Kostya's Boring Codec World

So while russia demonstrates once again what a hysterical führer and his similarly minded generals would do, I’m trying to do something to distract myself from the thoughts about the losses Ukraine suffered in last couple of days (and previous couple hundreds of days too).

Accidentally I’ve managed to find a sample in IVF format—the original streaming format for Indeo codecs. Despite the expectations it was not a renamed AVI file which made it even more interesting. So I took Ghidra and binary specification and started implementing it.

The format by itself is rather simple and the only interesting thing is that it transmits video data in passes: first it’s just bare minimum keyframes and all other frames as drop frames, then some inter frames are sent, then more data is sent and more. Unfortunately there’s no obvious field to tell where each part starts so I simply assemble frames in memory (which is not effective but still better than the original creating temporary files for assembling fragments).

Then there was a problem with decoding them: my existing decoder expected a frame with sequential structure while in this case fragments are transmitted out of order. Normally you’d get all four bands for luma plane and then a band for each chroma planes but in this case it may be one or two bands for luma plane, then chroma plane bands, then some zero padding and then the rest of the bands for luma (if they were transmitted at all). In the reference implementation the demuxer seems to parse and re-assemble the frame while I ended up writing a slightly different decoder for this scalable mode. It seems to work fine so now NihAV support for Indeo family of formats is even more complete than ever.

P.S. The Wiki had only the entry for Duck test samples format (that has the same extension) so somebody had to correct that. Which also makes me think about things like Duck AVC, AVS being an FMV game format or Chinese non-Duck AVC rip-off, IEEE AAC and so on. This confusion deserves to be written about but don’t expect me to do that.

This entry was posted on Thursday, October 13th, 2022 at 1:16 pm and is filed under Various Video Codecs. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.