# Libva Rust wrapper

Rust wrapper for libva. Provides safe libva abstractions for use within Rust code using its own
bindgen-generated bindings.

This crate is used as part of the VirtIO Video VA-API backend. VA-API uses the GPU to perform the
actual decoding/encoding of frames. In doing so, it frees the CPU for other uses and reduces power
usage in the system. Hardware accelerated media workflows also tend to be faster than their software
counterparts.

Note: This create requires the native [libva](https://github.com/intel/libva) library at link time.
It also requires a VA-API driver to be installed on the system. The VA-API driver to use depends on
the underlying hardware, e.g.: the implementation for Intel hardware is in
[intel-media-driver](https://github.com/intel/media-driver), whereas AMD hardware will depend on
[Mesa](https://gitlab.freedesktop.org/mesa/mesa).

An easy way to see whether everything is in order is to run the `vainfo` utility. This is usually
packaged with `libva-utils` or as a standalone package in some distributions. `vainfo` will print
the VA-API version, the driver string, and a list of supported profiles and endpoints, i.e.:

```
vainfo: VA-API version: 1.13 (libva 2.13.0)
vainfo: Driver version: Intel iHD driver for Intel(R) Gen Graphics - 22.2.2 ()
vainfo: Supported profile and entrypoints
      VAProfileNone                   : VAEntrypointVideoProc
      VAProfileNone                   : VAEntrypointStats
      VAProfileMPEG2Simple            : VAEntrypointVLD
      VAProfileMPEG2Simple            : VAEntrypointEncSlice
      VAProfileMPEG2Main              : VAEntrypointVLD
      VAProfileMPEG2Main              : VAEntrypointEncSlice
      VAProfileH264Main               : VAEntrypointVLD
      etc
```

For decoding, the desired profile must be supported under `VAEntrypointVLD`. For example, in order
to decode VP8 media, this line must be present in the output of `vainfo`:

```
      VAProfileVP8Version0_3          : VAEntrypointVLD
```

Whereas to decode H264 Main profile media, this line must be present:

```
      VAProfileH264Main               : VAEntrypointVLD
```

For more information on VA-API and its usage within ChromeOS, see
[this guide](https://chromium.googlesource.com/chromium/src/+/master/docs/gpu/vaapi.md).

For a brief introduction on how to use this crate, see the `libva_utils_mpeg2vldemo` test under
src/lib.rs.