From 8071dca3d595a4fc5f9b3ee9f667e2c3e4a35517 Mon Sep 17 00:00:00 2001
From: Moritz Bunkus <moritz@bunkus.org>
Date: Fri, 14 Sep 2012 22:26:14 +0200
Subject: [PATCH] matroska: implement support for ALAC

Support Matroska native formatting.

On demuxing reconstruct the 36-bytes QuickTime atom that the ALAC
decoder expects by prepending the "atom size", "tag" and
"tag version" fields missing from the Matroska's CodecPrivate
element.

On muxing remove the initial 12 bytes

Sample files are available:
http://www.bunkus.org/videotools/mkvtoolnix/samples/alac/alac-in-matroska.mka
and the CoreAudio file it was created from with today's mkvmerge:
http://www.bunkus.org/videotools/mkvtoolnix/samples/alac/alac-in-matroska-source.caf

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
---
 libavformat/matroska.c    |  1 +
 libavformat/matroskadec.c | 13 +++++++++++++
 libavformat/matroskaenc.c | 10 ++++++++++
 3 files changed, 24 insertions(+)

diff --git a/libavformat/matroska.c b/libavformat/matroska.c
index d2d07a8eca..652e4d0b03 100644
--- a/libavformat/matroska.c
+++ b/libavformat/matroska.c
@@ -24,6 +24,7 @@
 const CodecTags ff_mkv_codec_tags[]={
     {"A_AAC"            , AV_CODEC_ID_AAC},
     {"A_AC3"            , AV_CODEC_ID_AC3},
+    {"A_ALAC"           , AV_CODEC_ID_ALAC},
     {"A_DTS"            , AV_CODEC_ID_DTS},
     {"A_EAC3"           , AV_CODEC_ID_EAC3},
     {"A_FLAC"           , AV_CODEC_ID_FLAC},
diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index ff2a6c29dc..69a8c7f06e 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -1528,6 +1528,19 @@ static int matroska_read_header(AVFormatContext *s)
                 extradata_size = 5;
             } else
                 extradata_size = 2;
+        } else if (codec_id == AV_CODEC_ID_ALAC && track->codec_priv.size) {
+            /* Only ALAC's magic cookie is stored in Matroska's track headers.
+               Create the "atom size", "tag", and "tag version" fields the
+               decoder expects manually. */
+            extradata_size = 12 + track->codec_priv.size;
+            extradata = av_mallocz(extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
+            if (extradata == NULL)
+                return AVERROR(ENOMEM);
+            AV_WB32(extradata, extradata_size);
+            memcpy(&extradata[4], "alac", 4);
+            AV_WB32(&extradata[8], 0);
+            memcpy(&extradata[12], track->codec_priv.data,
+                                   track->codec_priv.size);
         } else if (codec_id == AV_CODEC_ID_TTA) {
             extradata_size = 30;
             extradata = av_mallocz(extradata_size);
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 9d9c223dbb..521f6b5c1a 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -475,6 +475,16 @@ static int mkv_write_codecprivate(AVFormatContext *s, AVIOContext *pb, AVCodecCo
             ret = ff_flac_write_header(dyn_cp, codec, 1);
         else if (codec->codec_id == AV_CODEC_ID_H264)
             ret = ff_isom_write_avcc(dyn_cp, codec->extradata, codec->extradata_size);
+        else if (codec->codec_id == AV_CODEC_ID_ALAC) {
+            if (codec->extradata_size < 36) {
+                av_log(s, AV_LOG_ERROR,
+                       "Invalid extradata found, ALAC expects a 36-byte "
+                       "QuickTime atom.");
+                ret = AVERROR_INVALIDDATA;
+            } else
+                avio_write(dyn_cp, codec->extradata + 12,
+                                   codec->extradata_size - 12);
+        }
         else if (codec->extradata_size)
             avio_write(dyn_cp, codec->extradata, codec->extradata_size);
     } else if (codec->codec_type == AVMEDIA_TYPE_VIDEO) {