matroskaenc: add an option to put the index at the start of the file

1 files changed, 21 insertions, 0 deletions

diff --git a/doc/muxers.texi b/doc/muxers.texi
index 3f84450cfa..742e72aa02 100644
--- a/doc/muxers.texi
+++ b/doc/muxers.texi
@@ -373,6 +373,27 @@ For example a 3D WebM clip can be created using the following command line:
 avconv -i sample_left_right_clip.mpg -an -c:v libvpx -metadata STEREO_MODE=left_right -y stereo_clip.webm
 @end example
 
+This muxer supports the following options:
+
+@table @option
+
+@item reserve_index_space
+By default, this muxer writes the index for seeking (called cues in Matroska
+terms) at the end of the file, because it cannot know in advance how much space
+to leave for the index at the beginning of the file. However for some use cases
+-- e.g.  streaming where seeking is possible but slow -- it is useful to put the
+index at the beginning of the file.
+
+If this option is set to a non-zero value, the muxer will reserve a given amount
+of space in the file header and then try to write the cues there when the muxing
+finishes. If the available space does not suffice, muxing will fail. A safe size
+for most use cases should be about 50kB per hour of video.
+
+Note that cues are only written if the output is seekable and this option will
+have no effect if it is not.
+
+@end table
+
 @section segment
 
 Basic stream segmenter.