Possible: BTIC1E (BPTC / BC6H / BC7 + Video Codec)
seeing as how my graphics hardware has a limited number of options for (non DXTn / S3TC) compressed texture formats, but does support BPTC / BC6H / BC7, which hinder effective real-time encoding (*), it may make sense to consider developing a video codec specifically for this.
*: though there is always the option of "just pick a block type and run with it", like always encoding BC7 in mode 5 or BC6H in mode 11 or something.
note: BPTC here will be used (in the OpenGL sense) to refer both to BC6H and BC7.
structurally, they are different formats, and need to be distinguished in-use.
when relevant, BC6H and BC7 (their DirectX names) will be used (mostly because names like "RGBA_BPTC_UNORM" kind of suck...).
essentially fairly similar to BTIC1C and BTIC1D (which in turn both derive from Apple Video / RPZA).
unlike 1C and 1D, it (mostly) sidesteps a lot of the complexities of these texture formats, and essentially treats the blocks mostly as raw data. this should still allow a moderately simple and fast decoder (into BPTC or similar).
also this stage of the process will be lossless.
this encoding allows a fairly arbitrary split between block-header and block data, which an encoder should be able to try to optimize for (and search for the "greatest savings" in terms of where to split up the block at). this also includes the ability to do "simple RLE runs" for repeating block-patterns, as well as to store raw/unencoded runs of blocks.
note that it isn't really viable to cleanly split between the header and index portions of a block given the way the blocks work.
RGB(A) Source Image -> Pixel Block Quantizer + BPTC Encoder -> BTIC1E Frame Encoder -> Deflate -> Packaging/Container.
Container/Packaging -> Inflate -> BTIC1E Decoder -> BPTC (passed to GL or similar).
the "Pixel Block Quantizer" step will basically try to fudge blocks to reduce the encoded image size; it is unclear exactly how it will tie in with the BPTC encoders. as-is, it is looking mostly like a tradeoff between an RGBA-space quantizer ("pre-cooking" the image) and a naive "slice and dice" quantizer (hack bits between blocks coming out of the BPTC encoder and see what it can get away with within the error threshold, basically by decoding the blocks to RGBA and comparing the results).
an issue: I have rather mixed feelings about BPTC.
namely, it is only available in newer desktop-class GPUs, and could be rendered less relevant if ETC2 becomes widespread in upcoming GPUs (both having been promoted to core in OpenGL).
some of this could potentially lead to cases of needing multiple redundant animated-texture videos, which would be kind of lame (and would waste disk space and similar), though potentially still better than wasting video memory by always using an RGBA16F or RGB9_E5 version.
could almost be a case of needing to implement it and determine whether or not it sucks...
figured the likelihood of BTIC1E sucking was just too high.
started working on another design:
which would be intended as a format to hopefully target both DXT and a BPTC subset, with other goals of being faster for getting to DXTn than BTIC2C, and compressing better than BTIC1C, target speed = 300 Mpix/sec for a single threaded decoder.
going and checking, the gap isn't quite as drastic as I had thought (if I can reduce the bitrate to 1/2 or 1/3 that of 1C, I will be doing pretty good, nevermind image quality for the moment).
I guess the reason many videos can fit 30 minutes in 200MB is mostly because of lower resolutions (640x360 has a lot fewer pixels than 1024x1024 or 2048x1024...).