[FFmpeg-cvslog] Detect byte-swapped AC-3 and support decoding it directly.

[Reimar Döffinger]

ffmpeg | branch: master | Reimar Döffinger <Reimar.Doeffinger at gmx.de> | Tue Mar 22 14:22:07 2011 -0400| [4c886d613df8b217c6d62cb2c94e88f848177b23] | committer: Justin Ruggles

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.

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=4c886d613df8b217c6d62cb2c94e88f848177b23
---

 libavcodec/ac3dec.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index a9a67ce..071cc6a 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 */