[FFmpeg-devel] [PATCH 4/6] avformat/argo_asf: add version_major and version_minor options

[Zane van Iperen]

On Sat, 8 Aug 2020 12:15:01 +0200
"Andreas Rheinhardt" <andreas.rheinhardt at gmail.com> wrote:

> The version fields in the structure mimic the way the header is set up:
> They are uint16_t. Yet the fields will be written with a pointer to int
> (that's a consequence of using AV_OPT_TYPE_INT). This means that (most
> likely) an unaligned pointer will be used to write one of them (most
> likely the minor version) which is undefined behaviour. Furthermore this
> won't work on big endian systems: When you write the major version, the
> actual lower 16 bits (that matter) will be put into the minor version
> (assuming no padding between the two versions) which will afterwards be
> overwritten by the upper 16 bits of the minor version. The actual minor
> version will be written into the upper 16 bits of the number of chunks
> (again, assuming no padding). And finally, even on little-endian systems
> it only works if the minor version is specified after the major version:
> If you provide a major version via av_opt_set() (or via the ffmpeg
> command line), it will zero the minor version even on little-endian
> systems. In case no options are provided, this furthermore only works if
> av_opt_set_defaults() applies options earlier in the AVOptions first. I
> don't think such a dependency should exist.
> 
> This is of course another reason to use a separate context for the muxer.

...I remember catching this when I had separate structures. I mustn't
have updated it when I merged them. *sigh*, well done Zane.