Decoding videos in Firefox with VA-API

Outlook

Use the turbostat tool to determine whether the energy consumption when playing videos using VA-API is now lower (see the "Consumption Display" box). Table 1 shows the averaged values when playing a video via the mpv media player and for Firefox on a Dell Latitude E7250 with the Broadwell chipset (Intel Core i5 5300U). While mpv obviously benefits from the optimized decoder chip, the savings in Firefox with WebRender are somewhat lower. PowerTOP reports a discharge rate of 7.60W (Figure 3) for VA-API; without it, the system draws 8.56W of power from the notebook battery when playing the video in the browser (Figure 4).

Table 1

Energy Consumption

Test

PkgWatt

CorWatt

GFXWatt

PowerTOP

mpv (hwdec=no)

4.08W

1.72W

0.15W

7.87W

mpv (hwdec=vaapi)

2.78W

0.74W

0.09W

6.32W

Nightly (plain)

5.20W

3.15W

0.04W

8.56W

Nightly (VA-API)

3.73W

1.45W

0.12W

7.60W

Consumption Display

The turbostat tool is part of the Linux kernel and is built into the linux-cpupower package on Debian. Other distributions, such as Arch Linux, store the program in the turbostat standalone package. The application reads the energy consumption statistics provided by the computer system. The command in Listing 7 displays the power consumption values at intervals of three seconds. PkgWatt stands for package (i.e., the chipset), CorWatt for the processor, GFXWatt for the graphics card, and RAMWatt for the main memory. Press Ctrl+C to exit turbostat and return to the prompt.

Figure 3: The Firefox web browser can also use hardware acceleration, but support for this function is not yet standard under Linux.
Figure 4: Without VA-API, the system draws nearly 1W more power from the laptop's battery when playing back the video in Firefox's current nightly build.

Thanks to Red Hat's commitment, Firefox on Linux will soon use the graphics card for decoding videos by default, allowing Firefox to finally catch up with the Microsoft Windows 10 version in terms of functionality. Default VA-API integration removes another obstacle to achieving the year of the Linux desktop (if that year ever happens).

As videoconferencing needs increase, encoding videos (of yourself) becomes just as important as decoding the received video data. Many image streams are encoded with VP8, which many graphics cards support. Firefox 80 or 81 can use VA-API for WebRTC [12] after enabling media.ffmpeg.low-latency.enabled in about:config. Hopefully, Firefox will soon enable VA-API integration by default, doing away with all of the manual work.

Listing 7

Power Consumption Values

§§number
$ turbostat --quiet -i 3 -s 'PkgWatt,CorWatt,GFXWatt,RAMWatt'
PkgWatt CorWatt GFXWatt RAMWatt
4.21 1.55 0.13 1.02
4.21 1.55 0.13 1.02
[...]

Infos

  1. ASIC: https://en.wikipedia.org/wiki/Application-specific_integrated_circuit
  2. VA-API: https://en.wikipedia.org/wiki/Video_Acceleration_API
  3. WebRender: https://github.com/servo/webrender/wiki
  4. WebRender on Linux: https://wiki.mozilla.org/Platform/GFX/WebRender_Where#Linux
  5. "Firefox on Fedora finally gets VA-API on Wayland": https://mastransky.wordpress.com/2020/06/03/firefox-on-fedora-finally-gets-va-api-on-wayland
  6. FFmpeg: https://ffmpeg.org
  7. "Add VA-API decode path to bundled ffvpx": https://bugzilla.mozilla.org/show_bug.cgi?id=1660336
  8. h264ify: https://addons.mozilla.org/en-US/firefox/addon/h264ify
  9. enhanced-h264ify: https://addons.mozilla.org/en-US/firefox/addon/enhanced-h264ify
  10. Mozilla Bugzilla: https://bugzilla.mozilla.org
  11. Download Firefox: https://www.mozilla.org/en-US/firefox/channel/desktop/
  12. "Use VA-API decoder with WebRTC": https://bugzilla.mozilla.org/show_bug.cgi?id=1646329

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