From d4f8b330d61cb2457fa1c085510a5f0553b98d97 Mon Sep 17 00:00:00 2001
From: Torbjörn Andersson
Date: Tue, 29 May 2018 19:56:55 +0200
Subject: IMAGE: Honor nb_fields when calculating frame duration

From what I understand, this has something to do with the image
being either made up from two or three parts. When it's made from
three parts, the frame should be displayed for half again as long
as normal.

This makes the speed of the Zork: Grand Inquisitor video look
about right to me. It's still out of sync, but it doesn't seem to
get *more* out of sync as the video progresses.
---
 image/codecs/mpeg.cpp | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'image/codecs')

diff --git a/image/codecs/mpeg.cpp b/image/codecs/mpeg.cpp
index beb042dbf1..bb40fe615d 100644
--- a/image/codecs/mpeg.cpp
+++ b/image/codecs/mpeg.cpp
@@ -78,8 +78,13 @@ bool MPEGDecoder::decodePacket(Common::SeekableReadStream &packet, uint32 &frame
 			if (_mpegInfo->display_fbuf) {
 				foundFrame = true;
 				const mpeg2_sequence_t *sequence = _mpegInfo->sequence;
+				const mpeg2_picture_t *picture = _mpegInfo->display_picture;
 
 				framePeriod += sequence->frame_period;
+				if (picture->nb_fields > 2) {
+					framePeriod += (sequence->frame_period / 2);
+
+				}
 
 				if (!dst) {
 					// If no destination is specified, use our internal storage
-- 
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