[H264][Simulcast] Implement the simulcast logic for h264 encoder

Simulcast logic is not implemented for h264 encoder in webrtc stack. I have implemented that based on the vp8 logic.

Please note that a set of helper functions are redundantly copied into h264EncoderImpl class just so we follow the same logic for bitrate allocation and such.

In the future a refactor is necessary to pull out the common parts into a simulcast layer above.

[maryam, 2016-05-03 20:37:32]

Description was changed from

==========
[H264][Simulcast] Implement the simulcast logic for h264 encoder

Simulcast logic is not implemented for h264 encoder in webrtc stack, have
implemented that based on the vp8 logic.
Please note that a set of helper functions are redundantly copied into
h264EncoderImpl class just so we follow the same logic for bitrate allocation
and such.
In future a refactor is necessary to pull out the common parts into a simulcast
layer above.
==========

to

==========
Simulcast logic is not implemented for h264 encoder in webrtc stack, have
implemented that based on the vp8 logic.

Please note that a set of helper functions are redundantly copied into
h264EncoderImpl class just so we follow the same logic for bitrate allocation
and such.

In future a refactor is necessary to pull out the common parts into a simulcast
layer above.
==========

[maryam, 2016-05-03 20:37:32]

maryam@highfive.com changed reviewers:
+ braveyao@webrtc.org, pbos@webrtc.org

[maryam, 2016-05-03 21:16:16]

Description was changed from

==========
Simulcast logic is not implemented for h264 encoder in webrtc stack, have
implemented that based on the vp8 logic.

Please note that a set of helper functions are redundantly copied into
h264EncoderImpl class just so we follow the same logic for bitrate allocation
and such.

In future a refactor is necessary to pull out the common parts into a simulcast
layer above.
==========

to

==========
Simulcast logic is not implemented for h264 encoder in webrtc stack. I have
implemented that based on the vp8 logic.

Please note that a set of helper functions are redundantly copied into
h264EncoderImpl class just so we follow the same logic for bitrate allocation
and such.

In the future a refactor is necessary to pull out the common parts into a
simulcast layer above.
==========

[pbos-webrtc, 2016-05-23 07:35:35]

pbos@webrtc.org changed reviewers:
+ sprang@webrtc.org

[pbos-webrtc, 2016-05-23 07:35:35]

Sorry, I've been late getting to this.

I'd like the simulcast logic to be based on SimulcastEncoderAdapter, which is
currently in VP8-only code (but the code is in general not VP8 specific). Is
this something we could break out and avoid having multiple simulcast
implementations?

webrtc/modules/video_coding/codecs/vp8/simulcast_encoder_adapter.cc is where
it's at at the moment.

+R sprang@ who has been looking into/doing refactoring in this area
(SimulcastEncoderAdapter) recently. Perhaps we could change the
VideoEncoderFactory here to take a codec type.

[pbos-webrtc, 2017-03-16 18:10:32]

pbos@webrtc.org changed reviewers:
- pbos@webrtc.org

[sprang_webrtc, 2017-03-29 08:44:21]

Whoa, this was old. Has it been forgotten in my queue all this time?
Really needs unit tests, but otherwise looks good.

https://codereview.webrtc.org/1952443002/diff/20001/webrtc/modules/video_codi...
File webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.cc (right):

https://codereview.webrtc.org/1952443002/diff/20001/webrtc/modules/video_codi...
webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.cc:434: int32_t
H264EncoderImpl::SetRates(uint32_t bitrate, uint32_t framerate) {
This is deprecated. Please use SetRateAllocation() instead, and make sure
SimulcastRateAllocator is used for H264 as well in
VideoCodecInitializer::CreateBitrateAllocator(). May have to make some
modifications related to temporal layers though.

https://codereview.webrtc.org/1952443002/diff/20001/webrtc/modules/video_codi...
File webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.h (right):

https://codereview.webrtc.org/1952443002/diff/20001/webrtc/modules/video_codi...
webrtc/modules/video_coding/codecs/h264/h264_encoder_impl.h:91:
std::vector<bool> key_frame_request_;
These vectors and encoders_ have to match index wise, right? If so, can we put
them in a struct and have a single vector instead?

[hemanth, 2017-04-20 05:55:14]

I am Hemanth from Highfive and am continuing Maryam's work here. Back on the
bug: https://bugs.chromium.org/p/webrtc/issues/detail?id=5840#c11
I posted a patch for the more generalized SimulcastEncoderAdapter that pbos
asked for above last year along with a couple of questions on some design
choices to be made.

Would you prefer we finish this patch based on the changes sprang requested, or
take that other general patch forward and abandon this?