https://github.com/Yahweasel/libav.js

This is a compilation of the libraries associated with handling audio and video in ffmpeg—libavformat, libavcodec, libavfilter, libavutil, libswresample, and libswscale—for emscripten, and thus the web.
https://github.com/Yahweasel/libav.js

Last synced: 19 days ago
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This is a compilation of the libraries associated with handling audio and video in ffmpeg—libavformat, libavcodec, libavfilter, libavutil, libswresample, and libswscale—for emscripten, and thus the web.

• Host: GitHub
• URL: https://github.com/Yahweasel/libav.js
• Owner: Yahweasel
• License: other
• Created: 2019-08-21T20:04:18.000Z (over 5 years ago)
• Default Branch: master
• Last Pushed: 2024-10-25T02:26:54.000Z (about 2 months ago)
• Last Synced: 2024-10-25T05:52:47.321Z (about 2 months ago)
• Language: JavaScript
• Homepage:
• Size: 7.8 MB
• Stars: 345
• Watchers: 6
• Forks: 27
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.md

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README

        
# libav.js

This is a compilation of the libraries associated with handling audio and video

in FFmpeg—libavformat, libavcodec, libavfilter, libavutil and libswresample—for

WebAssembly and asm.js, and thus the web, as well as the `ffmpeg` and `ffprobe`

CLIs themselves. It is compiled via emscripten, is highly customizable, and has

a ruthless commitment to correct licensing.

In short, this is a pure JavaScript and WebAssembly system for low-level audio

and video encoding, decoding, muxing, demuxing, and filtering.

FFmpeg is released under the LGPL. Therefore, if you distribute this library,

you must provide sources. The sources are included in the `sources/` directory

of the compiled version of libav.js.

In order to reduce license-header Hell, the small amount of wrapper functions

provided by libav.js are all released under the so-called “0-clause BSD”

license, which does not require that the license text itself appear in

derivative works. Built libraries have their correct license headers.

This file is the main README for using and building libav.js, and should be

sufficient for many users. More detail on specific concepts is provided in other

files:

 * [API.md](docs/API.md) describes the libav.js-specific parts of the API.

 * [CONFIG.md](docs/CONFIG.md) describes the configuration system and how to

   create your own configuration of libav.js.

 * [IO.md](docs/IO.md) describes the various I/O modes provided by libav.js.

 * [TESTS.md](docs/TESTS.md) describes the testing framework.

## Using libav.js

libav.js builds are available on

[GitHub](https://github.com/Yahweasel/libav.js/releases) and in NPM. Include

dist/libav-`version`-`variant`.js to use libav.js. The variants are discussed

below.

The simplest way to use libav.js is to include it from a CDN. libav.js uses Web

Workers by default, and Web Workers cannot be loaded from a different origin, so

if you load it from a CDN, you must disable its own loading of workers. As such,

it's only recommended to use libav.js from a CDN if you're already *in* a

worker, and thus don't need sub-workers. Nonetheless, the following is a simple

example of using libav.js from a CDN in the browser thread:

```html

    

        

        (async function() {

            const libav = await LibAV.LibAV({noworker: true});

            await libav.writeFile("tmp.opus", new Uint8Array(

                await (await fetch("exa.opus")).arrayBuffer()

            ));

            const [fmt_ctx, [stream]] = await libav.ff_init_demuxer_file("tmp.opus");

            const [, c, pkt, frame] = await libav.ff_init_decoder(stream.codec_id, stream.codecpar);

            const [, packets] = await libav.ff_read_multi(fmt_ctx, pkt);

            const frames = await libav.ff_decode_multi(c, pkt, frame, packets[stream.index], true);

            alert(`Got ${frames.length} audio frames!`);

        })();

        

    

```

Here's a better example, using libav.js locally:

```html

    

        

        (async function() {

            const libav = await LibAV.LibAV();

            await libav.writeFile("tmp.opus", new Uint8Array(

                await (await fetch("exa.opus")).arrayBuffer()

            ));

            const [fmt_ctx, [stream]] = await libav.ff_init_demuxer_file("tmp.opus");

            const [, c, pkt, frame] = await libav.ff_init_decoder(stream.codec_id, stream.codecpar);

            const [, packets] = await libav.ff_read_multi(fmt_ctx, pkt);

            const frames = await libav.ff_decode_multi(c, pkt, frame, packets[stream.index], true);

            alert(`Got ${frames.length} audio frames!`);

        })();

        

    

```

It's also possible to use libav.js from Node.js, though this isn't a good idea,

since you can presumably use a native version of FFmpeg's libraries. The Node

interface is only provided for internal testing.

Use `.dbg.js` instead of `.js` for a non-minified, more debuggable version. Use

`.mjs` for the ES6 module version. Use `.dbg.mjs` for both. You don't need any

combination; e.g., if you only intend to use imports, you do not need any `.js`

files.

libav.js exposes a global variable, `LibAV`, for all API access. If importing as a

module, `LibAV` is the default export.

For certain unusual loading situations, you can set the `LibAV` global variable

before importing. In particular, if the base directory (directory in which

libav's files are located) can't be detected for some reason, then you must set

`LibAV.base` to the correct base. `LibAV.base` does not need to be a full URL,

but should be if loading from another origin.

Bundlers have further concerns. To use libav.js with a bundler, see the section

on bundlers below.

`LibAV.LibAV` is a factory function which returns a promise which resolves to a

ready instance of libav. The factory function and libav instance methods are

documented in [API.md](docs/API.md).

## Which files do I need?

You need the main entry file and at least one target, for a minimum of three

files, but you should probably include several others.

The main entry file is named as follows: `libav--.js`. You

only need the variant you intend to use. The debug version is named

`libav--.dbg.js`, and you can use that in place of the

original, but it is not required. If using ES6 modules, use `mjs` in place of

`js`.

That entry file will load a target based on the environment it's loaded in and

the options used to load it, as described above. The supported targets are

asm.js, plain WebAssembly, and threaded WebAssembly. It is harmless to include

all of them, as users will not download all of them, only the ones they use.

But, you may also include only those you intend to use. In every case, there is

a `.dbg.js` equivalent which is only needed if you intend to use debug mode.

 * asm.js: Named `libav--.asm.js`. No modern browser excludes

   support for WebAssembly, so this is probably not necessary.

 * Plain WebAssembly: Named `libav--.wasm.js` and

   `libav--.wasm.wasm`. Used in most situations.

 * Threaded WebAssembly: Named `libav--.thr.js`, `.thr.wasm`,

   and `.thr.worker.js`. Used only when threading is supported by the browser

   *and* `yesthreads` is set. If you don't intend to use threads (set

   `yesthreads`), it is safe to exclude this. Used only when threads are

   activated and supported.

At a minimum, it is usually sufficient to include only the `.js`, `.wasm.js`,

and `.wasm.wasm` files. To include threads, you must also include `.thr.js` and

`.thr.wasm`. Again, use `mjs` instead of `js` if using ES6 imports.

The file `libav.types.d.ts` is a TypeScript types definition file, and is only

needed to compile TypeScript code with support for libav.js's types. It should

never be necessary to distribute.

Note that, independently of what files are available to end users, *you are

contractually obligated to release the source code of libav.js and all of its

dependencies* if you provide the compiled version. If you are using a compiled,

released version, it is sufficient to provide the `sources` directory.

libav.js is published to NPM as `libav.js`, and each released variant is

published in a much smaller NPM package as `@libav.js/variant-`. The

CDN example above uses the `@libav.js/variant-default` package, for example.

### Why the version number in the filenames?

Caching is Hell.

`libav-.*` is also available in the releases and repository, but you're

highly recommended *not* to use this name on any web installation, as caching

will cause strange nonsense to happen. Use a full versioned name to avoid

caching madness.

## Devices and asynchrony

Emscripten's implementation of an in-memory filesystem has severe limitations.

You're recommended to use virtual devices, implemented by `libav.js`, for most

I/O. See [IO.md](docs/IO.md) for more details. libav.js itself imposes no

restriction on file sizes so long as you use asynchronous, device-backed I/O

(thus, the only restriction to size is JavaScript's number type).

ffmpeg was never designed to work asynchronously, and was only designed to work

with blocking I/O. Still, it's possible to use libav.js with asynchronous input

through these devices.

## TypeScript

Type definitions for libav.js are provided by `libav.types.d.ts`. You can

either copy this file and import it:

```typescript

import type LibAVJS from "./libav.types";

declare let LibAV: LibAVJS.LibAVWrapper;

```

or import it from the npm package:

```typescript

import type LibAVJS from "libav.js";

declare let LibAV: LibAVJS.LibAVWrapper;

```

## Variants and Building libav.js

With all of its bells and whistles enabled, FFmpeg is pretty large. So, I

disable most bells and most whistles and build specific versions with specific

features.

The default variant, `libav--default.js`, includes support for the most

important (and timeless) audio codecs and formats: Opus, FLAC, and wav, in WebM,

ogg, FLAC, or wav containers. It also has a set of common audio filters.

Built-in variants are created by combining “configuration fragments”. You can

find more on configuration fragments or making your own variants in

[CONFIG.md](docs/CONFIG.md).

Use `make build-`, replacing `` with the variant name, to

build another variant.

Most of the variants provided in the repository are also built and available in

NPM and as binary releases. The notable exception is all variants that include

codecs controlled by the Misanthropic Patent Extortion Gang (MPEG). They are not

built by default, and if you have any sense, you should not use them. MPEG is a

cancer on the digital media ecosystem.

The included variants and their codecs and formats are:

 * default, default-cli: Opus (via libopus), FLAC, and wav in ogg, WebM, FLAC,

   and wav containers, plus audio filters. The `-cli` subvariant additionally

   includes the CLI (`ffmpeg` and `ffprobe` functions).

 * opus, opus-af: Opus in ogg or WebM. `-af` additionally includes audio

   filters.

 * flac, flac-af: FLAC in ogg or FLAC. `-af` additionally includes audio

   filters.

 * wav, wav-af: PCM wav (16-bit or 24-bit) in wav. `-af` additionally includes

   audio filters.

 * obsolete: Same as default with the addition of two obsolete codecs, Vorbis

   (via libvorbis) and MPEG-1 Layer 3 (MP3) (via libmp3lame). Also includes the

   MP3 container format.

 * webm, webm-vp9¹, webm-cli, webm-vp9-cli¹: Same as default with the addition

   of VP8 (via libvpx) and video filters. `-vp9` additionally includes VP9,

   `-cli` additionally includes the CLI. `-vp9` is separated due to the rather

   significant size of the VP9 codec.

 * webcodecs, webcodecs-avf: Designed to serve as a demuxer/muxer for codecs

   supported by WebCodecs. Pairs well with

   [libavjs-webcodecs-bridge](https://github.com/Yahweasel/libavjs-webcodecs-bridge).

   Includes codecs for Opus, FLAC, and wav. Includes *parsers* (but not codecs)

   for AAC, VP8, VP9, AV1, H.264, and H.265. Includes the ogg, WebM, MP4, FLAC,

   and wav formats. This means that it can demux files including, e.g., H.264,

   but cannot decode the frames. If your WebCodecs supports H.264, you can then

   use it to decode. `-avf` additionally includes audio and video filters.

 * vp8-opus, vp8-opus-avf: VP8 and Opus in WebM (or ogg). `-avf` additionally

   includes audio and video filters.

 * vp9-opus¹, vp9-opus-avf¹: VP9 and Opus in WebM (or ogg). `-avf` additionally

   includes audio and video filters.

 * av1-opus¹, av1-opus-avf¹: AV1 (via libaom) and Opus in WebM (or ogg). Note

   that AV1 support is currently so slow in WebAssembly even with threads that

   these variants are effectively unusable. `-avf` additionally includes audio

   and video filters.

 * aac², aac-af²: Reprobate codec AAC in MP4 or AAC/ADTS. `-af` additionally

   includes audio filters.

 * h264-aac², h264-aac-avf²: Reprobate codec H.264 (via libopenh264) and

   reprobate codec AAC in MP4 (or AAC/ADTS). `-avf` additionally includes audio

   and video filters.

 * hevc-aac², hevc-aac-avf²: Reprobate codec H.265 (decoding only) and reprobate

   codec AAC in MP4 (or AAC/ADTS). `-avf` additionally includes audio and video

   filters.

¹ These builds are not included in the full NPM release for space reasons, but are

  included in GitHub releases, and are available on NPM as

  @libav.js/variant-``, e.g. `@libav.js/variant-vp9-opus`.

² Includes technologies patented by the Misanthropic Patent Extortion Gang

  (MPEG). You should not build these, you should not use these builds, and you

  should not support this organization which works actively against the common

  good.

This is intentionally designed so that you can add new variants without needing

to patch anything that already exists. If you want to create your own variants,

see [CONFIG.md](docs/CONFIG.md).

You can also build against different versions of FFmpeg than the version built

by default. To build against, for instance, FFmpeg 4.3.6, use `make

FFMPEG_VERSION_MAJOR=4 FFMPEG_VERSION_MINREV=3.6`. Note that you *must* use

`FFMPEG_VERSION_MAJOR` and `FFMPEG_VERSION_MINREV`, not just `FFMPEG_VERSION`,

because `FFMPEG_VERSION_MAJOR` is used to direct the process of patching FFmpeg.

libav.js should generally build against any version of FFmpeg in the 4, 5, or 6

series, but is not heavily tested against older versions; you should use the

default version unless you have some specific compatibility issue that forces

you to use a different version.

## Size

FFmpeg is big, so libav.js is big. But, it's not ludicrous; the WebAssembly is

usually between 1.5 and 3 MiB for fairly complete builds, and the asm.js is about

double that.

You can estimate the size of variants based on the size of the constituent

fragments. As of version 5.0.6.1.1, an empty build is approximately 589KiB

(WebAssembly). The sizes of each additional fragment can be found in

[fragment-sizes.csv](docs/fragment-sizes.csv). The data in that CSV file can be

recreated by `tools/fragment-sizes.sh`, but note that the CSV file in the

repository is after further processing (in particular, normalizing to KiB and

subtracting away the empty size).

The asm.js versions are much bigger, but will not be loaded on

WebAssembly-capable clients.

The wrapper (“glue”) code is about 292KiB, but is highly compressible.

## Performance

Generally speaking, the performance of audio en- and decoding is much faster

than real time, to the point that it's simply not a concern for most

applications. The author of libav.js regularly uses libav.js in live audio

systems.

Video is a different story, of course.

Video is nowhere near as slow as you might imagine. On reasonable systems,

faster-than-real-time performance for decoding of up to 1080P is achievable if

you use a threaded version of libav.js. If you're willing to use older, simpler

video codecs and lower-resolution video, even real-time *encoding* is possible.

But, for complex codecs, real-time en/decoding is not realistic. One of the

revolutions of video en/decoding is hardware en/decoding, and libav.js cannot do

that, so its performance ceiling is already low.

Muxing and demuxing are bound by I/O time, not software performance. libav.js

will always mux or demux faster than you can use the data.

## libav.js and WebCodecs

On some modern browsers, the WebCodecs API is availble for hardware-accelerated

(or at least, CPU-specific) en/decoding of various codecs. When it is available,

it is better to use it than libav.js. However, WebCodecs does not mux or demux,

and which codecs it supports varies based on the moods of its implementor (if it

is even present), so generally, it is necessary to support WebCodecs but fall

back to libav.js when necessary.

To make this easier, two companion projects to libav.js are provided that

connect it to WebCodecs:

 * [libavjs-webcodecs-polyfill](https://github.com/ennuicastr/libavjs-webcodecs-polyfill)

   is a polyfill for the WebCodecs API using libav.js. Even if WebCodecs exists

   on your browser, this polyfill allows the user to guarantee a certain set of

   supported codecs; any codecs not supported by the built-in WebCodecs can

   simply fall back to libav.js, using only one API.

 * [libavjs-webcodecs-bridge](https://github.com/Yahweasel/libavjs-webcodecs-bridge)

   is a bridge between libav.js and WebCodecs, converting between the two data

   formats. This makes it easy to use libav.js for demuxing and WebCodecs for

   decoding, or WebCodecs for encoding and libav.js for muxing. Of course, the

   WebCodecs used with the bridge can easily be the polyfill if needed.

## Bundlers

Generally speaking, because libav.js needs to adjust its loading procedure based

on the environment it's being loaded in, it's not a good idea to bundle

libav.js. However, if you have to bundle it, it can be done if necessary.

libav.js has a frontend (`libav--.js`), a factory

(`libav--.wasm.js` or `.thr.js`), and, if using WebAssembly, a

backend (`libav--.wasm.wasm` or `.thr.wasm`). Any of these can

be overridden, and any of them can be object URLs to bundle everything, though

this will destroy libav.js's ability to load the correct version for the system.

To override the frontend, simply load a different frontend!

To override the factory, you have two choices:

 * Pass `toImport`, a string, to `LibAV.LibAV`'s options, e.g.,

   `LibAV.LibAV({toImport: "libav-but-better.wasm.js"})`.

 * Load the factory yourself, and pass the factory function as the `factory`

   option to `LibAV.LibAV`, e.g., `LibAV.LibAV({factory: LibAVFactory})`. By

   default, the factory function is exported as `LibAVFactory`, or for ES6

   modules, it is the default export of the module.

To override the backend, you can pass the full URL (or object URL) to the

WebAssembly as the option `wasmurl` to `LibAV.LibAV`, e.g.,

`LibAV.LibAV({wasmurl: URL.createObjectURL(...)})`.

Be careful about which versions of things you bundle. The ES6 module version of

libav.js assumes that it will actually *be* an ES6 module, and so will be able

to use, e.g., `import`. If your bundler transforms it into a non-ES6 module, you

must explicitly tell it to import some other way by passing the option `noes6`

to `LibAV.LibAV`, e.g., `LibAV.LibAV({noes6: true})`. Also, if your bundler

converts the ES6 frontend to non-ES6 and you intend to explicitly specify

`toImport`, you must specify the *non-ES6* factory.