[mythtv] [mythtv-users] Sound a second behind video

[Mark Hutchinson]

On 13-Mar-08, at 8:44 AM, Yeechang Lee wrote:

> [Crossposted to mythtv-dev; please trim as appropriate when replying.]
>
> Michael T. Dean <mtdean at thirdcontact.com> says:
>> So, since you and others have found that ffplay doesn't work well
>> (and I just verified--in ffplay sound played almost a second before
>> the video in the commercials, but was in sync during the show),
>
> I've seen the issue Mark describes, or something like it, since first
> building my MythTV box more than two years ago. I only have digital
> MPEG-2 sources via FireWire and OTA. Unlike Mark, however, I don't
> recall seeing it in SD over FireWire (certainly not in analog-channel
> cable recordings; I still haven't watched enough from digital cable
> channels to be able to say one way or another). What I *have* seen is
> what I described at <URL:http://svn.mythtv.org/trac/ticket/1940> in
> June 2006. Contrary to what I wrote there, I have since seen the issue
> in pillar- or letterboxed SD commercials in the middle of HD
> recordings. I never pursued it further because with commflagging I
> just never see enough commercials for it to matter to me.
>
> I suspect the issue is tied in some way to the (very) longstanding
> issue at <URL:http://svn.mythtv.org/trac/ticket/799>. Below I list the
> various recording types (all MPEG-2 over FireWire and OTA, again) I've
> seen:
>
> 1 Elapsed time according to the internal player equals actual
>  recording time. All 720p recordings from ABC and FOX and all/most
>  1080i recordings from CBS, The CW, HDNet, and HDNet Movies fit in
>  this category. From these sources, all recordings have 29.97 frames
>  per second. No playback issues whatsoever.
> 2 Elapsed time equals about 80% of recorded time. All 1080i recordings
>  from the premium-movie channels (HBO, Showtime, etc.) are like this;
>  so are recordings from many SD channels. Many comments for #799 from
>  me and others describe this issue. Playback is fine, except
>  occasionally (perhaps a few times per movie) the video will "speed
>  up" for a second or two. Audio does not seem to be obviously
>  affected. Skipping back more than a few seconds and playing through
>  the portion again will generally (not always) reproduce the problem.
> 3 Elapsed time equals about 86% of recorded time (e.g., 52-53 minutes
>  for a 60-minute recording). Most NBC recordings fit into this
>  category. Discussed at
>  <URL:http://www.gossamer-threads.com/lists/mythtv/users/ 
> 227272#227272>.
>  Similar playback issues as with 2. Also, audio/video sync issues
>  during many non-HD commercial breaks. I'm pretty sure it's the same
>  problem as . . .
> 4 Elapsed time is about 30 seconds to two or three minutes below
>  recorded time. Most NGC and Discovery HD, and many PBS recordings,
>  fit here. I suspect the only difference between this and 4 is that
>  NBC airs a lot more commercials.
> 5 Like 4, but applies to Leno or Conan on NBC. The issue here seems
>  reversed; the program itself has proper 29.97fps frames, but
>  commercials and other non-HD segments (like a clip from a movie a
>  guest is promoting) may not. Audio/video often gets desynced during
>  such portions, and the desync will continue when the HD portion
>  resumes; pausing/unpausing or skipping around will cure the problem.
> 6 Elapsed time is about 66-68% of recorded time (e.g., 41-42 minutes
>  per hour recording). The newest variant, which I've seen on two
>  recent NGC recordings. Playback is fine, but the issue I note for 2
>  happens slightly more frequently (still not frequently enough to be
>  a serious problem), and audio during these bursts does also get
>  speed up, before both return to normal a second or two later.
>
> Note that rebuilding the seektable via 'mythtranscode -k -b' does
> nothing to change the situation in any of the above cases. Could the
> issues in 2 through 5, as well as #799 in general, be solved--albeit
> in a ham-handed way--by ignoring the built-in frame data entirely, and
> if necessary generate a new seektable that goes by actual recording
> time only?
>
> -- 
> Frontend:		P4 3.0GHz, 1.5TB software RAID 5 array
> Backend:		Quad-core Xeon 1.6GHz, 6.6TB sw RAID 6
> Video inputs:		Four high-definition over FireWire/OTA
> Accessories:		47" 1080p LCD, 5.1 digital, and MX-600
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Ticket 4940 opened for this.  Lots of information and sample within  
for the devs.