The following scenario works with 1.4 but not 1.6:

- make sure you don't have a H264 decoder installed (I do this by removing gst-libav from GST_PLUGIN_PATH).
- gst-launch-1.0 uridecodebin uri="rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mov" caps="video/x-h264,stream-format=avc;audio/mpeg" ! fakesink

I get this error with 1.6 but not with 1.4:

Missing element: H.264 decoder
WARNING: from element /GstPipeline:pipeline0/GstURIDecodeBin:uridecodebin0: No decoder available for type 'video/x-h264, stream-format=(string)byte-stream, alignment=(string)nal, parsed=(boolean)true'.
Additional debug info:
gsturidecodebin.c(939): unknown_type_cb (): /GstPipeline:pipeline0/GstURIDecodeBin:uridecodebin0


Backporting this patch fixes the issue:
https://cgit.freedesktop.org/gstreamer/gst-plugins-base/commit/?id=d50b713f44eb17ebf69aa771c26f8eb19e226319

1.6 logs: https://people.collabora.com/~cassidy/nodecoder-1.6.txt
1.6 + backported patch logs: https://people.collabora.com/~cassidy/nodecoder-back-1.6.txt

The difference is when gst_rtp_h264_depay_negotiate() calls gst_pad_get_allowed_caps() on its source pad.

With 1.6 the pad is not linked yet:
gstrtph264depay.c:183:gst_rtp_h264_depay_negotiate:<rtph264depay0> allowed caps: (NULL)
so h264parse use the default stream-format: bytestream.

While in 1.8 (and with the backported patch) it is linked:

gstrtph264depay.c:183:gst_rtp_h264_depay_negotiate:<rtph264depay0> allowed caps: video/x-h264, stream-format=(string)avc, alignment=(string)au; video/x-h264, stream-format=(string)byte-stream, alignment=(string){ nal, au }
so h264parse will use the right format.