Forum : Technical Preview

Get all your questions answered about our latest Photosynth Technical Preview.


Topic: A question about encoding the video previews

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NateLawrence (10 months ago)
I grew up with the tail end of analog technology and the beginning of digital technology in terms of audio and video.

Two of the things that I really loved about analog media was being able to play things a variable speeds and also in reverse.

When we moved to digital video, compression was needed - at first for storage and later for transmission. With this compression we lost the ability to play back at variable speeds while retaining smoothness (due to the inability of hardware to decompress the information fast enough) and also lost the ability to play things in reverse (due to the compression methods used depending on the information seen in earlier frames being displayed first in order to show later frames).
NateLawrence (10 months ago)
With Photosynth 2's video previews you record movement through the synth both forward and backward and I assume that the forward and backward trips have many frames in common. 

My question for jafletch or anyone else involved is whether the video encoding you use tries to use any of the data from the first half of the video when writing the information for the reverse trip or whether this is all unique data.

I had always thought that by using standard compression methods in both directions we could still arrive at an output file which would still be significantly smaller than uncompressed but negligibly larger (perhaps even smaller?) than the one compressed to be decoded in forward playback alone.

It seems as though you could increase the quality of the video (or shrink the filesize if you maintain the same resolution) by using data from the forward trip when displaying the reverse trip (or vice versa) if you aren't already.
NateLawrence (10 months ago)
I'm also curious whether anyone out there has proposed standard controls for pieces of HTML 5 video or audio which have been encoded for bi-directional playback, as that seems more efficient for everyone involved in cases like your video preview.

I know that I can't be the only one who misses being able to scrub smoothly backward and forward in media.

I would love it if whoever is in charge of Microsoft's audio and video formats and players would keep open lines of communication with MSR's IVM, the Kinect team, your team, the IE teams for all supported platforms, and certainly the W3C and other browser vendors and media player vendors.

I'm not clear what sorts of advanced things h.625 is doing to shrink filesizes, but it seems to me that, at some point, capturing or generating geometry will dramatically shrink video filesizes by tracking an object's shape and pose throughout frames and only storing the changes in state, position, and illumination.
tapydisuza (5 months ago)
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