Cross compiling FFMPEG libs

[Michael IV]

Hi All. I need a little advice before I invest my time int this adventure. I need to decode h264 streams in a browser (I don't want to use HLS,MPEG DASH or other high latency techs). And I would like (ideally) to use API from libavcodec,libavformat and the rest of FFMPEG libs.

I would like to know if emscripten has any restriction which may prevent me from accomplish this task. I played around with emscripten a couple of 

years ago and today I am not really aware of its state. For example, FFMPEG libs are multi-threaded (especially encoders/decoders). Does emscripten

allow threaded C/C++ code? What are additional underwater stones I can get while trying such a thing? 

Thanks,

Michael.

[Brion Vibber]

On Mon, Oct 16, 2017 at 2:15 PM, Michael IV <explo...@gmail.com> wrote:

Hi All. I need a little advice before I invest my time int this adventure. I need to decode h264 streams in a browser (I don't want to use HLS,MPEG DASH or other high latency techs). And I would like (ideally) to use API from libavcodec,libavformat and the rest of FFMPEG libs.

You might want to start with https://github.com/Kagami/ffmpeg.js -- oriented around encoding, but the build of the libraries is the important part... Last I tried a couple years ago, OpenH264 also builds with emscripten but I haven't tested it in a while.

You might also find benefit from some parts of my ogv.js WebM/Ogg player (no H.264 included yet due to patent concerns), in particular you may find yuv-canvas useful for accelerating YUV-RGB conversion and display with WebGL: https://github.com/brion/yuv-canvas

 

I would like to know if emscripten has any restriction which may prevent me from accomplish this task. I played around with emscripten a couple of 

years ago and today I am not really aware of its state. For example, FFMPEG libs are multi-threaded (especially encoders/decoders). Does emscripten

allow threaded C/C++ code? What are additional underwater stones I can get while trying such a thing? 

Threading with pthreads is supported on browsers with SharedArrayBuffer support - see https://kripken.github.io/emscripten-site/docs/porting/pthreads.html - but there are difficulties:

* not all browsers have SharedArrayBuffer yet

* threading not yet support for WASM builds

* threading with asm.js builds requires re-parsing JavaScript on every thread, which increases memory requirements and load times

* some browsers de-optimize threaded asm.js code, which can make it run slower than single-threaded builds!

* pthreads mode is currently incompatible with the 'modular' mode used to make the compiled code more reusable - I have a patch https://github.com/kripken/emscripten/pull/5016 which may or may not still apply cleanly.

My recommendation is to make a single-threaded build for now, and wait for threading to arrive in WASM before trying to deploy threaded emscripten code.

Good luck!

-- brion

[Michael IV]

Thanks man for this extensive info! The multi-threading is indeed the main concern here. I am afraid that single threaded decoding will not be optimal for my needs. I already checked Broadway.js .But it 

supports only h264 base profile and yes,it is slow when it comes to decode HD at 60 or more FPS. So I need to see how to approach this problem.

Many thanks for the info again.

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[Alon Zakai]

Note that threads in wasm are very high priority. Should be testable soon.

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