Fix packet synchronization bug

Kitware · Nov 9, 2023 · ceec1dc · ceec1dc
1 parent 900567e
commit ceec1dc
Show file tree

Hide file tree

Showing 3 changed files with 13 additions and 15 deletions.
diff --git a/arrows/ffmpeg/ffmpeg_video_output.cxx b/arrows/ffmpeg/ffmpeg_video_output.cxx
@@ -511,8 +511,6 @@ ::open_video_state(
   }
   output_format = format_context->oformat;
 
-  // Set timestamp value to start at
-  format_context->output_ts_offset = settings.start_timestamp;
   format_context->flags |= AVFMT_FLAG_AUTO_BSF;
   format_context->flags |= AVFMT_FLAG_GENPTS;
 
@@ -965,15 +963,6 @@ ::add_uninterpreted_data( vital::video_uninterpreted_data const& misc_data )
       av_packet_rescale_ts(
         tmp_packet.get(), stream.settings.time_base, stream.stream->time_base );
 
-      // Adjust for any global timestamp offset
-      auto const counter_offset =
-        av_rescale_q(
-          format_context->output_ts_offset,
-          AVRational{ 1, AV_TIME_BASE },
-          stream.stream->time_base );
-      tmp_packet->dts -= counter_offset;
-      tmp_packet->pts -= counter_offset;
-
       // Write the packet
       throw_error_code(
         av_interleaved_write_frame( format_context.get(), tmp_packet.get() ),
@@ -1002,6 +991,15 @@ ::write_next_packet()
   }
   throw_error_code( err, "Could not get next packet from encoder" );
 
+  // Adjust for any global timestamp offset
+  auto const offset =
+    av_rescale_q(
+      video_settings.start_timestamp,
+      AVRational{ 1, AV_TIME_BASE },
+      video_stream->time_base );
+  packet->dts += offset;
+  packet->pts += offset;
+
   // Succeeded; write to file
   throw_error_code(
     av_interleaved_write_frame( format_context.get(), packet.get() ),

diff --git a/arrows/ffmpeg/ffmpeg_video_settings.h b/arrows/ffmpeg/ffmpeg_video_settings.h
@@ -71,9 +71,9 @@ struct KWIVER_ALGO_FFMPEG_EXPORT ffmpeg_video_settings
   /// guaranteed to determine the time base in the output video.
   AVRational time_base;
 
-  /// Desired PTS of the first video frame, in AV_TIME_BASE units
-  /// (microseconds). For some formats, the actual first PTS may exceed this
-  /// value to ensure non-negative PTS or DTS.
+  /// Start time of the input video, in AV_TIME_BASE units (microseconds).
+  /// This information is necessary for copied and newly-encoded packets to sync
+  /// correctly.
   int64_t start_timestamp;
 
   /// FFmpeg-defined string options passed to the video codec.

diff --git a/arrows/ffmpeg/tests/test_video_output_ffmpeg.cxx b/arrows/ffmpeg/tests/test_video_output_ffmpeg.cxx
@@ -364,7 +364,7 @@ TEST_F ( ffmpeg_video_output, round_trip_audio )
 // Similar to round_trip_direct, but for a test video with an audio stream.
 TEST_F ( ffmpeg_video_output, round_trip_audio_direct )
 {
-  auto const src_path = data_dir + "/" + short_video_name;
+  auto const src_path = data_dir + "/" + audio_video_name;
   auto const tmp_path =
     kwiver::testing::temp_file_name( "test-ffmpeg-output-", ".ts" );