From 3896cd11a107f241f06b06a336322aef2f372fdd Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michaelni@gmx.at>
Date: Mon, 15 Oct 2012 15:58:44 +0200
Subject: [PATCH] mxfenc: explicitly truncate continuity count.
The field is intended to overflow and have only its low 16bits stored.
This commit avoids the implicit truncation and clarifies that its
intended and not a bug
S326m section 7.6 ("Continuity count"):
> The continuity count word consists of 2 bytes allow-
> ing a number to be created by a modulo 65536
> counter (bits C15 to C0 in figure 7). The continuity
> count shall increment by 1 for each newly transmit-
> ted content package with the same SDTI source and
> destination addresses. The continuity count may
> be used to detect whether the content package
> sequence has been broken by an operation such as
> a routing switch.
Approved-by: Tjoppen
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
---
libavformat/mxfenc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
index b7e9449209d..6a27d2a03bd 100644
--- a/libavformat/mxfenc.c
+++ b/libavformat/mxfenc.c
@@ -1820,7 +1820,7 @@ static void mxf_write_system_item(AVFormatContext *s)
avio_w8(pb, 0x04); // content package rate
avio_w8(pb, 0x00); // content package type
avio_wb16(pb, 0x00); // channel handle
- avio_wb16(pb, mxf->tc.start + frame); // continuity count
+ avio_wb16(pb, (mxf->tc.start + frame) & 0xFFFF); // continuity count, supposed to overflow
if (mxf->essence_container_count > 1)
avio_write(pb, multiple_desc_ul, 16);
else {
--
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