commit cd4ab49ee7a543836793494b8ba3568694b612c7
author Danil Chapovalov <danilchap@webrtc.org> Thu Sep 02 11:37:54 2021
committer WebRTC LUCI CQ <webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Sep 02 13:24:31 2021
tree bb99a73bec68d866b60ba17054fdb415d9d2b779
parent d3bf4d4142457ad9ed0882dec2317b3f18c0919e

in Vp9UncompressedHeaderParser fix reading delta quantization parameter

delta_q is encoded as signed integer (s(4)) that uses extra bit for the
sign. See VP9 Bitstream Specification section 6.2.10 Delta quantizer syntax

Bug: None
Change-Id: Ib458c2a2ded3c4d6c153b6bedd29c48ef12cc538
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/231125
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#34908}

modules/video_coding/utility/vp9_uncompressed_header_parser.cc

diff --git a/modules/video_coding/utility/vp9_uncompressed_header_parser.cc b/modules/video_coding/utility/vp9_uncompressed_header_parser.cc
index d8f24be..867967d 100644
--- a/modules/video_coding/utility/vp9_uncompressed_header_parser.cc
+++ b/modules/video_coding/utility/vp9_uncompressed_header_parser.cc
@@ -145,7 +145,10 @@
   frame_info->is_lossless = frame_info->base_qp == 0;
   for (int i = 0; i < 3; ++i) {
     if (br.Read<bool>()) {  // if delta_coded
-      if (br.ReadBits(4) != 0) {
+      // delta_q is a signed integer with leading 4 bits containing absolute
+      // value and last bit containing sign. There are are two ways to represent
+      // zero with such encoding.
+      if ((br.ReadBits(5) & 0b1111'0) != 0) {  // delta_q
         frame_info->is_lossless = false;
       }
     }

modules/video_coding/utility/vp9_uncompressed_header_parser_unittest.cc

diff --git a/modules/video_coding/utility/vp9_uncompressed_header_parser_unittest.cc b/modules/video_coding/utility/vp9_uncompressed_header_parser_unittest.cc
index be0a303..d8cc738 100644
--- a/modules/video_coding/utility/vp9_uncompressed_header_parser_unittest.cc
+++ b/modules/video_coding/utility/vp9_uncompressed_header_parser_unittest.cc
@@ -72,7 +72,7 @@
 TEST(Vp9UncompressedHeaderParserTest, SegmentationWithDefaultPredProbs) {
   const uint8_t kHeader[] = {0x90, 0x49, 0x83, 0x42, 0x80, 0x2e,
                              0x30, 0x0,  0xb0, 0x0,  0x37, 0xff,
-                             0xd,  0x0,  0x0,  0x0,  0x0,  0x0};
+                             0x06, 0x80, 0x0,  0x0,  0x0,  0x0};
   absl::optional<Vp9UncompressedHeader> frame_info =
       ParseUncompressedVp9Header(kHeader);
   ASSERT_TRUE(frame_info.has_value());
@@ -82,7 +82,7 @@
 
 TEST(Vp9UncompressedHeaderParserTest, SegmentationWithSkipLevel) {
   const uint8_t kHeader[] = {0x90, 0x49, 0x83, 0x42, 0x80, 0x2e, 0x30, 0x00,
-                             0xb0, 0x00, 0x37, 0xff, 0x0d, 0x00, 0x02, 0x10,
+                             0xb0, 0x00, 0x37, 0xff, 0x06, 0x80, 0x01, 0x08,
                              0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
   absl::optional<Vp9UncompressedHeader> frame_info =
       ParseUncompressedVp9Header(kHeader);