High level Description: I have an issue with an application that works with Gstreamer 1.8.x but has stopped working correctly in 1.12.x.  I have tested this under Ubuntu 16.04 and 17.10. The issue is related to the gapless playback of video clips.  With GStreamer 1.8.x the application works fine.  With 1.12.x, clips fail to play and/or partially play (freezes).


Overview: I have a Python based application that plays back MP4 video files.  These are H.264 encoded files.  I have the 'about-to-finish' event handler set the filepath of the next video file via the URI property.  This works just fine with GStreamer 1.8.  However, due to needing 1.12 for other aspects of my project, we are moving to 1.12. We have confirmed the issue on multiple machines with Ubuntu 16.04 and also under Ubuntu 17.10. 

Steps to Reproduce: I have produced the following file:

http://www.pitchpipetuner.com/playbin-bug-example.tar.gz (size: 68.1M, MD5: 2262bd3d5e2b008972b74adfabfd9913) 

which contains the following 5 files:
5db561c2de3a39fa66a695146e925330  playbin-bug-example.py
5717031aa9ff8e1b5ac11fe1be91312b  test001.mp4
9ff97ee924314eeafe116861211a1b61  test002.mp4
8d020998d7430f7c8fc895392f46531a  test003.mp4
98081e5bd7b3c1b2d17448821dd7245f  test004.mp4

Under Ubuntu 16.04 with GStreamer 1.8 installed this works as expected and all 4 files playback fine.  Under Ubuntu 16.04 with Gstreamer 1.12 installed, the first clip will play, the second will not, the third will play for a few seconds in the middle of it's duration, and the forth will start to play.  We've seen the same exact playback errors on 3 machines.

Additional Info: The video files are come as raw H264 from a Raspberry Pi + camera, and then are 'wrapped' via MP4Box into MP4 files.