Fixed Mpeg4VcmVideoEncoder: bitmap was not vertically flipped in the …

…code path for .NET 5 targets.

SharpAvi/Codecs/MJpegWpfVideoEncoder.cs

@@ -17,12 +17,6 @@ namespace SharpAvi.Codecs
     /// <para>
     /// The implementation relies on <see cref="JpegBitmapEncoder"/>.
     /// </para>
-    /// <para>
-    /// This encoder is not fully conformant to the Motion JPEG standard, as each encoded frame is a full JPEG picture 
-    /// with its own Huffman tables, and not those fixed Huffman tables defined by the Motion JPEG standard. 
-    /// However, (at least most) modern decoders for Motion JPEG properly handle this situation.
-    /// This also produces a little overhead on the file size.
-    /// </para>
     /// </remarks>
     public sealed class MJpegWpfVideoEncoder : IVideoEncoder
     {

SharpAvi/Codecs/Mpeg4VcmVideoEncoder.cs

@@ -338,7 +338,8 @@ public unsafe int EncodeFrame(ReadOnlySpan<byte> source, Span<byte> destination,
             Argument.ConditionIsMet(4 * width * height <= source.Length,
                 "Source end offset exceeds the source length.");
 
-            fixed (void* srcPtr = source, destPtr = destination)
+            BitmapUtils.FlipVertical(source, sourceBuffer, height, width * 4);
+            fixed (void* srcPtr = sourceBuffer, destPtr = destination)
             {
                 var srcIntPtr = new IntPtr(srcPtr);
                 var destIntPtr = new IntPtr(destPtr);