Mainline Hardware Decoding

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Mainline Hardware Decoding refers to video decoding done using hardware accelerators on the mainline Linux kernel (i.e. what sits in Linus' tree).

On most consumer-oriented SoCs, there is what is referred to as a VPU (Video Processing Unit). The VPU is responsible for power-efficient encoding and decoding of videos. Hardware-accelerated video decoding can be useful to get smoother video playback on your devices, lower power consumption, and lower CPU utilisation. Below is information regarding various hardware PINE64 uses and software that works with it.

Hardware

Here's a table of the current support for different hardware. "In review" means the patch series to enable support has been posted to the mailing lists but is undergoing review, "linux-next" means it has been accepted and staged for the next Linux merge window.

Supported Codecs By SoC

SoC Codec	A64	RK3328	RK3399	RK3566	RK3588
JPEG	No	No	Yes	No	No
MPEG-2	Yes	Yes	Yes	Yes	No
MPEG-4 Part 2/H.263	No	No	No	No	No
VP8	Yes	Yes	Yes	Yes	No
H.264/AVC	Yes	Yes	Yes	Yes a	No
H.265/HEVC	Yes	In review	Patches Exist	No	No
VP9	N/A	Yes	Yes	No	No
AVS2	N/A	N/A	N/A	N/A	No
AV1	N/A	N/A	N/A	N/A	linux-next

Notes

1. only Hantro, not rkvdec2, so with a maximum resolution of 1080p for now

Used SoC By Device

This table provides a quick reference to check which SoC is used in what Pine devices, for ease of navigating the previous table.

SoC	Device(s)
Allwinner A64	PinePhone, PineTab1, Pinebook, PINE A64, PINE A64-LTS, SOPINE
Rockchip RK3328	ROCK64
Rockchip RK3399	PinePhone Pro, Pinebook Pro, ROCKPro64
Rockchip RK3566	Quartz64 Model A and B, SOQuartz, PineTab2
Rockchip RK3588	QuartzPro64

Cedrus

In 2018, Bootlin launched a crowdfunding campaign to bring a open source Allwinner VPU driver to mainline Linux, which came to be called Cedrus. The Cedrus media driver (For Allwinner SOCs such as A64) supported by mainline Linux supports H.264 and H.265 video decoding as of Linux 5.10, and with 5.11 came VP8 decoding support and a H.264 stateless video decoder interface. For more information refer to the Sunxi wiki.

Hantro

The Hantro media driver supports Rockchip and NXP SoCs including the RK3399 used in the Pinebook Pro and RockPro64. In November 2020 it was announced that Bootlin was working on encoding support for the driver.

rkvdec

rkvdec is the video decoding hardware that's developed by Rockchip presumably in house. It's what Rockchip uses for decoding 4K H.264/AVC, VP9 and H.265/HEVC content. The driver in mainline linux for the first generation rkvdec (used in RK3328 and RK3399) supports VP9 and H.264, patches for HEVC support exist but require modification and resubmission to mainline.

RK3566, RK3568 and likely RK3588 use a second generation of rkvdec called rkvdec2. No mainline driver for this exists yet. The rkvdec instance on RK3588 additionally supports the AVS2 video codec.

rkdjpeg

rkdjpeg is Rockchip's in-house hardware accelerated JPEG decoder. It can be found on the RK3566 and RK3568 as well as the RK3588.

No mainline driver exists for it so far.

Software

GStreamer

H.264, H.265, MPEG-2, VP8, VP9 and AV1 video decoding is possible when using GStreamer's command line tools, or an application utilizing it such as Clapper or µPlayer. µPlayer includes a indicator of when hardware acceleration is properly working and in use.

Using gst-launch

To test out hardware decoding from the command line, gst-launch-1.0 may be used. An example pipeline to demux, hardware decode and display H.264 video in an MP4 container would be as follows:

gst-launch-1.0 filesrc location=yourfilehere.mp4 ! qtdemux ! v4l2slh264dec ! videoconvert ! autovideosink

To do the same for a VP8 WebM file, one may use:

gst-launch-1.0 filesrc location=yourfilehere.webm ! matroskademux ! v4l2slvp8dec ! videoconvert ! autovideosink

Depending on your GStreamer version and your GStreamer's build configuration, the following may be available as well: v4l2slmpeg2dec, v4l2slav1dec, v4l2slvp9dec and v4l2slh265dec.

On platforms with a 2D accelerator (such as Rockchip's RGA) that is supported by v4l2, one may use v4l2convert instead of videoconvert to also hardware accelerate the pixel format conversion.

FFmpeg

Mainline FFmpeg currently lacks the necessary patches to use the v4l2-requests based API, but a fork that can utilise it exists. Fedora users can install precompiled binaries from a dedicated repository by one of the Fedora maintainers.

To build it, use something like

git clone -b v4l2-request-n6.0 https://github.com/jernejsk/FFmpeg.git
cd FFmpeg
./configure --enable-v4l2-request --enable-libudev --enable-libdrm --enable-gnutls --prefix=/some/install/prefix/here
make -j$(nproc)

After compiling, you can install it into your specified prefix with

make install

And then modify your PATH to include the prefix's bin directory.

With the patched ffmpeg, you can utilise hardware decoding using the -hwaccel drm parameter, e.g.:

ffmpeg -hwaccel drm -i input.mp4 -f null - -benchmark

to measure how fast it decodes.

mpv

mpv v0.35 or later, built against the aforementioned FFmpeg fork, can be used to play back videos with hardware accelerated decoding. The hardware decoder path features interop with the GPU output, saving an expensive copyback operation. You can utilise the hardware decoding with e.g.:

 mpv --hwdec=drm video

In mpv versions prior to 0.35, you can use the copyback hwdec with:

 mpv --hwdec=drm-copy video

To build an mpv against the FFmpeg in your prefix, you can run

 PKG_CONFIG_PATH="/path/to/your/ffmpeg/prefix/lib/pkgconfig:$PKG_CONFIG_PATH" meson setup build
 ninja -C build

HEVC on Linux for RK3399

LibreELEC maintains patches applicable to mainline Linux that, almong other things, add HEVC decode to rkvdec. Patches linux-0011-v4l2-from-list.patch, linux-1001-v4l2-rockchip.patch, linux-2000-v4l2-wip-rkvdec-hevc.patch and linux-2001-v4l2-wip-iep-driver.patch from commit 269fd4f can be applied to Linux 6.5.2 (tested) and are sufficient to use hardware HEVC decode on the RK3399.

More Resources

• Megi's Cedrus Information
• HW accelerated GStreamer playback on the PinePhone
• HW accelerated Clapper video player on the PinePhone

See Also

• Mainline Hardware Encoding