id	summary	reporter	owner	description	type	status	priority	milestone	component	resolution	keywords	cc	parents
5445	Certain media hang on generating thumbnail	ayleph		"A user is uploading a number of ogg video files to my instance (videos with .ogg extension). These files transcode fine, which makes me think I have the correct python bindings for ogg files, but they hang at the thumbnail stage. Once this happens, that celery worker becomes stuck waiting and cannot be used for anything else. When enough of these files get uploaded and processed, all of my celery workers become stuck and nothing else proceeds. I have to restart my celery service to kill the stuck workers and make them available for use again.

I added a bunch of debug logging statements and tracked it down to the following line in `mediagoblin/media_types/video/transcoders.py`.

{{{
sample = appsink.emit(""pull-preroll"")
}}}

Online gst documentation says that `pull-preroll` may block until the preroll buffer or EOS signal is received, which appears to be happening on my instance with these video files.

> The normal way of retrieving samples from appsink is by using
> the gst_app_sink_pull_sample() and gst_app_sink_pull_preroll() 
> methods. These methods block until a sample becomes available 
> in the sink or when the sink is shut down or reaches EOS.
>
> If a blocking behaviour is not desirable, setting the 
> ""emit-signals"" property to TRUE will make appsink emit the 
> ""new-sample"" and ""new-preroll"" signals when a sample can be 
> pulled without blocking.
>
> The ""caps"" property on appsink can be used to control the 
> formats that appsink can receive. This property can contain 
> non-fixed caps, the format of the pulled samples can be 
> obtained by getting the sample caps.
>
> If one of the pull-preroll or pull-sample methods return NULL, 
> the appsink is stopped or in the EOS state. You can check for 
> the EOS state with the ""eos"" property or with the 
> gst_app_sink_is_eos() method.

https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-base-libs/html/gst-plugins-base-libs-appsink.html"	defect	closed	major		programming	invalid	gstrreamer,video,thumbnail,ogg	Boris Bobrov