Original commit message from CVS:
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_open),
(gst_ffmpegdec_negotiate), (clip_video_buffer),
(clip_audio_buffer), (gst_ffmpegdec_audio_frame),
(gst_ffmpegdec_frame), (gst_ffmpegdec_sink_event),
(gst_ffmpegdec_chain):
Mark outgoing buffers with DISCONT when needed.
Small cleanups.
Fix timestamps on audio decoders.
better audio clipping.
Fixes #352579.