[mythtv-users] Intermittent playback skips and log errors

Mark Lord mythtv at rtr.ca
Mon Nov 28 15:56:53 UTC 2011

On 11-11-27 09:47 AM, steve wrote:
> On 11/25/2011 9:35 PM, Mark Lord wrote:
>> On 11-11-25 12:19 PM, steve wrote:
>>> I am having a problem playing back recorded (via HDPVR) shows.  There is
>>> intermittent dropping out of audio and perhaps a brief skip in the video
>>> then playback continues.  The log is filled with hundreds of entries like
>>> 2011-11-22 06:42:11.701 [h264 @ 0x35326f4f20]non-existing PPS referenced
>>> 2011-11-22 06:42:11.701 [h264 @ 0x35326f4f20]sps_id out of range
>>> 2011-11-22 06:42:11.701 [h264 @ 0x35326f4f20]non-existing SPS 32 referenced in b
>>> uffering period
>>> 2011-11-22 06:42:11.701 [h264 @ 0x35326f4f20]non-existing PPS 0 referenced
>>> 2011-11-22 06:42:11.701 [h264 @ 0x35326f4f20]decode_slice_header error
>>> 2011-11-22 06:42:11.701 [h264 @ 0x35326f4f20]no frame!
>>> 2011-11-22 06:42:11.753 [h264 @ 0x35326f4f20]mmco: unref short failure
>>> I researched this, and it seems to be related to VDPAU somehow, but I can't find any consistent recommendation for a fix.  I have the latest NVIDIA drivers installed.  Anyone have idea about how to address this?
>> I've noticed this *began* happening for some h264 files on my own system
>> at some point this fall.  I regularly build mythtv from the latest 0.24-fixes
>> sources,
>> and until perhaps July/August 2011 everything was fine on the stuttering front.
>> But as of October, some files that used to play perfectly now have the issue.
>> A workaround I've found for it is to enable "-v all" logging for mythfrontend.
>> That's right -- turn on all of the debug messages to try and track down the issue,
>> and the issue itself goes away.  For me at least.  :)
> Thanks but I tried this fix and it didn't work for me.  It's odd because 
> some recordings play just fine, whereas others stutter so much it's 
> difficult to watch them.  I've tried lowering number of backend jobs to 
> 1 and setting processor load to low in setup in case it's a processor 
> issue, but nothing seems to affect it.

Yeah, I poked around with it some more last night and discovered
that the logging trick worked only for a couple of videos that
had only minor audio loss issues.

Lots of other videos still had intermittent audio regardless.
So I checked with mediainfo on those, and discovered that all of
the jerky-audio files were used AAC for audio, at bit rates > 100kb/sec.

So I figure the issue has to do with bad AAC decoding or something in mythtv
or in the libraries it uses for AAC.

Easy fix:  run ffmpeg to convert the audio tracks to AC3.
I wrote a shell script to do this last evening, and the results
are just fine -- everything I tried it on was instantly cured.

Here's the script.  Requires the "mediainfo" command.
Feed it a list of video path/filenames as input.
Output is to same_name.avi, or same_name-new.avi if old file was a .avi:

# Fix stuttering audio:

while [ "$1" != "" ]; do
        aformat=$(mediainfo --inform="Audio;%Format%" "$f")
        if [ "$aformat" = "AAC" ]; then
                [ "$f" = "$out" ] && out="$fname-new.avi"
                ffmpeg -i "$f" -vcodec copy -acodec ac3 -ab 384k "$out"
                echo "$f: not AAC, skipped ($aformat)"

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