Original commit message from CVS:
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_open),
(gst_ffmpegdec_setcaps), (gst_ffmpegdec_negotiate),
(get_output_buffer), (gst_ffmpegdec_video_frame),
(clip_audio_buffer), (gst_ffmpegdec_audio_frame),
(gst_ffmpegdec_frame), (gst_ffmpegdec_chain),
(gst_ffmpegdec_register):
Use caps to clip output images. Fixes #341736