This document records all notable changes made to Cobalt since the last release.
Deleted deprecated --webdriver_listen_ip switch.
--webdriver_listen_ip switch was deprecated in Cobalt 22 in favor of
C++14 is required to compile Cobalt 22.
Cobalt code now requires C++14-compatible toolchains to compile. This requirement helps us stay updated with C++ standards and integrate third-party libraries much easier. C++17 support is recommended, but not yet required to compile Cobalt.
Updated lifecycle handling to support concealed mode.
Cobalt now supports a “concealed” state when used with Starboard 13 or later. See (doc/lifecycle.md)[doc/lifecycle.md] for more information.
window.navigator.onLine property and its change events are added.
To improve user experience during network connect/disconnect situations and enable auto-reconnect, Cobalt added web APIs including Navigator.onLine property and its change events. To enable using the property and events on a platform, the platform's Starboard must implement these new Starboard APIs: SbSystemNetworkIsDisconnected(), kSbEventTypeOsNetworkDisconnected Starboard event, kSbEventTypeOsNetworkConnected Starboard event.
Added support for User Agent Client Hints.
User agent client hints (https://wicg.github.io/ua-client-hints/#interface) is now supported. This does not impact the existing User Agent string.
Added support for Performance Timeline Web API.
To facilitate metrics for Cobalt performance, the following web APIs are now supported:
Additionally, a subset of the following web API is also supported:
Added support for TextEncoder and TextDecoder Web APIs.
The following Web APIs are now supported:
Added support for rendering HTML elements with different border styles.
Previously, Cobalt only supported borders on elements which used the same border style (e.g. solid) for all sides. This is now fixed.
ICU rebased to version 68.
Additionally, ICU data is now packaged as a single file instead of individual files for each locale; this saves about 2MB of storage space compared to the previous version.
Fixed instances where system ICU headers were included.
To maintain consistency, only ICU headers from the included version of ICU are used.
Added support for multiple splash screens.
Added Cobalt extension to handle Media Session Web API.
This new Cobalt extension allows platform-specific support for Media Session controls.
This configuration was only relevant for SpiderMonkey, which has been removed.
Removed Cobalt's custom window.console object.
This was only used with SpiderMonkey. V8 has its own handling of the console object so the Cobalt version is no longer needed.
Cobalt now uses only built-in git commands for development, and the setup guide has been changed to reflect that.
Started migration from GYP to GN.
The starboard layer can now be built using GN. See
We will only support V8 from now on. For platforms without Just-In-Time compilation ability, please use JIT-less V8 instead. Overriding
cobalt_enable_jit environment variable in
gyp_configuration.py will switch V8 to use JIT-less mode. V8 requires at least Starboard version 10.
Runtime V8 snapshot is no longer supported
V8 has deprecated runtime snapshot and mandated build-time snapshot, Cobalt adopts this change as well. Build-time snapshot greatly improves first startup speed after install and is required for JIT-less mode.
scratch_surface_cache_size_in_bytes is removed.
Because it never ended up being used,
scratch_suface_cache_size_in_bytes has been removed. This had only been implemented for possible performance gains, but was found to have inconsistent improvement.
Disabling spdy is no longer supported.
Since updating to Chromium m70, we have enabled spdy by default. We can no longer support disabling it, so we are removing the GYP configuration variable entirely.
DevTools rebased to Chromium 80; requires nodejs to build.
DevTools has been updated to match Chromium m80 (3987), taken from the ChromeDevTools repo. This update now uses Rollup.js to build ES6 modules for the various “applications” comprising the DevTools frontend, requiring nodejs to be installed to build Cobalt (sudo apt-get install nodejs).
DevTools and WebDriver listen to ANY interface, except on desktop PCs.
DevTools and WebDriver servers listen to connections on any network interface by default, except on desktop PCs (i.e. Linux and Win32) where they listen only to loopback (localhost) by default. A new
--dev_servers_listen_ip command line parameter can be used to specify a different interface for both of them to listen to.
DevTools shows asynchronous stack traces.
When stopped at a breakpoint within the handler function for an asynchronous operation, the call stack in DevTools now shows both the current function as well as the function where the asynchronous operation was initiated.
Optimized network buffer management and notification handling.
Reduced unnecessary buffer copying during network downloading which results in the reduction of CPU usage on both the NetworkModule thread and the MainWebModule thread. Peak memory usage during downloading is also reduced. Also reduced redundant notifications from the NetworkModule thread to the MainWebModule thread on downloading progresses.
Web Extension support is deprecated.
Web Extension support is deprecated. Please migrate to Platform Services instead. This is part of an effort to move away from injecting compile-time modules into the Cobalt layer in favor of using runtime extensions provided by the Starboard layer.
Improved support of “dir” global DOM attribute.
Although the “dir” attribute was supported in previous versions, it only impacted text direction. Now layout will also abide by the “dir” attribute. Additionally, dir=“auto” is now supported. These changes are intended to support right-to-left (RTL) languages.
NOTE: The CSS “direction” property is explicitly not supported since the spec recommends using the “dir” attribute instead.
Local font package switched to WOFF2 format.
All packaged fonts that were previously in TTF format are now converted to WOFF2. This change compresses the default Cobalt font package size by about 38% (14MB) and overall Cobalt package size with a standard font configuration by about 21%. TTF and other font formats continue to be supported for remotely downloaded fonts and system fonts.
In order to support native WOFF2 font loading, we've also updated our FreeType version from 2.6.2 to 2.10.2. For a full list of FreeType updates included in this change, visit www.freetype.org.
Added support for Lottie animations.
Cobalt can now embed and play Lottie animations (https://airbnb.design/lottie/), i.e. animations created in Adobe After Effects and exported to JSON via the Bodymovin plugin. These animations improve the user experience and can readily be incorporated into apps as if they were static images. Cobalt implements a “lottie-player” custom element with a playback API modeled after the Lottie Web Player (https://lottiefiles.com/web-player). In order to support Lottie, Cobalt updated its Skia port from m61 to m79.
Added support for MediaKeySystemMediaCapability.encryptionScheme.
Cobalt now supports
encryptionScheme can be ‘cenc’, ‘cbcs’, or ‘cbcs-1-9’. The default implementation assumes that:
It is possible to customize this behavior via an extension to
SbMediaCanPlayMimeAndKeySystem(). Please see the Starboard change log and the comment of
media.h for more details.
Added custom web APIs to query memory used by media source extensions.
cobalt/dom/memory_info.idl for details.
Added support for controlling shutdown behavior of graphics system.
Cobalt normally clears the framebuffer to opaque black on suspend or exit. This behavior can now be overridden by implementing the cobalt extension function
Added support for adjusting colors of 360 videos.
Platforms which support 360 videos may adjust the colors of the video frame using
Added support for rendering the frame with a custom root transform.
Platforms can force frame rendering to use a custom root transform by using
CobaltExtensionGraphicsApi::GetRenderRootTransform. This only impacts rendering; the web app does not know about the custom transform so may not layout elements appropriately.
Added support for UrlFetcher observer.
Platforms can implement UrlFetcher observer for performance tracing by implementing CobaltExtensionUrlFetcherObserverApi.
Added support for Cobalt Updater Notification.
Platforms can implement CobaltExtensionUpdaterNotificationApi to receive notifications from the Cobalt Evergreen Updater.
Improvements and Bugfixes
Support for QUIC and SPDY is now enabled.
QUIC and SPDY networking protocol support is added and these are enabled by default (if the server supports the protocol). This reduces roundtrip overhead and will improve networking overhead performance, especially on lower quality connections.
BoringSSL replaces OpenSSL enabling architecture-specific optimizations.
The update to BoringSSL brings with it the introduction of assembly-optimized architecture-specific optimizations that can bring a 5x speed up to cryptographic functions. This is especially useful when decrypting TLS for high-bandwidth video.
Added support for decoding JPEG images as multi-plane YUV.
JPEG images are decoded into RGBA in previous versions of Cobalt. The native format of most JPEG images is YV12, which takes only 3/8 of memory compare to RGBA. Now JPEG images are decoded into multi-plane YUV images on platforms with
rasterizer_type set to
direct-gles. As a result, when decoding to multi-plane image is enabled, image cache size set by AutoMem will be reduced by half due to the more compact nature of the YUV image format versus RGB. This feature can also be enabled/disabled explicitly by passing command line parameter
--allow_image_decoding_to_multi_plane to Cobalt with value
Improved image cache purge strategy.
Cobalt's image cache is now more aware of which images are likely to be reused (e.g. the ones referenced by HTMLImageElements, even if they are not currently displayed), and will now prioritize purging completely unreferenced images before weakly referenced images.
Added support for encoded image caching.
Cobalt now has support for caching the encoded image data fetched from the network. This enables Cobalt to keep the cached encoded image data resident so that when the user resumes, Cobalt does not need to do a network fetch for images again. The size of this cache can be adjusted via the gyp option
encoded_image_cache_size_in_bytes, or the command line switch
Added support for Device Authentication URL signing.
Cobalt will now add URL parameters signed with the device's secret key and certification scope to the initial URL. For more information, see doc/device_authentication.md.
Updated Chromium net and base libraries from m25 to m70.
Cobalt now has rebased its m25 net and base libraries to Chromium's m70 version of those libraries, bringing with it more functionality, better performance, and fewer bugs.
Media Codec Support.
Cobalt now supports the AV1 codec, the HEVC (H.265) codec, Dolby Digital (AC-3) and Dolby Digital Plus (Enhanced AC-3, or EAC-3).
Flexbox support added.
Cobalt now supports the Flexible Box Module, enabling web applications to take advantage of the more expressive layout model.
Support added for Chromium DevTools with V8.
Cobalt now supports the Chromium DevTools to help debug web applications. You can access it on non-gold builds by first starting Cobalt, and then using a browser to navigate to
http://YOUR_DEVICE_IP:9222. The Elements, Sources, Console and Performance panels are supported.
Support added for Intersection Observer Web API.
Cobalt now supports the Intersection Observer Web API to enable more performant checking of whether HTML elements are visible or not. Note that Cobalt's implementation currently does not support triggering visibility events that occur during CSS animation/transition playback.
Support for custom interface HTMLVideoElement.setMaxVideoCapabilities()
This allows the web application to express a guarantee to the platform's video player that a video will never exceed a maximum quality in a particular property. You could use this for example to indicate that a video will never adapt past a maximum resolution.
Platform Services API added
This API enables web applications to communicate directly to platform-specific services and systems, assuming the platform explicitly enables the given service.
EGL/GLES-based reference implementation of the Blitter API now available.
The Blitter API is now much easier to test locally on desktop computers or any device that already supports EGL/GLES. The new platform configuration is named
Add support for AbortController to the Fetch API.
The Fetch API is now updated to support the
Support added for HTMLAudioElement HTML tag.
This can be used to play audio-only media.
Add support for CSS3 Media Queries “dpi” value.
This can be used by the web application to adjust its layout depending on the physical size of the display device, if known.
Add support for scrollWidth, scrollHeight, scrollLeft, and scrollTop.
The web application can now query and set scroll properties of containers.
Initial support for Cobalt Evergreen automatic software updater added.
Cobalt is transitioning towards a runtime-linkable environment in order to support automatic software updates. Changes have been made around the Starboard interface in anticipation of this. Most notably, the EGL/GLES interface is no longer assumed to be available but rather Cobalt will now query the Starboard implementation for a structure of function pointers that implement the EGL/GLES APIs.
Part of this process involves moving options that were formerly build-time options to be instead run-time options. This will primarily be enabled by the new Starboard extensions framework. An example of an platform specific option added in this way can be found in cobalt/extension/graphics.h.
Cobalt code assumes that no errors are generated for unused parameters
There now exists Cobalt code where input parameters may be unused, and it is expected that toolchains will not generate errors in these cases. You may need to adjust your Starboard configuration so that your compiler no longer emits this error, e.g. build with the
-Wno-unused-parameter command line flag in GCC.
UNREFERENCED_PARAMETER has been removed, but
SB_UNREFERENCED_PARAMETER will continue to be supported.
MediaSession actions and action details have changed to match the spec
MediaSession now uses the newly specified
seekto action instead of the Cobalt 19
seek action, which has been removed. Also added
stop to the recognized actions, but the web app may not handle them yet. The
MediaSessionClient now uses a generated POD class for the IDL
MediaSessionActionDetails dictionary rather than an inner
Data class when invoking actions. (see: https://wicg.github.io/mediasession)
MediaSession supports setPositionState() function
MediaSession now supports the newly specified
MediaSessionClient now provides an immutable
MediaSessionState object that may be copied and queried on any thread to get a coherent view of attributes set by the the web app on the
Add support for size vs speed compiler flags
Performance-critical gyp targets now specify
optimize_target_for_speed: 1. For gold configs, these targets will use compiler flags
compiler_flags_gold_speed; other targets will use
compiler_flags_gold_size. For qa configs, the respective variables are
compiler_flags_qa_size. Only the qa and gold configs support these types of compiler flag gyp variables.
Improvements and Bug Fixes
--disable_media_codecs command line option to help with debugging.
--proxy command line flag in gold builds of Cobalt.
GetMaximumFrameIntervalInMilliseconds() platform Cobalt configuration setting (in cobalt/extension/graphics.h) to allow a platform to indicate a minimum framerate causing Cobalt to rerender the display even if nothing has changed after the specified interval.
v8, and additionally setting the gyp variable
cobalt_enable_jit to 1. These variables should be set from your
gyp_configuration.py Python file (and not for example your
Add support for animated WebP images with transparency
This was not originally supported by Cobalt, and any prior use of animated WebP with transparency would have resulted in visual artifacts.
Storage format changed from sqlite3 to protobuf
Cobalt's internal representation for persistent storage of cookies and local storage entries changed from sqlite3 to protobuf. The header of the SbStorageRecord blob was updated from SAV0 to SAV1 and all the data will be migrated to the new format the next time Cobalt is launched. The schema is available at cobalt/storage/store/storage.proto.
Cobalt is now configured to prefer an IPv4 address to IPv6 addresses when choosing an initial server address from DNS responses. That is, if a DNS response contains both IPv4 addresses and IPv6 addresses, Cobalt will now explicitly attempt to connect an IPv4 address before possibly moving onto IPv6 on connect failures. Unfortunately, we've discovered common scenarios where IPv6 addresses were listed in DNS responses but intervening network configurations prevented IPv6 use after connect time. This caused the previous implementation to appear as if no network was available.
Enable voice interactions
A subset of WebRTC APIs has been added.
getUserMedia can be used to get audio input stream from the microphone. The media stream can then be connected to
MediaRecorder to receive the audio data stored as
Blob objects which can later be sent over the network. This allows web apps to implement voice-enabled features without relying on the platform's capability to perform speech recognition.
Bison 3 required
Support for compiling with version 2.x of the GNU bison parser generator has been removed. Please update to version 3.x.
Improvements and Bug Fixes
@media rules would be assigned a CSS rule index relative to their position within the nested
@media rule rather than being assigned an index relative to their position within the parent CSS file. As a result, rules may have been assigned incorrect precedence during CSS rule matching.
Rebase libwebp to version 1.0.0
Update the version of libwebp used by Cobalt from 0.3.1 to 1.0.0. The new version brings with it performance improvements and bug fixes.
cobalt_enable_jit build variables
Move gyp variables
cobalt_enable_jit, which were previously defined in
starboard/build/platform_configuration.py, and can override it by providing a different one in their
GetVariables implementation. See the
linux-x64x11-mozjs platform for an override example.
IMPORTANT: While existing gyp files that define
cobalt_enable_jit may continue to work by chance, it is strongly preferred to move all declarations of these variables to python instead.
Move test data
Static test data is now copied to
content/data/test instead of
content/dir_source_root. Tests looking for the path to this data should use
BasePathKey::DIR_TEST_DATA instead of
BasePathKey::DIR_SOURCE_ROOT. Tests in Starboard can find the static data in the
test/ subdirectory of
Add support for cobalt_media_buffer_max_capacity
Allow bounding the max capacity allocated by decoder buffers, by setting the gypi variables
cobalt_media_buffer_max_capacity_4k. 1080p applies to all resolutions 1080p and below. Those values default to 0, which imposes no bounds. If non-zero, each capacity must be greater than or equal to the sum of the video budget and non video budget for that resolution (see
cobalt_media_buffer_non_video_budget, etc.), and the max capacities must be greater than or equal to the corresponding initial capacities:
Fix issue with CSS animations not working with the ‘outline’ property
There was a bug in previous versions that resulted in incorrect behavior when applying a CSS animation or CSS transition to the ‘outline’ property. This is fixed now.
Change default minimum frame time to 16.0ms instead of 16.4ms.
In case a platform can only wait on millisecond resolution, we would prefer that it wait 16ms instead of 17ms, so we round this down. Many platforms will pace themselves to 16.6ms regardless.
Make new rasterizer type “direct-gles” default
This is an optimized OpenGLES 2.0 rasterizer that provides a fast path for rendering most of the skia primitives that Cobalt uses. While it was available since Version 11, it is now polished and set as the default rasterizer.
Added support for the fetch and streams Web APIs
A subset of ReadableStream and Fetch Web APIs have been implemented. Fetch may be used to get progressive results via a ReadableStream, or the full result can be accessed as text, from the Response class.
HTMLMediaElement::loop is supported
Now the video plays in a loop if the loop attribute of the video element is set.
Add support for MediaDevices.enumerateDevices()
navigator.mediaDevices.enumerateDevices(). This returns a promise of an array of MediaDeviceInfo objects, each partially implemented to have valid
Improvements and Bug Fixes
Add support for document.hasFocus()
While support for firing blur and focus events was implemented, querying the current state via document.hasFocus() was not implemented until now.
Implemented Same Origin Policy and removed navigation whitelist
Add support for touchpad not associated with a pointer
This adds support for input of type kSbInputDeviceTypeTouchPad for touchpads not associated with a pointer.
Splash Screen Customization
The Cobalt splash screen is customizable. Documents may use a link element with attribute rel=“splashscreen” to reference the splash screen which will be cached if local cache is implemented on the platform. Additionally fallbacks may be specified via command line parameter or gypi variable. For more information, see doc/splash_screen.md.
C++11 is now used within Cobalt code, and so Cobalt must be compiled using C++11 toolchains.
Update SpiderMonkey from version 24 to 45; support ECMAScript 6
gyp_configuration.gypi file to set
Cobalt now supports the Fetch/Stream API.
On-device Speech-to-Text support
Support for utilizing the new Starboard speech recognizer interface in order to allow for on-device speech-to-text support is now added. The Starboard interface is defined in starboard/speech_recognizer.h.
Mouse pointer support
Cobalt now supports pointer events and will respond to Starboard
Custom Web Extension Support
window object visible to the web apps. This allows for custom web apps to interface with custom C++ code written outside of Cobalt common code. See doc/webapi_extension.md for more details.
Cobalt now supports adjusting the video playback rate.
AutoMem - Memory Configuration
AutoMem has been added which assists developers in tuning the memory settings of the Cobalt app. On startup, memory settings are now printed for all builds except gold. Memory settings can be altered via the command line, build files and in some instances the Starboard API. For more information, see cobalt/doc/memory_tuning.md.
Page Visibility API Support
Cobalt now supports the page visibility API, and will signal visibility and focus changes to the web app as the process transitions between Starboard lifecycle states. See the new Application Lifecycle Integration document for more details.
Added support for providing Opus audio-specific config to Starboard. Requires Starboard 6.
Linux build now supports 360 video
The Linux build linux-x64x11 now supports 360 video, and can be used as a reference implementation.
Stop the application if not retrying after a connection error
A positive response from
kSbSystemPlatformErrorTypeConnectionError now indicates that Cobalt should retry the failed request. Any other response now causes Cobalt to call
Frame rate counter
A frame rate counter is now made accessible. It actually displays frame times, the inverse of frame rate. In this case, 16.6ms corresponds to 60fps. It is accessible both as an overlay on the display by the command line option,
--fps_overlay. The data can also be printed to stdout with the command line option
--fps_stdout. The frame rate statistics will be updated each time an animation ends, or after 60 frames have been processed. Both command line flags are available in Gold builds.
Add support for rendering
kSbDecodeTargetFormat1PlaneUYVY (YUV 422)
Decode targets with the format
kSbDecodeTargetFormat1PlaneUYVY will now be rendered by Cobalt. This will allow decoders that produce YUV 422 UYVY video frames to now efficiently support 360 video.
Support for preloading an application with no graphics resources. See the new Application Lifecycle Integration guide for more details.
Improvements and Bug Fixes
display: none on an element.
offset_left and similar properties are no longer cause many expensive re-layouts to query.