Problem with playback speed using Gstreamer

[jimheath]

I've written a video player in C++ (Qt 4.8.4) which uses Gstreamer 0.10 and the Freescale aiurdemux plugin 3.0.7. It's running on Timesys' BSP for the Nitrogen6X board, Linux version 3.0.35-ts-armv7l. CPU: i.MX6Q, 1GB RAM. Videos are being played from an attached 1TB SATA 2.5" drive. The video format I'm using is MPEG-2 TS (transport stream) and encoded using H.264.

I'm trying to add fast-forward and rewind functions to the player and notice some strange intermittent behavior. When I increase the playback speed to 4 (fast-forward) or -4 (rewind), much of the time the player works fine. But sometimes I get the following error from Gstreamer:

GStreamer-CRITICAL **: gst_segment_set_seek: assertion `start <= stop' failed

This is happening when I'm trying to return to the normal playback speed of 1. I've checked my start and stop values and they are fine so I shouldn't be seeing this assertion error. When I get this error, the video continues at its current playback speed of 4 or -4. After repeated attempts of changing the playback speed, Gstreamer will eventually return to a rate of 1.

My code for changing playback speed is based on this Gstreamer tutorial: http://docs.gstreamer.com/display/GstSDK/Basic+tutorial+13%3A+Playback+speed

I've looked through the Gstreamer mailing list and someone mentioned this error is a bug but that was back in 2011. I would think it has been fixed by now...

Any ideas why this happens and how to fix it?

Thanks,

Jim

[LeonardoSandova]

Jim, can you do the same test using 3.0.9 or 3.0.10 version? On Yocto, the community dora brances are using gst-fsl-plugin_3.0.9 and master-next 3.0.10. Also, if you can duplicate the issue using just gplay, it would be great.

[jimheath]

Hi Leonardo,

I'll test it with gplay and report back. Where do I get Yocto for the Nitrogen6X board?

Thanks,

Jim

[EricNelson]

Hi Jim,

You can get a Dora release (w/3.0.9 gstreamer components) from here:

     http://boundarydevices.com/yocto-dora-release-mx6/

We don't have an image on-line with the 3.10.17 (3.0.10) versions.

You'd have to build with master-next, but kernel support is present.

[jimheath · Accepted solution]

Thanks Eric for the link to Yocto. I'll give that a try because it may solve our other open issue where Gstreamer fails to allocate enough contiguous memory to play a video: GStreamer crashing on i.MX6 (Boundary Devices Nitrogen6x)

Leonardo: That was a good idea having me try gplay; I didn't have the error when I used that program.

I looked at the source code to see how it was accomplished. It looks like the Gstreamer tutorial I referenced in my initial post has a mistake. Specifically this line:

seek_event = gst_event_new_seek (data->rate, GST_FORMAT_TIME, GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_ACCURATE, GST_SEEK_TYPE_SET, position, GST_SEEK_TYPE_NONE, 0);

here's the gplay version:

set_playback_rate_event = gst_event_new_seek(playback_rate, GST_FORMAT_TIME, GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_KEY_UNIT, GST_SEEK_TYPE_SET, current_position, GST_SEEK_TYPE_SET, pproperty->duration);

So I think the last two parameters are what was causing my problem. I used GST_SEEK_TYPE_NONE and zero. After changing it to GST_SEEK_TYPE_SET and the duration of the video, I no longer experienced the error.

Thanks again,

Jim