Change-Id: Ic6a0c3a4b3bb00584d1e9dcdda0b50bdebab87aa

Added drop_frame support in multi-resolution encoder.

If one frame is dropped at a lower-resolution level, the next
upper-resolution level encoder needs to encode that frame
independently without any lower-resolution level motion
information.

Another issue is that if one frame is dropped at some but not all
resolution levels, a frame after that one may use different set
of reference frames at different resolution levels. This reference
frame asynchronization could degrade motion search precision in
upper-resolution level encoding, which uses lower-resolution level
motion result. This change compares the lower-resolution and upper-
resolution level's reference frames. If they are not the same, the
upper-resolution level encoder can not use lower-resolution level
motion result.

Change-Id: I61afa4f313630e75b7cbdd5742e230e8724a988a

Using if(); triggers an empty body warning with clang

Change-Id: I0fa2ee676400a974b40f8eaafca9ae668107eebb

In multi-resolution encoding, frame_type decision for each frame
is made by the lowest-resolution encoder. For all other higher-
resolution encoders, kf_mode is always set to VPX_KF_DISABLED,
and they are forced to use the same frame_type picked by the
lowest-resolution encoder.

Change-Id: Ic4d52ec65bbc012ca9c2d236210e28a295591eaf

Move the notion of 0 bitrate implying skip deeper into the codec,
rather than doing it at the multi-encoder API level. This preserves
v1.0.0 ABI compatibility, rather than forcing a bump to v2.0.0 over a
minor change. Also, this allows the case where the application can
selectively enable and disable the larger resolution(s) without having
to reinitialize the codec instace (for instance, if no target is
receiving the full resolution stream).

It's not clear how deep to push this check. It may be valuable to
allow the framerate adaptation code to run, for example. Currently put
the check as early as possible for simplicity, should reevaluate this
as this feature gains real use.

Change-Id: I371709b8c6b52185a1c71a166a131ecc244582f0

Move the notion of 0 bitrate implying skip deeper into the codec,
rather than doing it at the multi-encoder API level. This preserves
v1.0.0 ABI compatibility, rather than forcing a bump to v2.0.0 over a
minor change. Also, this allows the case where the application can
selectively enable and disable the larger resolution(s) without having
to reinitialize the codec instace (for instance, if no target is
receiving the full resolution stream).

It's not clear how deep to push this check. It may be valuable to
allow the framerate adaptation code to run, for example. Currently put
the check as early as possible for simplicity, should reevaluate this
as this feature gains real use.

Change-Id: I371709b8c6b52185a1c71a166a131ecc244582f0

Sometimes, a user doesn't have enough bandwidth to send high-resolution
(i.e. HD) video even though the camera catches HD video. This change
allowed users to skip highest-resolution encoding by setting that level's
target bit rate to 0.

To test it, modify the following line in vp8_multi_resolution_encoder.c.
    unsigned int  target_bitrate[NUM_ENCODERS]={1400, 500, 100};
To skip the highest-resolution level, change it to
    unsigned int  target_bitrate[NUM_ENCODERS]={0, 500, 100};
To skip the first and second highest resolution levels, change it to
    unsigned int  target_bitrate[NUM_ENCODERS]={0, 0, 100};

This change also fixed a small problem in mapping, which slightly helped
quality and performance.

Change-Id: I977bae9a9fbfba85c8be4bd5af01539f2b84bc81

Aligned the image buffer and stride to 32 bytes. This enables
calling of optimized scaler function in libyuv, and improves
the performance.

Tested libyuv scaler(x86 optimization) on Linux and Windows,
including: Linux 32/64bit, visual studio 32/64bit, Cygwin, and
MinGW32.

Also, fixed a wrong pointer in vpx_codec_encode().

Change-Id: Ibe97d7a0a745f82c43852fa4ed719be5a4db6abc

The example encoder down-samples the input video frames a number of
times with a down-sampling factor, and then encodes and outputs
bitstreams with different resolutions.

Support arbitrary down-sampling factor, and down-sampling factor
can be different for each encoding level.

For example, the encoder can be tested as follows.
1. Configure with multi-resolution encoding enabled:
../libvpx/configure --target=x86-linux-gcc --disable-codecs
--enable-vp8 --enable-runtime_cpu_detect --enable-debug
--disable-install-docs --enable-error-concealment
--enable-multi-res-encoding
2. Run make
3. Encode:
If input video is 1280x720, run:
./vp8_multi_resolution_encoder 1280 720 input.yuv 1.ivf 2.ivf 3.ivf 1
(output: 1.ivf(1280x720); 2.ivf(640x360); 3.ivf(320x180).
The last parameter is set to 1/0 to show/not show PSNR.)
4. Decode:
./simple_decoder 1.ivf 1.yuv
./simple_decoder 2.ivf 2.yuv
./simple_decoder 3.ivf 3.yuv
5. View video:
mplayer 1.yuv -demuxer rawvideo -rawvideo w=1280:h=720 -loop 0 -fps 30
mplayer 2.yuv -demuxer rawvideo -rawvideo w=640:h=360 -loop 0 -fps 30
mplayer 3.yuv -demuxer rawvideo -rawvideo w=320:h=180 -loop 0 -fps 30

The encoding parameters can be modified in vp8_multi_resolution_encoder.c,
for example, target bitrate, frame rate...

Modified API. John helped a lot with that. Thanks!

Change-Id: I03be9a51167eddf94399f92d269599fb3f3d54f5