add wasm build support

[Yuhengwe1]

add Webassembly build support for openh264.

our build & test environment:

• emcc version 3.16.0
• node.js version v16.16.0
• chrome version 105.0.5195.127

build command

emmake make ARCH= OS=wasm EMFS=nodefs

several build flags for wasm:

• EMFS=nodefs|memfs : select file system to use
• WASMDEBUG=True : when linking, preserve function names in compiled code

test openh264 wasm with local files

h264enc.js, h264enc.wasm, h264dec.wasm, h264dec.wasm will appear in main project dir.

using MEMFS

when build, set EMFS=memfs to package files needed in encoder or decoder test.

for now, emcc with preload all files under testbin/workload

in MEMFS all files will exist strictly in-memory, and any data written to them is lost when web page is reloaded.

to test h264enc.js or h264dec.js in chrome, start chrome with:

chrome.exe --enable-features=SharedArrayBuffer

using NODEFS

set EMFS=nodefs when build.

NODEFS only works for node.js environment, it provides direct access to the local file system.

for now, we mount the main project dir into NODEFS.

run test like this:

node h264enc.js testbin/welsenc_vd_1d_wasm_nodefs.cfg

WIP

we are now optimizing several hotspot functions with wasm intrinsic, updates will be added into this branch.

welcome review!

[Yuhengwe1]

could anyone help code review? @jrmuizel @GuangweiWang

[jrmuizel]

Can you also add github actions support for building this so that it gets tested?

[jrmuizel]

What is this for?

[Yuhengwe1]

This is for test in browser environment. All the files needed in test should be put under testbin/workload

Maybe I need to delete all the files under testbin/workload ?

[jrmuizel]

Why is the string(CWD) + needed?

[Yuhengwe1]

This is for the Emscripten File System

node.js environment for example, we map the main project dir to /workload in virtual filesystem.

After the mount we can run h264enc.js like: node h264enc.js testbin/xxx.cfg

The string(CWD) + add the path prefix. Without it we may need to run h264enc.js like node h264enc.js workload/testbin/xxx.cfg

[jrmuizel]

Why map the main project dir to /workload instead of just the /?

[Yuhengwe1]

Yes, I tried to mount host dir ./ to / in virtual FS for nods.js env, but this will cause error.

In browser env, packaging all the main will lead to longer file reading time.

[Yuhengwe1]

Can you also add github actions support for building this so that it gets tested?

ok, will try to add workflow for wasm

[mstorsjo]

Couldn't you avoid duplicating all this by just setting EXEEXT = .html?

[Yuhengwe1]

Workflow for wasm build test added.

I tried encoder_binary_comparison on my local machine, but got SHA value mismatch in one of the test cases(Zhling_1280x720.264).

Similar SHA value mismatch occurred in unit test: ThreadDecodeFile/ThreadDecoderOutputTest.CompareOutput, the wasm version passed 7/39 cases.

I want to know, are the SHA values of codec results fixed in different build environment?

[Bessonov]

@jrmuizel @GuangweiWang A friendly remainder about open questions above 👍