[FFmpeg-devel] [PATCH] avformat/matroskaenc: always reserve max aac private data

[John Stebbins]

When extra data is updated using AV_PKT_DATA_NEW_EXTRADATA, the data is
written plus extra space is reserved for the max possible size extradata.
But when extradata is written during mkv_write_header, no extra space is
reserved. So the side data update overwrites whatever follows the
extradata in the track header and results in an invalid file.
---
 libavformat/matroskaenc.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 784973a951..e6917002c4 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -728,8 +728,6 @@ static int mkv_write_native_codecprivate(AVFormatContext *s, AVIOContext *pb,
     case AV_CODEC_ID_AAC:
         if (par->extradata_size)
             avio_write(dyn_cp, par->extradata, par->extradata_size);
-        else
-            put_ebml_void(pb, MAX_PCE_SIZE + 2 + 4);
         break;
     default:
         if (par->codec_id == AV_CODEC_ID_PRORES &&
@@ -749,6 +747,7 @@ static int mkv_write_codecprivate(AVFormatContext *s, AVIOContext *pb,
     AVIOContext *dyn_cp;
     uint8_t *codecpriv;
     int ret, codecpriv_size;
+    int64_t offset;
 
     ret = avio_open_dyn_buf(&dyn_cp);
     if (ret < 0)
@@ -802,9 +801,15 @@ static int mkv_write_codecprivate(AVFormatContext *s, AVIOContext *pb,
     }
 
     codecpriv_size = avio_get_dyn_buf(dyn_cp, &codecpriv);
+    offset = avio_tell(pb);
     if (codecpriv_size)
         put_ebml_binary(pb, MATROSKA_ID_CODECPRIVATE, codecpriv,
                         codecpriv_size);
+    if (par->codec_id == AV_CODEC_ID_AAC) {
+        int filler = MAX_PCE_SIZE + 2 + 4 - (avio_tell(pb) - offset);
+        if (filler)
+            put_ebml_void(pb, filler);
+    }
     ffio_free_dyn_buf(&dyn_cp);
     return ret;
 }
@@ -2182,7 +2187,7 @@ static int mkv_check_new_extra_data(AVFormatContext *s, const AVPacket *pkt)
     switch (par->codec_id) {
     case AV_CODEC_ID_AAC:
         if (side_data_size && (s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live) {
-            int filler, output_sample_rate = 0;
+            int output_sample_rate = 0;
             ret = get_aac_sample_rates(s, side_data, side_data_size, &track->sample_rate,
                                        &output_sample_rate);
             if (ret < 0)
@@ -2195,9 +2200,6 @@ static int mkv_check_new_extra_data(AVFormatContext *s, const AVPacket *pkt)
             memcpy(par->extradata, side_data, side_data_size);
             avio_seek(mkv->tracks_bc, track->codecpriv_offset, SEEK_SET);
             mkv_write_codecprivate(s, mkv->tracks_bc, par, 1, 0);
-            filler = MAX_PCE_SIZE + 2 + 4 - (avio_tell(mkv->tracks_bc) - track->codecpriv_offset);
-            if (filler)
-                put_ebml_void(mkv->tracks_bc, filler);
             avio_seek(mkv->tracks_bc, track->sample_rate_offset, SEEK_SET);
             put_ebml_float(mkv->tracks_bc, MATROSKA_ID_AUDIOSAMPLINGFREQ, track->sample_rate);
             put_ebml_float(mkv->tracks_bc, MATROSKA_ID_AUDIOOUTSAMPLINGFREQ, output_sample_rate);
-- 
2.25.4