Fix growing AVC file descriptor header

[loudmax]

Update the MXF header metadata after the first frame so that the parsed AVC descriptor metadata are available from the beginning.

[loudmax]

Hi,

the AVC descriptor metadata were parsed together with the first frame. However, the MXF header has already been written at this point and only placeholders have been used. Video editors, e.g. Avid or Adobe, cannot open the file without the corresponding descriptor metadata.
This patch updates the MXF header metadata after the first frame so that growing files can be read.

I noticed that Philip has retired and that this repo will be on hold for at least six months. Thank you very much for this great piece of work! I really hope that someone will be found to continue it.

Thomas

[thomasheritage]

Many thanks for your contribution. We're unable to review and merge PRs at the moment, although it might be possible in the future if there's sufficient community interest in, and peer review of, a PR.

Please refer to #114 re the future of bmx.

[thomasheritage]

Hi, thanks for your contribution.
Per #114 this repo is now being archived. You might wish to contribute to https://github.com/ebu/bmx instead.