[pvrusb2] Best MPEG2 Stream Editor for Hauppauge Created MPEG2 Files

Tue Dec 25 00:51:49 CST 2012

Roger:

When you're using an HVR-1950 - actually *ANY* tuner to perform ATSC 
capture - you're not really "capturing" anything in the traditional 
sense.  Unlike old analog video where the broadcast format uses 
"pre-digital age" separately modulated analog video and audio, when 
you're grabbing ATSC all you are doing is grabbing a bit stream from the 
broadcast station.  Nothing more.  The "tuner" in this case is very very 
simple - all it has to do is demodulate the station's carrier to recover 
the bit stream.  The tuner actually doesn't have to care at all what is 
inside that bit stream - that's "somebody else's problem...".  All 
timing information is part of that bit stream, and audio vs video data 
within it is just subpackets in the container format.  In fact, ATSC 
data is really just MPEG container format with just some additional 
rules applied.

The HVR-1950 tuner when run in ATSC mode just grabs the bits and all the 
pvrusb2 driver does is hand the bits off to the DVB core (which then 
does further processing on the bit stream to select out specific 
subchannel data packets from the overall data flow).  So if you have 
issues of audio / video sync, or problems with frame synchronization, it 
really can't be caused by the tuner or the driver.  In fact the only 
possible scenario here is if the received signal is too weak then the 
demodulated bit stream could have dropouts / corruption in it - but that 
would be true for any tuner setup.

The previous audio / video sync issues you are refering to from a long 
time ago would have had to do with analog capture, which is completely 
different.  In that case, the hardware is quite a bit more complicated, 
since it has to separately recover the video & audio signals, render the 
video into frames and then encode all of it merged to mpeg for delivery 
to the application.  None of those steps happen with ATSC since the 
transport data received is already mpeg data.

ATSC video tuners are actually simpler than analog tuners.

Happy holidays,

  -Mike

On Mon, 24 Dec 2012, Roger wrote:

> 
> >> Think I'm running into an issue with streams created by the pvrusb2
> >> driver, or
> >> Hauppauge devices.
> >>
> >> Avidemux seems to loose sync, even after manually specifying NTSC (~29
> >> fps).
> >> On initial import of the video, the FPS is set to an initial >50 fps.
> >>
> >> I've tried everything within avidemux, and it just doesn't seem to even
> >> play
> >> the Hauppauge streams with a correct audio:video sync, although changing to
> >> 29-30 fps really helps.
> >>
> >> Just want to shrink some large TV broadcasted MPEG2 streams.  Cutting
> >> commercials seems to reduce the file from 8GB to 4GB.  I'm seriously just
> >> thinking of burning them to a Blu-Ray disk, but that's quite expensive.
> >> (Thinking the later might be more feasible at this point.)
> 
> > On Mon, Dec 24, 2012 at 09:19:25PM +0100, Emmanuel Touzery wrote:
> >Are you using avidemux 2.6?
> >For av in 2.5 and 2.6 work equally well for me but for tv enission
> >recording (dvb-t in europe), only 2.6 works well for audio sync.
> 
> I'm in the US using (DVB) ATSC.
> 
> The same video, plays just fine with mplayer.  Never had a problem with 
> audio/video sync.  I used to capture video using mencoder, but then ran into 
> audio/video sync issues and resorted to dd.
> 
> I'm using avidemux-2.5.6, while avidemux-2.6* series is hard masked here on 
> gentoo.
> 
> I have tried playing around with exporting with different settings with no 
> success.
> 
> I've also just tried cinelerra-20120707, and the audio is drifting far off too 
> on playback.
> 
> 
> This is TV Broadcasted video grabbed from an hvr-1950 using dd from the 
> /dev/dvb device.  Not using mplayer/mencoder for recording as it further 
> processes the video before saving.
> 
> I was using cat prior to using dd, but cat had issues with large files or 
> reception quality (unusual chars) or something.  dd has proven more reliable.
> 
> So, I'm using the raw original stream.
> 
> Some things from past notes, it's been stated extra frames could be being 
> broadcasted to ensure quality, hence the reason for 59.940 fps when playing 
> with mplayer.  Mplayer also starts complaining every few frames about switching 
> framerate/fps.  I'm I'm thinking the later might more likely be the reason.
> 
> ---Begin of Mplayer Snip---
> demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
> A:34534.1 V:34535.7 A-V: -1.629 ct: -0.050  51/ 33 19% 26%  0.3% 3 0
> 
> demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
> A:34534.1 V:34535.7 A-V: -1.621 ct: -0.052  52/ 34 18% 27%  0.2% 3 0
> Warning! FPS changed 47.952 -> 59.940  (-11.988010) [7]
> A:34535.2 V:34536.8 A-V: -1.641 ct: -0.113 114/ 70 11% 16%  0.2% 3 0
> 
> demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
> A:34535.4 V:34537.0 A-V: -1.586 ct: -0.133 124/ 80 10% 15%  0.2% 3 0
> 
> demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
> A:34535.4 V:34537.0 A-V: -1.598 ct: -0.135 125/ 81 10% 15%  0.2% 3 0
> Warning! FPS changed 47.952 -> 59.940  (-11.988010) [7]
> A:34538.4 V:34539.9 A-V: -1.503 ct: -0.256 300/153  9%  8%  0.2% 3 0
> ---End of Mplayer Snip---
> 
> 
> The Hauppauge audio/video sync was such a popular problem on the message boards 
> without any resolution, and the only thing that comes to my mind is it may have 
> been fixed with a firmware update, or a unique work-araound applied quietly 
> within mplayer.
> 
> Well, one things certain, I'm sure I'm on the right mailing list -- as if 
> anybody knows, it would be people here!  And, as I said, not going to pull my 
> hair out on this.  I usually just watch things once and discard the recorded 
> show anyways.  Likely the issue is only with TV broadcasted material and not 
> with composite input recording.
> 
> --
> Roger
> http://rogerx.freeshell.org/
> _______________________________________________
> pvrusb2 mailing list
> pvrusb2 at isely.net
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> 

-- 

Mike Isely
isely @ isely (dot) net
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