Custom URL loader

[Type1J]

Hello,

I have a desktop app with a webview.

The native app gives me access to video and audio segments, as well as information that I can use to construct a DASH manifest.

I think that using a base URL in the manifest with a custom scheme (i.e. my_custom_scheme://video/42.m4s) is what would make dash.js use some sort of plugin loader for the segments, and maybe the manifest as well.

The extensions to dash.js that I've seen have only modified a request that already has an XHR, etc., and I don't need an XHR since I'm not making a network request, just a call to the native app through functions that it provides to the web view. The other extension that I've seen is for indexed DB offline, and it looks much more involved than what I believe is needed: I just want dash to call a function that I make with an URL, and have that function return an ArrayBuffer/Uint8Array of the segment, and maybe headers, if that's needed by dash.js.

I'd also like to load the manifest with the custom scheme if possible.

I feel like there's already something in place that allows me to make such an plugin, but I haven't seen any documentation about it.

What do I need to do to make this plugin and register it with dash.js?

[bbert]

Yes there is something in place but I'm not sure if it is really possible to register a plugin from the application.
It is used inside dash.js by the OfflineController to enable segments fetching from local indexedDB storage, but don't know about other implementations.
Moreover the mechanism in place is not complete in my opinion since some points are missing such as a mechanism to enable the plugin to notify the dash.js core layer about the download progress.
@dsilhavy maybe we could add this functionnality in the scope of the 5.0 version?

[Type1J]

I saw the offline directory, but it has quite a few files, and I'm not sure where to start reading it. Does that mean that I will need to do something similar and compile a custom version of dash.js to make it work?

I don't think that progress is needed in my case, since segments are small, and ussually come in a few hundred nanoseconds.

[bbert]

I guess yes you'll have to compile a custom version.
Another way is to extend and override the XHRLoader class.
But I would definitely be in favor of having a scheme plugin mechanism as proposed by some other player.

[Type1J]

Thanks for your responses!

I guess I have to wait until @dsilhavy reponds to know if there's an expected way to use a custom loader. I'll look at the XHRLoader class in the meantime.

[dsilhavy]

At this point, I am not planning to implement support for custom loaders. There are issues with higher priorities at this point. If you can work on this, I am happy to review a pull request or a first architecture draft/idea.

[Type1J]

I'm not too familiar with the codebase at this point, but I need this functionality soon, even if I have to hack it together. Once I have it working, I'll try to make it more polished, and match the codebase style for a PR.

[dsilhavy]

Thanks this sounds good

[Type1J]

Hello again, I've made an extension to add my custom loader. The extension does not require recompiling the library, so it can be used from the npm published version.

I have run into an issue, though. My loader seems to start in a mid AdaptationSet, and then "adapts" to a lower one. I think that this is because I'm not reporting progress or some other stats. Can someone tell me what FetchLoader and HTTPLoader does to cause properly report? It seem quite complicated, and I think that I can probably do something simpler than what is there.

[Type1J]

I'm pretty happy that it's almost working! I think what I want to do is force a particular representation selection strategy, then provide timing data for how long my app's custom async fragment fetcher function takes. I'm not sure how to force a particular strategy, though. I think that most of this is the same between the published 4.x.x and 5.x.x (development) tag/branch, but I don't know how or what chooses the representation selection strategy. @bbert , @dsilhavy am I correct that I can set (force) a particular strategy? If so, how where is that set?

For some context:
I get settings by: const settings = dashjs.FactoryMaker.getSingletonInstance(context, 'Settings'); then, I get the representation strategy (I think) by const calculationMode = settings.get().streaming.abr.fetchThroughputCalculationMode;. I get the dashMetics and lowLatencyThroughputModel from the argument (config) passed to my loader (a function that returns an object with load and abort functions). My loader is selected based on the scheme of the URL. The load() function calls config.success() with either an ArrayBuffer for fragments or string for the manifest. Everything seems to be working fine except for the fact that after a few seconds, the lower bitrate representation is chosen. I'm basically using https://dash.akamaized.net/akamai/bbb_30fps/bbb_30fps.mpd with a <BaseURL/> to override the scheme and make my loader be used instead of the normal (HTTPLoader/XHRLoader/FetchLoader) loaders. Making the representation selection work is the only part that has given me difficulty.