SpaceX Landing Video Cleanup Making Progress

Maddog Batty (112434) writes 'The fine people at the NASA Space Flight Forum are making good progress on restoring the corrupted landing video reported earlier. It worth looking at the original video to see how bad it was and then at the latest restored video. It is now possible to see the legs being deployed, the sea coming closer and a big flame ball as the rocket plume hits the water. An impressive improvement so far and it is still being actively worked on so further refinements are likely.' Like Maddog Batty, I'd suggest watching the restored version first (note: the video is lower on the page), to see just what a big improvement's been made so far.

Re:Summary of techniques used?

[werepants]

I've been following the thread, but I don't know shit about video codecs or recovery so my understanding is limited at best. That said, it seems like FFMPEG (the codec used, I think) gains a lot of its compression by containing occasional keyframes that contain the full image, and then calculating deltas for providing subsequent frames. So, if you miss a few keyframes, you get huge swaths of video that are totally unintelligible. And, I think errors can cascade down into many subsequent frames because of the way the original image is modified and modified again.

As well, I get the impression that blocks within images can have the same sorts of issues, where an early bit or two in error can corrupt the entire thing. So, the effort has seemed to focus on trying to go through and fix keyframes first, and sometimes human pattern recognition can pick out the errors quickly, sometimes it looks like it has been a frame-by-frame trial and error where someone flips a bit and sees what comes out.

Given ~20 seconds of video, ~30 FPS, and probably several hundred blocks per frame, that's on the order of 100,000 pieces that are being repaired by human trial-and-error. It's a pretty herculean effort led by some extremely capable people.

Re:Summary of techniques used?

[dinfinity]

There's a wiki here: http://spacexlanding.wikispace... [wikispaces.com]

Re:Summary of techniques used?

[VideoPrincess]

Hi, I'm the user "Princess" on the NSF site and I've mainly been involved with cleaning up the file at the TS level. I can answer any questions you like. The best summary for the Slashdot audience would be this one [nasaspaceflight.com] by Lourens, it explains things simply without dumbing things down. The types of problems we have are basically that bits have been either flipped or (rarely) omitted. The flips tend to clump together, i.e. you'll get an area that's good and then an area that's awful. The work is approximately divided into two parts: fixing up the file, and fixing up the video that results. I work on fixing the file, and from that I can find extra frames and pieces of MPEG4 data for the video people. Fixing the video is done by using a modified version of ffmpeg that can change macroblock pointers, ordering, luma and chroma. This work is not done on the file directly and can't easily be mapped back to the file, so it's not just a question of flipping bits once you get to the video level. Other technical info: The video itself is a broadcast (fixed bandwidth) MPEG-TS stream containing one video stream, a 704x480 MPEG4 stream at approx. 15 fps (technically half the NTSC framerate which is 15000 / 1001 fps).

Re:Digital vs analog

[VideoPrincess]

Codec was MPEG4 in an MPEG-TS transport stream. The author of ffmpeg confirms it here [nasaspaceflight.com].

Re:Digital vs analog

[VideoPrincess]

No, codec was MPEG4 as explained [nasaspaceflight.com] by the author of ffmpeg!