Re: [Mvpmc-users] AC3 trouble

[Bernhard G. <ge...@ge...>]

stuart <stuart@...> writes:

> We gave up a long time ago with playing the audio recorded OTA on ATSC 
> stations directly.  I see you are not in the states so I don't know what 
> may or may not work for you.  I had thought many had resorted to 
> transcoding their video on the fly using VLC when serving them up to a 
> mediaMVP box.  At one time I had thought I would schedule transcoding 
> everything I recorded on my mythtv setup to a lower quality bit rate and 
> stereo format (compatible with mvpmc).  But I never got around to it.  
> And now I feel I would be giving something up on the front ends that can 
> handle the higher fidelity video and sound.

Finding a new front end does not seem to be that easy, looks like any media
player has some flaws. I also tend not to dump things that are still working,
but try to fix them.
 
> I am not familiar with feeds that contain both the MPEG2 audio and AC3 
> audio.  But I am siding with the thought that the mediaMVP box may not 
> have enough Ethernet bandwidth to keep up with so much data.

Here's a sample: ftp://patriciawindt.dyndns.org/mvpmc/badVideo1.mpg
I'm pretty sure it's not the bandwidth, other videos with even higher bit rates
play fine. To mee it looks like something's broken with the demuxer.
mvpmc doesn't even detect the right audio streams for some recordings, saying
"PCM" instead of "AC-3".

> I would suggest you google and hunt down the "recipes" for transcoding 
> on the fly when the client is the mvpmc.  It has been done and I am sure 
> you will find several descriptions on how to do this.  At that point you 
> can probably get rid of the AC3 component of the stream if that is what 
> is giving you problems.

That's what I have done now - although this way I cannot watch while the
recording is still running. Didn't find a working existing solution, mencoder
has some sync issues with TS streams, ffmpeg cannot handle most of them at all.
Had to use projectx and mediainfo. Here's the (shortened) MythTV user script.
It takes a PS or TS stream as input and writes all MPEG audio & video streams
into a MPEG PS file, omitting all other streams:


#!/bin/sh
VIDEODIR=$1 # Parameter 1: %VIDEODIR%
FILENAME=$2 # Parameter 2: %FILENAME%

TEMPDIR="/home/mythtv/tmp/"
WORKDIR=`mktemp -d --tmpdir="${TEMPDIR}"` || exit 1
DISPLAY=""

# required parameters
[ -z "$VIDEODIR" -o -z "$FILENAME" ] && exit 1	
# source file must exist
[ ! -f "$VIDEODIR/$FILENAME" ] && exit 1	

# look for ac3 audio: none found? -> we're done!
mediainfo --Language=raw "$VIDEODIR/$FILENAME" | grep -q "^Format.*AC-3" \
   || exit 0

# get ids for MPEG video & audio streams
IDS=`mediainfo --Language=raw "$VIDEODIR/$FILENAME" \
  | grep -B 2  -e "^Format.*: MPEG Audio$"  -e "^Format.*: MPEG Video$" \
  | grep "^ID" | awk 'BEGIN {ORS=","}{print $3}'`

# any mpeg streams found?
[ z == ${IDS}z ] && exit 1	

# create a mpeg-ps using just the MPEG streams
projectx -tom2p -out "${WORKDIR}" -name projectx -id ${IDS} "$VIDEODIR/$FILENAME"

# "find" projectx generated file
NEWFILE=`find "$WORKDIR" -type f -name "projectx*mpg"`

# either file not found or filesize=0
[ ! -s "$NEWFILE" ] && exit 1 

# replace source file
mv "$NEWFILE" "$VIDEODIR/$FILENAME" && rm -r "${WORKDIR}"