Documentation for L4T 19.3 is now available at the Linux For Tegra R19 support page: https://developer.nvidia.com/linux-tegra-rel-19.
It includes guides that should help with many of the issues raised in discussion on these forums. The documents include:
- Linux Driver Package Developers' Guide - Includes help on U-Boot and creation of a cross-compiling toolchain.
- Jetson TK1/Tegra Linux Driver Package Multimedia User Guide - Information on usage of Gstreamer for video compression/decompression, capture, playback, and conversion.
- Software Feature List - Describes software as well as multimedia codecs included in L4T.