The LZ4 Streaming Format specification has progressed quite a bit since last post, taking into consideration most issues raised by commenters. It has now reached version 1.4 (see edit below), which looks stable enough to start implementing the next version of LZ4.
As a consequence, save any last-minute important item raised by contributors, the currently published specification will be used in upcoming LZ4 releases.
[Edit] : and last-minute change there is. Following a suggestion by Takayuki Matsuoka, the header checksum is now slightly different, in an effort to become more friendly with read-only media, hopefully improving clarity in the process. Specification version is now raised to v1.3.
[Edit 2] : A first version of LZ4c, implementing the above specification, is available at Google Code.
[Edit 3] : Following recommendations from Mark Adler, version v1.4 re-introduce stream checksum. It's not correct to assume that block checksum makes stream checksum redundant : block checksum only validates that each block has no error, while stream checksum verify that all blocks are present and in correct order. Finally, stream checksum also validates the encoding/decoding stage itself.
v1.4 also introduces the definition of "skippable chunks", which can encapsulate user-defined data of any kind, and be integrated into a flow of LZ4 streams.