[Libav-user] Logging in multi-stream multi-threaded video processing service

Alexander Shumsky alex3d at netup.ru
Tue Jan 10 13:23:25 EET 2017

Hi all!

We are developing multi-stream multi-threaded video processing service and
would like to improve log usefulness by including media-stream identifier.

So instead of
[mp4 @ 0x313b820] Application provided invalid, non monotonically ...
We would like to get something like
[live stream #5] [mp4 @ 0x313b820] Application provided invalid, ...

I've found similar discussion in libav-user 2012 archives but it's not 
much helpful:

Now we are considering three options:
1) Register all contexts we create in context registry singleton.
    - we should also register indirectly created contexts
      (e.g. codecs created by avformat_open_input)
    - some indirectly created contexts probably can log before we register
      it or can be created on-demand and we won't register it
2) Set thread-local media-stream identifier before calling libav functions.
    - this won't work for threads created inside context
      (e.g. multi-threaded codecs)
3) Inject stream identifier into some field in context (opaque or metadata)
    - it seems that there is no reliable way to inject data into context.
      Some contexts contain opaque or metadata field, others don't 
contain both
    - same cons as in registry option

Probably we are missing something and there are better ways to achieve 
our goal?
What is the best practices of logging in multi-stream libav video 
processing services?

С уважением, Шумский Александр
Компания NetUP

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