Mythfrontend crash on local broadcasts

[Håkon Alstadheim <hakon@…>]

Mythfrontend crashes whenever I try to play a local broadcast, or a broadcast directly preceding or following such.

Background:
In DVB-T in Norway local broadcasts are sent with different identifiers in the stream from what the channel shows the rest of the day. This used to crash in early 0.24, until it was fixed. Now in current head it has been broken since I can remember. This failure mode might be a regression from ticket #6703 , it is the same programmes and the same channel that is failing again, i.e. a recordings containing switch-over from one PID to another.

To illustrate the phenomenon, running this:

for f in *.mpg ; do
    CHANID=$(echo -n $f |sed -e 's/_.*/ /' )
    echo -n "$CHANID"
    mplayer -tsprobe 10000000 -frames 0 -identify  $f 2>/dev/null| grep -m 1 -e '^VIDEO' || echo $f error
done| sort -u

On one of my recording directories, gives this (blank lines added and old channel-ids removed for clarity)

1102 VIDEO H264(pid=525) AUDIO AAC LATM(pid=692) SUB Teletext(pid=576)  PROGRAM N. 1
1102 VIDEO H264(pid=525) AUDIO AAC LATM(pid=693) SUB Teletext(pid=576)  PROGRAM N. 1

1103 VIDEO H264(pid=521) AUDIO AAC LATM(pid=676) SUB Teletext(pid=576)  PROGRAM N. 1
1103 VIDEO H264(pid=521) AUDIO AAC LATM(pid=677) SUB DVB(pid=604)  PROGRAM N. 1
1103 VIDEO H264(pid=521) AUDIO AAC LATM(pid=677) SUB Teletext(pid=576)  PROGRAM N. 1

2009 VIDEO H264(pid=512) AUDIO AAC LATM(pid=640) SUB Teletext(pid=576)  PROGRAM N. 1
2009 VIDEO H264(pid=512) AUDIO AAC LATM(pid=641) SUB Teletext(pid=576)  PROGRAM N. 1
2009 VIDEO H264(pid=515) AUDIO AAC LATM(pid=652) SUB Teletext(pid=576)  PROGRAM N. 1
2009 VIDEO:  [DVSD]  720x480  24bpp  29.970 fps    0.0 kbps ( 0.0 kbyte/s)

Channel 2009 gives recordings that cause crashes.

I have a sample of the start of a crashing recording here:

<​http://alstadheim.priv.no/midnytt-start-til-bt.mpg> (10Mb) (note: it is on a slow home ADSL-line with a dynamic IP-address)

I am running

Package: mythtv-frontend
Maintainer: MythTV Ubuntu Maintainers <ubuntu-mythtv@lists.ubuntu.com>
Architecture: i386
Version: 2:0.25.0~master.20111121.4f506d0-0ubuntu0mythbuntu3

4f506d0 refers to git commit

I will attach a terminal capture from the run (with myth output) and a gdb log with a backtrace (and a full thread backtrace) They can be found here aswell <​http://alstadheim.priv.no/mythfrontend-crash-run-stdout.txt> <​http://alstadheim.priv.no/mythfrontend-backtrace.log>

[Håkon Alstadheim <hakon@…>]

Standard output from a crashing run of mythfrontend

[Håkon Alstadheim <hakon@…>]

gdb log with backtraces of crashing run of mythfrontend

[markk]

fwiw - this plays back perfectly on several systems here with latest master.

[JYA]

I can see from the log what is happening, though I have no idea why it is happening nor can I reproduce it here with the provided sample

[JYA]

Fix attempt

[JYA]

Please check with the provided fix if it's working for you. I unfortunately can't test as my amplifier is being serviced at present

[Håkon Alstadheim <hakon@…>]

I now have done "apt-get build-dep mythtv", "apt-get source mythtv", "dpkg-buildpackage -b" , and noticed a missing build dependency in the mythbuntu package, viz libx264-dev. Installing that and building WITHOUT your fix, results in a WORKING SYSTEM ?

Now, the source i get is marked with commit tag cc1314d, whereas the prebuilt one is 4f506d0, which dates from November 20, 2011. I think you can chalk this down as FIXED, (if not, it is some quirk in the Mythbuntu build system that creates a subtly broken .deb). If this returns when Mythbuntu catches up with me, I'll know to contact the builder first :-/ :-)

P.S: Downgrading brings the crash back.

Faithfully yours (and this time I mean it) Håkon A.

[Håkon Alstadheim <hakon@…>]

Sorry to have rejoiced a bit too soon. It just takes a longer sample now to provoke the crash, and it is now possible to skip past the crashing switchover.The frontend used to die immediatly when starting playback. This sample: <​http://alstadheim.priv.no/midtnytt-eksempel.mpg> (555M, 0.25mbit/s uplink ) still provokes a crash. at:

Program received signal SIGFPE, Arithmetic exception.
[Switching to Thread 0x925feb70 (LWP 16478)]
0x0057aaaa in AvFormatDecoder::ProcessAudioPacket (this=0x9b020480, 
    curstream=0x8dfcc20, pkt=0xa320c3f0, decodetype=kDecodeAudio)
    at avformatdecoder.cpp:4053
4053                     av_get_bits_per_sample_fmt(ctx->sample_fmt)>>3);
#0  0x0057aaaa in AvFormatDecoder::ProcessAudioPacket (this=0x9b020480, 
    curstream=0x8dfcc20, pkt=0xa320c3f0, decodetype=kDecodeAudio)
    at avformatdecoder.cpp:4053

The switchover/crash occurs ~1 minute into the recording.

The patch provided above (​http://code.mythtv.org/trac/attachment/ticket/10183/10183fix.diff) makes the frontend survive that switchover.

[Håkon Alstadheim <hakon@…>]

backtrace after crash with MythTV Version : v0.25pre-3827-gcc1314d

[JYA]

so you're saying that the patch provided fix it ?

[Håkon Alstadheim <hakon@…>]

THIS TIME I will not jump the gun, but I have not found a recording that will crash myth whith the patch applied. It takes a while before the artefacts disappear after the switchover though.

[JYA]

Fixed in SHA1:d6dcd42d446eef0630c0ccee8ee159dcebd5c540

Note that the underlying issue isn't in Myth ; we now just cater for a case that should never have happened in the first case

[Håkon Alstadheim <hakon@…>]

Much obliged. mplayer and vlc have consistently been able to play the problem-recordings though :->

I will redo the tests with&without the patch on the mythbuntu build that came out today (MythTV Version : v0.25pre-3838-gdbd0cc0, from commit gdbd0cc0) . I can still provoke the crash on the prebuilt ones, I'll see tonight if the patch still helps on that new test-case.

[Håkon Alstadheim <hakon@…>]

Yes. With the patch in 10183fix.diff applied, the frontend survives the switchover.