[Open-graphics] decoding video in real-time

[Vesa Solonen]

On Mon, 16 Apr 2007, Attila Kinali wrote:

> The issue of stream synchronus playback can be entirely
> solved in software and does not need to be done in hardware.
> Unless you need A-V sync below 0.5*frame-time, then you need
> at least a little bit information from the graphics card, when
> the current image drawing is finished, but any half decend card
> supports this.

The problem is _not_ A-V sync, but interference jitter between different 
frame rates. Please have alook at:

http://www.linuxtv.org/wiki/index.php/The_DVB_Decoder_Challenge#Screen.2FDecoder_Sync_Aliasing

If you imagine multiplying two square wave signals of different 
frequencies (like 50Hz for deinterlaced framerate and 60Hz refresh of the 
monitor...) and the resulting signal/spectrum. Then compare that to a case 
where both signals are of same frequency and in phase... Drawing some 
graphs on a piece of cross-ruled paper will help :) That will show the 
need for hw-capability of runtime adjusting of pixel clock around one 
permille. The means of adjusting may be quite rudimentary like flipping 
clock synthesizer dividers back and forth with adjustable duty cycle. 
Synthesizer response time needs to be set low enough so that it does 
averaging of the pulses.

-Vesa