From 4c886d613df8b217c6d62cb2c94e88f848177b23 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Reimar=20D=C3=B6ffinger?= <Reimar.Doeffinger@gmx.de>
Date: Tue, 22 Mar 2011 14:22:07 -0400
Subject: [PATCH] Detect byte-swapped AC-3 and support decoding it directly.
This allows the AC-3 decoder to be used directly with RealMedia
decoders that unlike the libavformat one do not byte-swap automatically.
Since the new code is only used in case we would fail directly otherwise
there should be no risk for regressions.
---
libavcodec/ac3dec.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index a9a67ced333..071cc6a54f9 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -1314,6 +1314,11 @@ static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size,
/* copy input buffer to decoder context to avoid reading past the end
of the buffer, which can be caused by a damaged input stream. */
+ if (buf_size >= 2 && AV_RB16(buf) == 0x770B) {
+ // seems to be byte-swapped AC-3
+ int cnt = FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE) >> 1;
+ s->dsp.bswap16_buf((uint16_t *)s->input_buffer, (const uint16_t *)buf, cnt);
+ } else
memcpy(s->input_buffer, buf, FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE));
buf = s->input_buffer;
/* initialize the GetBitContext with the start of valid AC-3 Frame */
--
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