Make Metadata-extractors fail fast

Use case description

Right now incorrectly videos with incorrect metadata failing to play with cryptic assert: Loading finished before preparation is completed

The most primitive scenario is to pass 0-length video. You could try it in any sample app.

Failure to find the moov segment by any reason causes the same assert. I guess failure to find tracks will cause the similar problem as well.

Proposed solution

The Extractor should throw an error instead of letting the upper layer to guess what went wrong. Ideally extractor should provide some information about file size, missing fields etc.

It will simplify debugging of such issues.

[ojw28]

It’s not feasible to implement such a feature in a sensible way. Codec support isn’t even evaluated in the MediaSource, since it’s not the MediaSources responsibility to try and play the media.

[ojw28]

Coming back to the original request:

I agree for the user there is no difference why video is not playing, but there is a difference for the application developer. And meaningful messages will definitely make the debugging loop shorter which will result in better user experience as the problems will be addressed faster. Isn’t it better to see an exception that video was 0 size instead of just Loading finished before preparation is completed?

Yes, it would definitely be better, but there are many thousands of potential reasons for failure in our extractors. It would not be a good use of time for us to create friendly debug messages for all of them, and it would add a significant amount of bloat to the library.

If it is impossible to narrow down why preparation has failed while loading of video was finished maybe it is possible to fast fail some well known cases?

The well known case is that the media is not malformed. I’m not sure that feeding a file of length 0 to the player is a common case. It’s also easy for a developer to debug themselves by taking a very cursory look at what they’ve fed in.

Maybe there is way to specify which extractor failed? Or tell which parameters are mandatory for an extractor?

Determining which extractor will be being used is equivalent to knowing what container format the media uses, which is also easy to determine with a very cursory look at what was fed in (e.g., mediainfo file.ext on the command line).