Hello, a question for the flash hackers here:
The project I’m doing requires dynamic variable FLV playback speed adjustment. The user is de facto running on a threadmill with a sensor. The faster the user runs the faster the video displayed on the monitor plays. A similar desktop-based tech was done here: http://outsideinteractive.net/software.php
I realize this problem is generally regarded as impossible using traditional methods but I’m willing to go the extra mile and try experimental technologies. Here’s what I’ve come up so far:
[SIZE=4][FONT=century gothic]1) Interpolation-based seeking[/FONT][/SIZE]
seek to the nearest frame that corresponds to where the video should be and stop, repeat every frame.
CONS: choppy as hell, buffer may/will go FUBAR
PROS: simple and allows for fully dynamic variable playback
[SIZE=4][FONT=century gothic]2) Software frame buffer[/FONT][/SIZE]
Render video to bitmaps and store the bitmaps in a buffer, display and then discard them according to the frame rate.
PROS: video display has potential to be smooth if the buffer can be rendered on time
CONS: garbage collector will have a field day - a single frame of 720p is 3,5mB, 48 frames are 170mB. In addition the CPU load may set the machine on fire or something.
[FONT=century gothic][SIZE=4]3) Multithreaded frame buffer using worker threads[/SIZE][/FONT]
Basically option 2, just that the rendering isn’t done in the main thread but in separate workers. Reserves 1 to 3 cores to rendering the video to bitmap and pushing it to the software frame buffer.
PROS: theoretically faster playback as up to 3 cores can be used to render the frames
**CONS: **I have no idea how efficient sending data between threads is but the worst case scenario is 85mB/second. The runtime may curl up and die.
[SIZE=4][FONT=century gothic]
4) Serverside time disortion and streaming[/FONT][/SIZE]
The client just passively displays a live stream, the server does the actual work by adjusting the video stream realtime. A server like FMS or RED5 will be used.
PROS: Will work on any machine, anywhere, easy to implement client-side
CONS: Required dedicated server (and a VERY beefy one at that), doesn’t use client-side number crunching power (which is free)
[SIZE=4][FONT=century gothic]5) Native browser plugin[/FONT][/SIZE]
Simply enough develop my own plugin, much like the DivX video player, VLC plugin or PDF reader… or flash itself!
PROS: native code performance, will run on any machine
CONS: different browsers, different operating systems - too close to the silicon for comfort. And building a cross-platform UI in C is a ɥɔʇıq. In addition that seems to be too much complexity for the project - there has to be a simpler way.
[SIZE=4][FONT=century gothic]6) Several speed-adjusted videos (courtesy of bwhiting)
[/FONT][/SIZE]Create a series of videos with different actual speeds - let’s say 1.4, 1.8, 2.2, 2.6, 3.0 - that’s 5 videos for speeds from 1 to 3. Then play the correct video depending on which speed is required
PROS: the simplest solution, elegant, only one video playing, low resource usage
CONS: requires a fiber-optic connection, streaming 5 HD videos at the same time will kill the memory and the bandwidth. Switching in-between may be choppy and there’s little granularity in speed. When the desired speed oscillates at the border levels the videos will constantly switch.
[SIZE=4][FONT=century gothic]7) Dynamic RAW video re-encoding* (courtesy of cleong)*
[/FONT][/SIZE]Decode the video, speed it up and encode it back into a RAW format, then stream that RAW bytearray to the player - do the computing in a separate thread and use alchemy for speed.
PROS: potentially the fastest and best solution - the Video object is the best for displaying Videos and the only performance hit is during the re-encoding.
CONS: I have absolutely no idea how to speed-up and reencode the video in a FAST way. Do you?
What do you think about those approaches? Which is the best? What would YOU do? Maybe you have a different approach?
Any thoughts, ideas, tips, lolcat images, links, code samples or whatever input is appreciated and welcome.
