[mythtv-users] Playback Video Stutters & Audio Quits on one Frontend

[John Pilkington]

On 10/08/2020 02:01, Tim Pletcher wrote:
> 
> 
> On Sun, Aug 9, 2020 at 5:47 PM Craig Huff <huffcslists at gmail.com 
> <mailto:huffcslists at gmail.com>> wrote:
> 
>     On Wed, Aug 5, 2020 at 9:05 PM jam <jam at tigger.ws
>     <mailto:jam at tigger.ws>> wrote:
> 
> 
> 
>          > On 5 Aug 2020, at 8:09 am, Craig Huff <huffcslists at gmail.com
>         <mailto:huffcslists at gmail.com>> wrote:
>          >
>          > I'm stumped and need help.  I've been trying to understand
>         why some video files work fine and others give me grief.  If I
>         play a "bad" file on my BE/FE, it plays just fine.  If I play
>         the same file on the remote FE, it will play ok for a second or
>         two, but then the audio quits and the video will stutter like
>         it's in slow motion.  If I play a "good" file, it works just
>         fine anywhere.
>          >
>          > A "bad" file is one of my older recordings that has a file
>         type description of:
>          >           "MPEG sequence, v2, program multiplex"
>          > (using the 'file' command in an xterm).
>          > A "good" file is one of the newer ones with a description of:
>          >           "MPEG transport stream data".
>          >
>          > The BE/FE is based on an ASRock Z77 Extreme4 motherboard with
>         an Intel Core i3-3250 CPU @ 3.50GHz, integrated HD Graphics 2500
>         and 16GB of RAM.  The video connection is DVI-D.
>          >
>          > The remote FE is based on an ASRock A785GM-LE motherboard
>         with an AMD Phenom II X4 965 CPU @3.4GHz, Nvidia GT710 PCI-E 2.0
>         Graphics adapter, and 4GB of RAM.  The video connection is HDMI
>         (with 5.1 Audio via the HDMI cable).
>          >
>          > The ethernet connection is 1GB/second rated, not tested.
>          >
>          > I fiddled around with various audio options and the
>         pre-defined VDPAU profiles (made things worse! -- audio would
>         drop out faster) vs. the High Quality profile.  I tried tweaking
>         processor settings with cpufrequtils and only managed to get it
>         running so hot it would freeze up until I forced it to shutdown
>         and waited for it to cool off again.
>          >
>          > Short of transcoding the problem files to a format that
>         works, or getting completely new hardware for the remote FE, I'd
>         appreciate any suggestions for what I might have missed to try
>         and get this to work.
>          >
>          > I'd also appreciate any advice on how to transcode the files
>         into a format that will not cause this problem, preferably using
>         Handbrake, Avidemux, and/or ffmpeg.
> 
>         I’d be very interested too!
>         One of my FE is a wireless laptop. Most movies play just fine
>         (including HD), but every now and then is a movie that is always
>         stuttery
> 
>         James
> 
> 
>     Sadly, rebuilding seek tables didn't change anything.  I believe the
>     problem is with SD recordings captured using PVR-500 tuners that I'm
>     trying to play back on an HD TV via HDMI on a remote FE.  They play
>     successfully on the BE/FE connected to a digital monitor via DVI. 
>     ffprobe describes the couple I'm focusing on as:
>              Video: mpeg2video (Main), yuv420p(tv, top first), 720x480
>     [SAR 8:9 DAR 4:3], 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
>              Audio: mp2, 48000 Hz, stereo, s16p, 384 kb/s
> 
>     I will try to see what I can come up with to transcode them to MP4
>     or h.264 and see if that helps.  Any suggestions from the peanut
>     gallery gratefully appreciated.
> 
> 
> 
> Just a guess, but perhaps the presentation timestamps in these older 
> recordings are messed up.  The audio / video synchronization approach in 
> v31 was changed to rely on these values from the recording file and 
> perhaps some decoders are more tolerant than others??
> 
> You might look into regenerating timestamps with ffmpeg.  I haven't 
> tried any of this myself as I don't have old recordings with this issue 
> but some of the discussion in this thread might provide some options:
> https://superuser.com/questions/1159056/ffmpeg-recreate-timestamps-without-reencoding/1358974
> 
> Tim

That's an intriguing idea, and as you say it could be decoder-dependent. 
  But it might be worth looking at the audio readahead setting:

Frontend setup > Video > Playback > Advanced Playback Settings >
   Audio read ahead (ms)

"Increase this value if audio cuts out frequently....."

Default is 100 ms.  On my GT 710 box it's at 400 ms.  I suppose I did that.

John P