Hello Nicolas,
On 05/19/2016 12:44 PM, Nicolas George wrote:
Le tridi 23 floréal, an CCXXIV, Jan Sebechlebsky a écrit :
My current idea is to create queue for each output (as Marton suggested) and
process each output in separate thread. I was also considering using just
single queue, but since the AVPackets are referenced counted, the memory
overhead is negligible and using multiple queues will simplify the code.
Apart from getting advantage of non-blocking processing with multiple slave
muxers, error handling will also be improved.
<snip>
Another question is what to do when some of the queues becomes full,
discussed options were so far:
- Block write_packet call until the queue frees - this might be useful
when producer is faster than consumer, and we don't want to drop any packets
when recording to file.
- Drop some yet unprocessed packets (until next keyframe, or free some
portion of queue) to free the queue - this might be useful for network
outputs.
I must say, I am not very happy with the direction this project takes.
Non-blocking muxers (and demuxers, and protocols) is a white whale for our
API: we really really want it, but it huge and very hard to catch.
Does this objection apply to the non-blocking full queue handling stated
above or the whole project (using threads in tee)?
It is something that needs to be implemented globally with a very careful
design. Definitely not something that can be added in a corner of an obscure
muxer. We already went down that path twice, with the thread for the UDP
protocol and with running demuxer in threads in FFmpeg. Both did lead to
endless complications: bugs, inconsistencies, portability trouble.
If you want to work on that (in order to bring these enhancements to the tee
muxer, fitting the topic of the GSoC project), you probably can. But I
expect this to be very hard. It has been rejected as a proposal for a GSoC
project in the past on the basis that it is probably too hard for a random
student. Also, I am not sure that Marton, your official mentor, would want
such a huge shift in the project's goals.
I must accept that for now I may lack the complete overview over
the project to see the potential problems which this could introduce.
However in the proposed project there is enough time to do proper
testing and eliminate the found issues and the solution described in
proposal could still be a benefit (if the ideal solution is too hard).
Also I thing the proposed changes will not bring too much complexity to
the project regarding thread handling.
I don't mind changing the plans and implementing it in other way if
it is better and achievable - but you might be right this may be too hard.
Anyway if you give me some directions, (what are the requirements for
the more general solution, what are the particular problems in the
proposed one) I can at least try to dive more into it (getting more
familiar with the project will be only a benefit).
I don't know how such changes are handled in GSoC (since I probably
wouldn't be able meet milestone if the solution would require the
complex global changes first).
Regards,
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Thanks,
Regards,
Jan S.
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