| Message ID | 20200502171700.28991-7-andreas.rheinhardt@gmail.com |
|---|---|
| State | Accepted |
| Commit | 575557ce665238832e792e2886ee05f592e9dd11 |
| Headers | show |
| Series | [FFmpeg-devel,1/6] avformat/matroskaenc: Move adding SeekEntry into end_ebml_master_crc32() | expand |
| Context | Check | Description |
|---|---|---|
| andriy/default | pending | |
| andriy/configure | warning | Failed to apply patch |
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c index dfc1563fc1..fd590597c9 100644 --- a/libavformat/matroskaenc.c +++ b/libavformat/matroskaenc.c @@ -2542,9 +2542,13 @@ static int mkv_write_trailer(AVFormatContext *s) } after_cues: + /* Lengths greater than (1ULL << 56) - 1 can't be represented + * via an EBML number, so leave the unknown length field. */ + if (endpos - mkv->segment_offset < (1ULL << 56) - 1) { if ((ret64 = avio_seek(pb, mkv->segment_offset - 8, SEEK_SET)) < 0) return ret64; put_ebml_length(pb, endpos - mkv->segment_offset, 8); + } ret = mkv_write_seekhead(pb, mkv, 1, mkv->info.pos); if (ret < 0)
EBML numbers are variable length numbers: Only seven bits of every byte are available to encode the number, the other bits encode the length of the number itself. So an eight byte EBML number can only encode numbers in the range 0..(2^56 - 1). And when using EBML numbers to encode the length of an EBML element, the EBML number corresponding to 2^56 - 1 is actually reserved to mean that the length of the corresponding element is unknown. And therefore put_ebml_length() asserted that the length it should represent is < 2^56 - 1. Yet there was nothing that actually guaranteed this to be true for the Segment (the main/root EBML element of a Matroska file that encompasses nearly the whole file). This commit changes this by checking in advance how big the length is and only updating the number if it is representable at all; if not, the unknown length element is not touched. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com> --- libavformat/matroskaenc.c | 4 ++++ 1 file changed, 4 insertions(+)