ChannelMediaDecoder::Create(MediaDecoderInit& aInit, DecoderDoctorDiagnostics* aDiagnostics) receives a DecoderDoctorDiagnostics as a parameter, but we didn't use that at all, which is an useless parameter.

That was introduced in this, and at that time that parameter was already useless.

We should figure that either to make that parameter useful (hook that with the DecoderTraits::IsSupportedType()) or simply to remove that.

Thank you for looking into this.

(In reply to Alastor Wu [:alwu] from comment #0)

That was introduced in this, and at that time that parameter was already useless.

To be fair, "this" was bug 1409178 moving some code.
The real initial code was from bug 1248507, DecoderTraits::CreateDecoder() was passing DecoderDoctorDiagnostics to other functions, where it could be updated with diagnostic information. So it was not useless initially.

Anyway, regardless of this history, yes you'll need to decide if it's worth keeping this parameter now -- Could it ever be useful again in the future?

We should figure that either to make that parameter useful (hook that with the DecoderTraits::IsSupportedType()) or simply to remove that.

Right, I see DecoderTraits::CreateDecoder() is calling DecoderTraits::IsSupportedType (without DecoderDoctorDiagnostics), which interestingly is calling MP4Decoder::IsSupportedTypeWithoutDiagnostics! Maybe instead we could pass DecoderDoctorDiagnostics through to MP4Decoder::IsSupportedType?

Doing that allows us to accquire the error information from the DecoderDoctorDiagnostics.

https://hg.mozilla.org/mozilla-central/rev/4c2f16aad48f