fix: FFmpeg end-of-stream handling breaks stream contract

src/Aurio.FFmpeg.UnitTest/FFmpegSourceStreamTests.cs

@@ -239,5 +239,30 @@ out It.Ref<Type>.IsAny
                 Times.Exactly(3)
             );
         }
+
+        [Fact]
+        public void SeekBeyondEnd_PositionCanBeSet()
+        {
+            var fileInfo = new FileInfo("./Resources/sine440-44100-16-mono-200ms.ts");
+            var s = new FFmpegSourceStream(fileInfo);
+            var position = 10000000000 * s.SampleBlockSize;
+
+            s.Position = position;
+
+            Assert.Equal(position, s.Position);
+        }
+
+        [Fact]
+        public void SeekBeyondEnd_ReadIndicatesEndOfStream()
+        {
+            var fileInfo = new FileInfo("./Resources/sine440-44100-16-mono-200ms.ts");
+            var s = new FFmpegSourceStream(fileInfo);
+            var position = 10000000000 * s.SampleBlockSize;
+
+            s.Position = position;
+            var bytesRead = s.Read(new byte[1000], 0, 1000);
+
+            Assert.Equal(0, bytesRead);
+        }
     }
 }

src/Aurio.FFmpeg/FFmpegSourceStream.cs

@@ -175,7 +175,12 @@ private void ForwardReadUntilTimestamp(long targetTimestamp)
             {
                 ReadFrame();
 
-                if (readerPosition == previousReaderPosition)
+                if (readerPosition == -1)
+                {
+                    // "Timestamp not found (end of file reached)"
+                    return;
+                }
+                else if (readerPosition == previousReaderPosition)
                 {
                     // Prevent an endless read-loop in case the reported position does not change.
                     // I did not encounter this behavior, but who knows how FFmpeg acts on the myriad of supported formats.
@@ -221,6 +226,16 @@ public long Position
                     ForwardReadUntilTimestamp(seekTarget);
                 }
 
+                if (sourceBufferLength == -1)
+                {
+                    // End of stream handling:
+                    // The Aurio stream interface allows seeking beyond the end, so we act
+                    // like the seek was successful. `Read` won't return any samples though.
+                    readerPosition = seekTarget;
+                    sourceBufferPosition = 0;
+                    return;
+                }
+
                 // check if seek ended up at seek target (or earlier because of frame size, depends on file format and stream codec)
                 if (seekTarget == readerPosition)
                 {
@@ -284,7 +299,7 @@ public int Read(byte[] buffer, int offset, int count)
                     out Type type
                 );
 
-                if (newPosition == -1 || sourceBufferLength == -1)
+                if (sourceBufferLength == -1)
                 {
                     return 0; // end of stream
                 }