Kostya's Boring Codec World

Looks like the best way to collect a lot of samples is to become a developer and maintain demuxer/decoder. You may receive a lot of samples that do not decode with it 😉

I’d like to thank three major contributors (from Dania, Netherlands and Japan) of VC-1 in HD-DVD/Blu-Ray samples. It is because of them VC-1 video playback is less buggy than it was before (I know it still is but at least it’s improving).

This and last weekend I fixed some bugs in my decoder so now watching HD-DVD/BluRay movies will be a bit more pleasant ;-). But for the whole watching and listening experience you should wait for E-AC3 decoder (maybe it will be implemented during Google Summer of Code).

As for me, my systems neither are fast enough to decode it in realtime (1.42Ghz PPC G4 and PII 266Mhz) nor can even display full picture (max. resolution is 1280×1024 but I’m fine with it). So you may conclude I’m not interested in watching HD and you will be right. But I care for decoder and will fix bugs in it as I do already.

I’ve just added some support for WMV3 Complex Profile (aka old Advanced Profile).
I don’t know why most samples (users complaining about) I’ve met are anime. It’s a good chance they will work now.

And here is updated list of CP features explained:

• RES_X8 – additional bit at the end of I-frame header pointing if this is normal I-frame or this is special coded frame (I’m sure that’s exactly WMV2/8 J-frame with different header)
• RES_FASTTX – somehow interferes with P-frames but bitstream is not changed
• RES_RTM – old P-frame format (header should be the same but some additions on macroblock level). This is also quite common in old WMV3 files. Not RE’d yet

Now FFmpeg and MPlayer support VC-1 in MPEG2-TS streams which can be found on Blu-Ray discs.

Thanks to Martin for providing sample and Nico Sabbi for implementing handling of this in both FFmpeg and MPlayer.

For those whom it may interest.
What are the things needed to play HD-DVD movies in open-source multimedia player?

• Decrypted movie (use this tool)
• Demuxer support
• Video decoder
• Audio decoder

EVO demuxer is really just slightly modified MPEG stream demuxer. FFmpeg and MPlayer fresh SVN versions support it (MPlayer was there first). I don’t know about other multimedia players but that’s quite easy to implement.

Video decoding: there are three possible choices – MPEG-2, H.264 and VC-1. First two should work fine, the last one should work but with some bugs (I will fix them eventually).

Audio decoding: is also tricky – standard AC3 audio will work, DTS is supported via libdca and E-AC3 is still to be figured out.

Conclusion – try current SVN of MPlayer and see if it works to you. And if you care about Blu-Ray support (and it does not work) – please provide a sample.

See this picture?

I don’t know why it appears in quite a few VC-1 Advanced Profile official test samples (the rest I could decode are football trainings as in SP/MP samples).

Yesterday I’ve written VC-1 Elementary Stream demuxer and now have enough material to test interlaced decoding and other AP features (when I implement them).

And another task – make work VC-1 embedded in .EVO – official format of BlueRay/HD-DVD.

Known fourccs:

• WMV3
• WMVP
• WVP2
• WMVA
• WVC1

Known meaning of flags:

• RES_SM: really that’s two flags, RES_SM&2 indicated 411 interlaced mode and RES_SM&1 indicates sprite mode(or so it seems). These flags are mostly used by WMVP and WVP2
• RES_X8: I-frames may be packed with X8 algo. This also means that each I-frame has additional bit in frame header signalling if current frame should be encoded with X8 or with standard encoding scheme. Used in WMV3 Complex Profile.
• RES_FASTTX: still unknown, somehow interferes with motion compensation (at least it does not affect bitstream)
• RES_TRANSTAB: each macroblock should have its own DC/AC table index, not one global stored in the frame header.
• RES_RTM: Old version of WMV3 with different P-frame coding mode

X8 frames use their own Huffman codes (code lengths are stored as nibbles somewhere in bitstream) and also blocks looks like to be decoded in this way:

for(y=0;y

for(x=0;x< mb_width*2;x++){

decode luma block

if( x & y & 1)

decode both chroma blocks

}

}

Ever heard of codec with fourcc WMVP? That is another Windows Media variant designed for slideshows, video albums, ets. Why I have got interested in it? WMV3 Complex Profile (aka Ye Olde Undocumented and Incompatible Advanced Profile) uses exactly the same coding method to store I-frames when flag RES_X8 is set (if it is not set then VC-1 Main Profile decoder may decode that movies).

While standard decoder output mostly garbage, some blocks are decoded correctly thus I hope it’ll be possible to add support for both WMVP and WMV3 CP.