On Tue, Jan 22, 2002 at 04:04:40PM +0000, Stephen Davies wrote: > Hi, Hi Stephen, > I hope that this doesn't go too far off topic for the list. That would be difficult considering the wide range of dicussion here. :-) I like it though. > I have a Linux machine that I use for video functions at home. > This machine outputs video to PAL TV using a Voodoo3 card (with bt869 TV > encoder) and XFree. I mostly play video files using mplayer's XV driver. I use a Radeon on NTSC. > So - my output display is interlaced. I guess mine is too. > A niggly problem for me has been that mplayer's playback does not lock > frame playback to the video card refresh - so playback suffers from a > "tear" What is a "tear"? Is that the effect where you see part of one frame and part of another at the same time, most noticible with panning motions? > when mplayer changes frames whilst the TV is scanning a visible > part of the screen. Also, playback is juddery - especially noticable on > pans and scrolls - caused by inconsistent display time for each video > frame. What is judder, exactly? > These effects are irritating but not a showstopper for me. I have always > used mpeg1 capture at 352x288 resolution I use mpeg1 to but at 320x240 due to my standard being NTSC over here. I do want to jump to 640x480 using mp1e (FFMPEGrec cannot capture 640x480 on my Athlon TB 800, mp1e does it at less than 50% CPU!) but it is still causing me problems. The latest is mp1e locking up and not writing the file anyomre. There is a fix checked in that I have to test still though. > But I've now added a DVB-T card to my setup. This captures over-the-air > transmitted MPEG2 streams. This video is often true interlaced video. OK. I have been thinking about DVB. From what I understand and you seem to be confirming... that what you actually receive from the broadcast source is an MPEG2 compressed stream. This is sweet. Way nicer than having to receive uncompressed and then compress one's self. So DVB is the "digital" interoperable standard which broadcasters and receivers can transfer MPEG2 streams right? So if one's provider is DVB compliant, one can go out and buy any old DVB compliant "cable converter" and not have to buy the one the provider rents or sells you. Remember the days when you had to go out and buy an analog cable converter because cable companies were adding lots of channels beyond the 13 that your old television got? But then TVs started to be produced that could tune beyond the 13 channels of older televisions so you could get rid of the cable converter. Would I be correct in parallelizing that situation to the status of DVB right now? Soon(ish) televisions (and other devices, like capture cards, one of which you seem to have now) will be created following the DVB standard and therefore will work on any DVB compliant provider? It sure seems like the right way to go. Get the compressed stream from the source and save it as you get it instread of everybody from source to destination doing their own compression and decompression. How big is an hour of DVB MPEG2? > Playback of these streams on my system give rather horrible results. On > top of the general problems above, oftentimes the lack of sync between the > TV and mplayer's displayed frames results in the video fields appearing > out of order - top field of frame 2 being displayed followed by bottom > field of frame 1. This shows the two fields out of time order. Result - > horrible flicker in moving areas. I can see how this would be a problem. > To fix this properly I need to get mplayer's frame playback locked to the > frame VSYNC of the video card. (Or, perhaps, lock the video card to > mplayer's frame playback?). I believe that with this done, a Linux box > could give video playback indistinguishable from broadcast. Now that would be really nice! This whole topic of VSYNC access sounds very much similar to what another user (Billy Biggs) is trying to accomplish. Maybe the archives could be useful. > Seeing we now have servicable video capture and playback on Linux, now > seems the time to make it really good quality! Amen! > What are my options? Are there any facilities in Xv/X to sense display > card vsync? Have I missed the obvious fix for this? That I don't know but I am really interested in what you find out or even better what you can do with Mplayer to make the quality even better by syncing its frame display to the VSYNC on the video card. Keep us posted please. b. -- Brian J. Murrell
