picture encoding heuristics tweaks

[Antoine Martin]

Based on log samples from #2029, #2022 and others:

• maybe use x264 ahead of vpx in more cases (changes to "size-efficiency" attribute?): the bandwidth cost of vp8 / vp9 varies more (which hurts bandwidth management) and / or encode faster (currently double that of x264 at similar speed settings)
• take min-speed and min-quality into account when calculation their corollary
• ensure we don't choose YUV444P csc step
• always try to maintain 25fps, drop speed and quality to try to achieve it
• take scaling attribute into account when using the number of pixels/s
• honour fixed quality / speed: heuristics use min values only at the moment

Better unit tests.

[Antoine Martin]

Related changesets and tickets:

• r21010 + r21011 + r21012 + r21015 : calculations tweaks
• r21016: cap speed with high frame delays
• r21021 + r21027 (+r21028, r21060 fixups): speed and quality re-work
• #2044
• r21095 better debug logging

[Antoine Martin]

Updates:

• r21098: when min-speed is high, lower the quality quicker
• r21104: prefer x264 over vpx
• r21105: raise initial quality but allow fewer soft-expired regions then gradually increase the limit
• r21108: simplify speed target calculation code
• r21110: video pipeline scoring improvements
• r21112: code cleanup, makes debug output much more readable

[Antoine Martin]

See also / updates:

• ticket:1921#comment:34 and r21117 + r21118 + r21119 + r21120: make the debug and info output more compact
• r21127: avoid subsampling with shadow servers (#2029)
• r21126: avoid unnecessary calculations
• r21124: mmap fix
• #2037

[stdedos]

Replying to Antoine Martin:

• always try to maintain 25fps, drop speed and quality to try to achieve it

Minor comment: I would say, given "heuristics", I would prefer 15fps with a non-pixelated output (so that output is legible), rather than 25fps with borked quality. If there is no such heuristic in the code.

[Antoine Martin]

Minor comment: I would say, given "heuristics", I would prefer 15fps with a non-pixelated output (so that output is legible), rather than 25fps with borked quality. If there is no such heuristic in the code.

There is: just raise the min-quality.

[Antoine Martin]

Many important heuristics updates recorded in ticket:2090#comment:6 and ticket:2090#comment:7.

[Antoine Martin]

And also: ticket:2090#comment:10