Kostya's Boring Codec World

So, after a long series of delays and procrastination (the common story in NihAV development), I’ve finally stared to work on adding support for RMHD to my project. There are two things to be done actually: add support for RMHD container (so that I can demux actual files) and obviously support for RealVideo 6 itself.

As for RMHD container support, this was quite easy. Some person has given me a file about a year ago so I could look at it and improve my existing RealMedia demuxer. As expected the format is about the same but a bit different: magic word in the header now is “.RMP” instead of “.RMF”, some chunks were upgraded to version 2 (previously they all were either version 0 or version 1) with some additional fields shoved in the middle (or maybe they’ve upgraded them to 64-bit). The WTFiest change is how audio header was written: binary fields tell it’s header version 5 (it is) but text identifier says “.rm4” which obviously comes from version 4 and the provided header size is too short compared to the conventional RMVB and actual header data. At last after some hacks added to my RealMedia demuxer I was able to decode AAC track from the file so only the video part remains.

For RV6 I have the binary specification with a lot of debug symbols left. Even though I’ve made a good progress on it, I expect CEmpeg to add the opensource decoder for it first. After all, if you search for strings in the librv11dec.so from the official site you’ll see the function names that will make almost anybody recognizing them cringe:

C_hScale8To15(short*, int, unsigned char const*, short const*, short const*, int)
C_yuv2planeX(short const*, int, short const**, unsigned char*, int, unsigned char const*, int)
sws_pb_64
SSE2_yuv2planeX(short const*, int, short const**, unsigned char*, int, unsigned char const*, int)
SSE2_hScale8To15(short*, int, unsigned char const*, short const*, short const*, int)
yuv2planeX_8_c_opt(short const*, int, short const**, unsigned char*, int, unsigned char const*, int, int)

In case you belong to the blessed majority who do not know what those functions are, these are part of libswscale, a library for frame colourspace conversion and scaling licensed under LGPL. Which means pieces of it were borrowed and adapted for (YUV-only) frame scaling in RV6 decoder and thus it source code should be available under LGPL. And imperfect English messages in the same specification (“not support” consistently occurs throughout it) hint that it was quite probably Chinese developers responsible for this. Since CEmpeg has both the majority of libswscale developers and people who speak Chinese, it should be no problem for them to obtain the codes. Meanwhile I’ll continue my work because NIH in NihAV is there for a reason (that also reminds me I should port NAScale to Rust eventually).

Anyway, the actual description of RealVideo 6 deserves a separate post so I’ll dedicate the following post to it (but who would read that anyway?).

This entry was posted on Saturday, November 10th, 2018 at 9:22 am and is filed under NihAV, RealVideo. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.