[FFmpeg-devel] [PATCH v4 1/3] avformat: add fields to AVProgram/AVStream for PMT change tracking

[Jan Ekström]

On Sun, May 20, 2018 at 1:54 PM, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
>
> Reading the original submission above, isn't the whole point of the
> patch to add public symbols to help downstream with real-world
> issues?
>
> Carl Eugen

Yes, currently the API user has no visibility over how the programs
are being updated. Two alternative takes on this were listed in the
commit message, one being a call-back and another being a custom data
packet from stream id 0.

So yes, the pmt_version is most definitely meant to be publicly
utilized, with it the proper utilization would go as follows:
1) API client picks the program(s) it cares about, and gets the
AVProgram(s)' pointers and notes the pmt_version when it started
reading.
2) After each AVPacket read, it checks if the pmt_version was updated.
If it was, it iterates over the streams currently registered in the
AVProgram(s) it cares about.
3) If any streams got dropped, those should be no longer cared about
by the API client. If any streams got added, they should be checked by
the API client if it is interested in them.

This is an upgrade on the previous state of affairs which would have
required the following:
1) API client picks the program(s) it cares about, and gets the
AVProgram(s)' pointers.
2) After each AVPacket read, it iterates over the streams currently
registered in the AVProgram(s) it cares about.
3) If any streams got dropped, those should be no longer cared about
by the API client. If any streams got added, they should be checked by
the API client if it is interested in them.

It is not perfect, but still an upgrade, since you can just check an
integer now, instead of doing the full iteration every time you read
an AVPacket.


Best regards,
Jan