[mythtv-users] Jitters during playback

[Wil]

On 12-01-28 11:15 AM, Michael T. Dean wrote:
..
> FWIW, I had been getting a lot of OTA recordings that showed
> "jitters/pixelation" during playback.  When I switched my profile from
> VDPAU decode + VDPAU render to ffmpeg decode + VDPAU render, all the
> issues went away.  I don't think it's a problem with MythTV code, but a
> problem with VDPAU's ability to cope with small errors in the stream due
> to small signal issues.

I did the same thing too for the same reason after upgrading to VDPAU. It
did provoke me to investigate a bit at the time. 

I created this script to help. It requires ffmpeg and redirects output to a
log file (used to cache results). The filename of the mpeg file you want to
scan needs to be the 1st parameter to the script. It prefers an ac3 eng
audio stream over an mp2 eng audio stream if present. I'm not sure if it
will select the appropriate audio stream for streams different to the ones I
used for testing (will probably fail if it doesn't find a matching audio
stream). You would need to adjust it if you want to select a different
language or whatever anyway. There is usually damage at the start and end of
the streams.

#!/bin/bash

if ffmpeg -v 5 -i "$1" -ar 48000 -ac 2 -f null -y /dev/null -t 0 2>&1 | grep
eng | grep -q ac3 
then
	STM=`ffmpeg -v 5 -i "$1" -ar 48000 -ac 2 -f null -y /dev/null -t 0
2>&1 | grep eng | grep ac3 | sed -n 's/.*Stream #\([0-9]\.[0-9]\).*/\1/p'`
	echo "AC3 Stream: $STM"
else
    STM=`ffmpeg -v 5 -i "$1" -ar 48000 -ac 2 -f null -y /dev/null -t 0 2>&1
| grep eng | grep mp2 | sed -n 's/.*Stream #\([0-9]\.[0-9]\).*/\1/p'`
    echo "MP2 Stream: $STM"
fi

FN="$1.scan.log"

if [ -f $FN ]
then
	echo "using scan log $FN"
else
	ffmpeg -v 5 -i "$1" -ar 48000 -ac 2 -map 0.0 -map $STM -f null -y
/dev/null > $FN 2>&1
fi

cat "$FN" | sed 's/\r/\r\n/g' | sed 's/\*\*\* .* dup!//' | sed '/^$/d' |
grep --color=always -vn "frame" -B 1

----------------

It might be worth experimenting with transcoding your streams. Maybe also
try the ffmpeg list and see if someone can suggest an easy way to do it
there.

Will