Rewrite tags

[g-braeunlich]

Hello! Also not a bug but a question:
So far I could successfully read tags from a mkv file using a mkv_element::view::MatroskaView.
Is there also functionality to write back changed tags to the file without reqriting cluster data?

[g-braeunlich]

In the mean time, I figured it out. The current version of mkv_element does not seem to provide high level functionality to rewrite parts of a mkv file. But it provides valuable low level routines.
Some observations / suggestions:

• mkv_element::view::MatroskaView was doing a bit more than I wanted (it reads more element bodies than I needed) -> switched to lower level routines.
• What is the usecase of mkv_element::io::WriteElement? This seems to require a header already which in turn requires the size of the body which is only known after the element has been written.
• SeekPosition is implemented using Bytes. But actually, the mkv spec says that ids of top level elements and in particular ids which go into the seek head always must be encoded using 4 bytes -> SeekPosition could be implemented a bit stricter using [u8;4] instead.
• For my experiment, instead of a MatroskaView, I used a seek head. As the mkv spec allows mkv files without a seek head, I wrote a function which either loads the seek head if present, or seeks through the mkv top level elements (without reading the body) to reconstruct the seek head. This is something, I could contribute back, if desired.
• Another handy routine: replace existing elements by void elements (hinted by the mkv spec). Therefore, I wrote a function which writes a void element with given total size (header + body). Also something I could contribute.
• For the last step, I have a solution which sometimes needs to encode a VInt64 with more octets than needed (which is allowed by the ebml spec). This would also be a functionality which I would put on my wish list for a future version of mkv_element

[g-braeunlich]

@b01o nobody at home here?