Add ohos Backend with OpenHarmony Platform Specific API

[rayguo17]

Add ohos backend with OpenHarmony Platform Specific API

Justification

While Gstreamer is available across different platform with different build settings, it brings more overhead in loads, memory/storage usage to the device, and this is crucial for computing resource-constrainted embedded system like Phone and wearable.
Re-using the platform media pipeline will give Servo full performance boost on Open Harmony device.

Related Tasks

• Add Initial Stub for further development. initial stub for ohos backend #444

Dependencies

ohos-media-sys a.k.a player_framework

Documentation

Codec Kit
Media Kit

[ceyusa]

Out of curiosity I have some questions:

1. Does servo-media API match with oho-media?

2. What has your development experience been like?

3. Do you plan to set up a CI on GitHub?

While GStreamer is available across different platform with different build
settings, it brings more overhead in loads, memory/storage usage to the
device, and this is crucial for computing resource-constrainted embedded
system like Phone and wearable.

GStreamer has been successfully used in many products with resource-constrained
embedded devices. I recall TI's OMAP2, among other examples, leveraging
GStreamer due to its high degree of tailoring for specific needs.

That said, given that Servo's use case demands more than a minimal embedded
system, have you considered writing a GStreamer plugin to wrap oho-media instead
of writing a new backend?

[rayguo17]

In the past few months, I have been trying to use ohos-media-sys crate to implement servo-media API, specifically the Player trait in my local environment, and to some extend it is quite compatible. While i attemping to glue the System API and Servo-media, I am also exploring more in Gstreamer media stack, playing around with the existing gstreamer backend. The idea here is, in some scenario that only need limited media features we can choose to use a more direct API to avoid introducing unnessacery dependency. I am also open to writing a plugin to wrap ohos-media, as that also seems cool.