OpenH264
========
OpenH264 is a codec library which supports H.264 encoding and decoding. It is suitable for use in real time applications such as WebRTC. See http://www.openh264.org/ for more details.

Encoder Features
----------------
- Constrained Baseline Profile up to Level 5.2 (Max frame size is 36864 macro-blocks)
- Arbitrary resolution, not constrained to multiples of 16x16
- Rate control with adaptive quantization, or constant quantization
- Slice options: 1 slice per frame, N slices per frame, N macroblocks per slice, or N bytes per slice
- Multiple threads automatically used for multiple slices
- Temporal scalability up to 4 layers in a dyadic hierarchy
- Simulcast AVC up to 4 resolutions from a single input
- Spatial simulcast up to 4 resolutions from a single input
- Long Term Reference (LTR) frames
- Memory Management Control Operation (MMCO)
- Reference picture list modification
- Single reference frame for inter prediction
- Multiple reference frames when using LTR and/or 3-4 temporal layers
- Periodic and on-demand Instantaneous Decoder Refresh (IDR) frame insertion
- Dynamic changes to bit rate, frame rate, and resolution
- Annex B byte stream output
- YUV 4:2:0 planar input

Decoder Features
----------------
- Constrained Baseline Profile up to Level 5.2 (Max frame size is 36864 macro-blocks)
- Arbitrary resolution, not constrained to multiples of 16x16
- Single thread for all slices
- Long Term Reference (LTR) frames
- Memory Management Control Operation (MMCO)
- Reference picture list modification
- Multiple reference frames when specified in Sequence Parameter Set (SPS)
- Annex B byte stream input
- YUV 4:2:0 planar output

OS Support
----------
- Windows 64-bit and 32-bit
- Mac OS X 64-bit and 32-bit
- Mac OS X ARM64
- Linux 64-bit and 32-bit
- Android 64-bit and 32-bit
- iOS 64-bit and 32-bit
- Windows Phone 32-bit

Architectures verified to be working
----------
- ppc64el

Processor Support
-----------------
- Intel x86 optionally with MMX/SSE (no AVX yet, help is welcome)
- ARMv7 optionally with NEON, AArch64 optionally with NEON
- Any architecture using C/C++ fallback functions

Building the Library
--------------------
NASM needed to be installed for assembly code: workable version 2.10.06 or above, NASM can be downloaded from http://www.nasm.us/.
For Mac OSX 64-bit NASM needed to be below version 2.11.08 as NASM 2.11.08 will introduce error when using RIP-relative addresses in Mac OSX 64-bit

To build the arm assembly for Windows Phone, gas-preprocessor is required. It can be downloaded from git://git.libav.org/gas-preprocessor.git

For Android Builds
------------------
To build for android platform, You need to install android sdk and ndk. You also need to export `**ANDROID_SDK**/tools` to PATH. On Linux, this can be done by

    export PATH=**ANDROID_SDK**/tools:$PATH

The codec and demo can be built by

    make OS=android NDKROOT=**ANDROID_NDK** TARGET=**ANDROID_TARGET**

Valid `**ANDROID_TARGET**` can be found in `**ANDROID_SDK**/platforms`, such as `android-12`.
You can also set `ARCH`, `NDKLEVEL` according to your device and NDK version.
`ARCH` specifies the architecture of android device. Currently `arm`, `arm64`, `x86` and `x86_64` are supported, the default is `arm`. (`mips` and `mips64` can also be used, but there's no specific optimization for those architectures.)
`NDKLEVEL` specifies android api level, the default is 12. Available possibilities can be found in `**ANDROID_NDK**/platforms`, such as `android-21` (strip away the `android-` prefix).

By default these commands build for the `armeabi-v7a` ABI. To build for the other android
ABIs, add `ARCH=arm64`, `ARCH=x86`, `ARCH=x86_64`, `ARCH=mips` or `ARCH=mips64`.
To build for the older `armeabi` ABI (which has armv5te as baseline), add `APP_ABI=armeabi` (`ARCH=arm` is implicit).
To build for 64-bit ABI, such as `arm64`, explicitly set `NDKLEVEL` to 21 or higher.

For iOS Builds
--------------
You can build the libraries and demo applications using xcode project files
located in `codec/build/iOS/dec` and `codec/build/iOS/enc`.

You can also build the libraries (but not the demo applications) using the
make based build system from the command line. Build with

    make OS=ios ARCH=**ARCH**

Valid values for `**ARCH**` are the normal iOS architecture names such as
`armv7`, `armv7s`, `arm64`, and `i386` and `x86_64` for the simulator.
Another settable iOS specific parameter
is `SDK_MIN`, specifying the minimum deployment target for the built library.
For other details on building using make on the command line, see
'For All Platforms' below.

For Linux Builds
--------------

You can build the libraries (but not the demo applications) using the
make based build system from the command line. Build with

    make OS=linux ARCH=**ARCH**

 You can set `ARCH` according to your linux device .
`ARCH` specifies the architecture of the device. Currently `arm`, `arm64`, `x86` and `x86_64` are supported   

 NOTICE:
 	If your computer is x86 architecture, for build the libnary which be used on arm/aarch64 machine, you may need to use cross-compiler, for example:
 		make OS=linux CC=aarch64-linux-gnu-gcc CXX=aarch64-linux-gnu-g++ ARCH=arm64
   		 or
    	make OS=linux CC=arm-linux-gnueabi-gcc CXX=arm-linux-gnueabi-g++ ARCH=arm


For Windows Builds
------------------

"make" must be installed. It is recommended to install the Cygwin and "make" must be selected to be included in the installation. After the installation, please add the Cygwin bin path to your PATH.

openh264/build/AutoBuildForWindows.bat is provided to help compile the libraries on Windows platform.  
Usage of the .bat script:  

    `AutoBuildForWindows.bat Win32-Release-ASM` for x86 Release build  
    `AutoBuildForWindows.bat Win64-Release-ASM` for x86_64 Release build  
    `AutoBuildForWindows.bat ARM64-Release-ASM` for arm64 release build  
for more usage, please refer to the .bat script help.  

For All Platforms
-------------------

Using make
----------

From the main project directory:
- `make` for automatically detecting architecture and building accordingly
- `make ARCH=i386` for x86 32-bit builds
- `make ARCH=x86_64` for x86 64-bit builds
- `make ARCH=arm64` for arm64 Mac 64-bit builds
- `make V=No` for a silent build (not showing the actual compiler commands)
- `make DEBUGSYMBOLS=True` for two libraries, one is normal libraries, another one is removed the debugging symbol table entries (those created by the -g option)

The command line programs `h264enc` and `h264dec` will appear in the main project directory.

A shell script to run the command-line apps is in `testbin/CmdLineExample.sh`

Usage information can be found in `testbin/CmdLineReadMe`

Using meson
-----------

Meson build definitions have been added, and are known to work on Linux
and Windows, for x86 and x86 64-bit.

See <http://mesonbuild.com/Installing.html> for instructions on how to
install meson, then:

``` shell
meson builddir
ninja -C builddir
```

Run the tests with:

``` shell
meson test -C builddir -v
```

Install with:

``` shell
ninja -C builddir install
```

Using the Source
----------------
- `codec` - encoder, decoder, console (test app), build (makefile, vcproj)
- `build` - scripts for Makefile build system
- `test` - GTest unittest files
- `testbin` - autobuild scripts, test app config files
- `res` - yuv and bitstream test files

Known Issues
------------
See the issue tracker on https://github.com/cisco/openh264/issues
- Encoder errors when resolution exceeds 3840x2160
- Encoder errors when compressed frame size exceeds half uncompressed size
- Decoder errors when compressed frame size exceeds 1MB
- Encoder RC requires frame skipping to be enabled to hit the target bitrate,
  if frame skipping is disabled the target bitrate may be exceeded

License
-------
BSD, see `LICENSE` file for details.
