTest, ParseMediaPlaylist_PlaylistType) {
+  TestBuilder builder;
+  builder.AppendLine("#EXTM3U");
+
+  // Without the EXT-X-PLAYLIST-TYPE tag, the playlist has no type.
+  {
+    auto fork = builder;
+    fork.ExpectPlaylist(HasType, absl::nullopt);
+    fork.ExpectOk();
+  }
+
+  {
+    auto fork = builder;
+    fork.AppendLine("#EXT-X-PLAYLIST-TYPE:VOD");
+    fork.ExpectPlaylist(HasType, PlaylistType::kVOD);
+    fork.ExpectOk();
+  }
+
+  {
+    auto fork = builder;
+    fork.AppendLine("#EXT-X-PLAYLIST-TYPE:EVENT");
+    fork.ExpectPlaylist(HasType, PlaylistType::kEvent);
+    fork.ExpectOk();
+  }
+
+  // This tag may not be specified twice
+  {
+    auto fork = builder;
+    fork.AppendLine("#EXT-X-PLAYLIST-TYPE:VOD");
+    fork.AppendLine("#EXT-X-PLAYLIST-TYPE:EVENT");
+    fork.ExpectError(ParseStatusCode::kPlaylistHasDuplicateTags);
+  }
+  {
+    auto fork = builder;
+    fork.AppendLine("#EXT-X-PLAYLIST-TYPE:VOD");
+    fork.AppendLine("#EXT-X-PLAYLIST-TYPE:VOD");
+    fork.ExpectError(ParseStatusCode::kPlaylistHasDuplicateTags);
+  }
+
+  // Unknown or invalid playlist types should trigger an error
+  {
+    auto fork = builder;
+    fork.AppendLine("#EXT-X-PLAYLIST-TYPE:FOOBAR");
+    fork.ExpectError(ParseStatusCode::kUnknownPlaylistType);
+  }
+  {
+    auto fork = builder;
+    fork.AppendLine("#EXT-X-PLAYLIST-TYPE:");
+    fork.ExpectError(ParseStatusCode::kMalformedTag);
+  }
+}
+
 }  // namespace media::hls
diff --git a/media/formats/hls/parse_status.cc b/media/formats/hls/parse_status.cc
@@ -23,6 +23,7 @@ base::StringPiece ParseStatusCodeToString(ParseStatusCode code) {
     PARSE_STATUS_CODE_CASE(kFailedToParseSignedDecimalFloatingPoint);
     PARSE_STATUS_CODE_CASE(kFailedToParseQuotedString);
     PARSE_STATUS_CODE_CASE(kInvalidPlaylistVersion);
+    PARSE_STATUS_CODE_CASE(kUnknownPlaylistType);
     PARSE_STATUS_CODE_CASE(kMalformedAttributeList);
     PARSE_STATUS_CODE_CASE(kAttributeListHasDuplicateNames);
     PARSE_STATUS_CODE_CASE(kMalformedVariableName);

diff --git a/media/formats/hls/parse_status.h b/media/formats/hls/parse_status.h
@@ -20,6 +20,7 @@ enum class ParseStatusCode : StatusCodeType {
   kFailedToParseSignedDecimalFloatingPoint,
   kFailedToParseQuotedString,
   kInvalidPlaylistVersion,
+  kUnknownPlaylistType,
   kMalformedAttributeList,
   kAttributeListHasDuplicateNames,
   kMalformedVariableName,

diff --git a/media/formats/hls/tag_name.h b/media/formats/hls/tag_name.h
@@ -54,7 +54,8 @@ enum class MediaPlaylistTagName : TagName {
   kXIFramesOnly,
   kXDiscontinuity,
   kXGap,
-  kMaxValue = kXGap,
+  kXPlaylistType,
+  kMaxValue = kXPlaylistType,
 };
 
 constexpr TagKind GetTagKind(CommonTagName) {

diff --git a/media/formats/hls/tags.cc b/media/formats/hls/tags.cc
@@ -254,4 +254,22 @@ ParseStatus::Or<XDefineTag> XDefineTag::Parse(TagItem tag) {
   return ParseStatusCode::kMalformedTag;
 }
 
+ParseStatus::Or<XPlaylistTypeTag> XPlaylistTypeTag::Parse(TagItem tag) {
+  DCHECK(tag.name == ToTagName(XPlaylistTypeTag::kName));
+
+  // This tag requires content
+  if (tag.content.Empty()) {
+    return ParseStatusCode::kMalformedTag;
+  }
+
+  if (tag.content.Str() == "EVENT") {
+    return XPlaylistTypeTag{.type = PlaylistType::kEvent};
+  }
+  if (tag.content.Str() == "VOD") {
+    return XPlaylistTypeTag{.type = PlaylistType::kVOD};
+  }
+
+  return ParseStatusCode::kUnknownPlaylistType;
+}
+
 }  // namespace media::hls
diff --git a/media/formats/hls/tags.h b/media/formats/hls/tags.h
@@ -91,6 +91,24 @@ struct XGapTag {
   static MEDIA_EXPORT ParseStatus::Or<XGapTag> Parse(TagItem);
 };
 
+enum class PlaylistType {
+  // Indicates that this playlist may have segments appended upon reloading
+  // (until the #EXT-X-ENDLIST tag appears), but segments will not be removed.
+  kEvent,
+
+  // Indicates that this playlist is static, and will not have segments appended
+  // or removed.
+  kVOD,
+};
+
+// Represents the contents of the #EXT-X-PLAYLIST-TYPE tag
+struct XPlaylistTypeTag {
+  static constexpr auto kName = MediaPlaylistTagName::kXPlaylistType;
+  static MEDIA_EXPORT ParseStatus::Or<XPlaylistTypeTag> Parse(TagItem);
+
+  PlaylistType type;
+};
+
 }  // namespace media::hls
 
 #endif  // MEDIA_FORMATS_HLS_TAGS_H_
diff --git a/media/formats/hls/tags_unittest.cc b/media/formats/hls/tags_unittest.cc
@@ -226,4 +226,21 @@ TEST(HlsFormatParserTest, ParseXDefineTagTest) {
                         ParseStatusCode::kMalformedTag);
 }
 
+TEST(HlsFormatParserTest, ParseXPlaylistTypeTagTest) {
+  RunTagIdenficationTest<XPlaylistTypeTag>("#EXT-X-PLAYLIST-TYPE:VOD\n", "VOD");
+  RunTagIdenficationTest<XPlaylistTypeTag>("#EXT-X-PLAYLIST-TYPE:EVENT\n",
+                                           "EVENT");
+
+  auto tag = OkTest<XPlaylistTypeTag>("EVENT");
+  EXPECT_EQ(tag.type, PlaylistType::kEvent);
+  tag = OkTest<XPlaylistTypeTag>("VOD");
+  EXPECT_EQ(tag.type, PlaylistType::kVOD);
+
+  ErrorTest<XPlaylistTypeTag>("FOOBAR", ParseStatusCode::kUnknownPlaylistType);
+  ErrorTest<XPlaylistTypeTag>("EEVENT", ParseStatusCode::kUnknownPlaylistType);
+  ErrorTest<XPlaylistTypeTag>(" EVENT", ParseStatusCode::kUnknownPlaylistType);
+  ErrorTest<XPlaylistTypeTag>("EVENT ", ParseStatusCode::kUnknownPlaylistType);
+  ErrorTest<XPlaylistTypeTag>("", ParseStatusCode::kMalformedTag);
+}
+
 }  // namespace media::hls