[mythtv-users] Live TV: Too fast now ?

[Roger Siddons]

I've just got around to trying out 0.27 (clean install of Mythbuntu  
14.04.1/0.27.3) and obviously wanted to check out JYA's Live TV  
improvements, even though we don't use it very often.

*When* it works, it's a great improvement - channel changes are fast &  
reliable. So thanks JYA for all your hard work.

However, overall the WAF factor is worse because;

1. When starting Live TV it fails 60% of the time - "Could not open  
decoder"

2. When it works, switching tuner source fails 90% of the time. Although a  
feature of minor importance, I find it useful for checking all tuners are  
working properly.

The debug/playback frontend log of successfully starting Live TV, then  
switching source is at http://paste.ubuntu.com/8071453/.

It appears as though the frontend is quick to abort Live TV because ffmpeg  
can't determine the (audio?) codec. However this failure did produce a  
(damaged) recording that played fine from 'Watch Recordings' - all 2.5 s  
of it.

$ mythffmpeg -i /var/lib/mythtv/livetv/1004_20140817130826.mpg

ffmpeg version 1.2.7 Copyright (c) 2000-2014 the FFmpeg developers
built on Aug 11 2014 23:51:16 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
configuration: --compile-type=profile --prefix=/usr --runprefix=/usr  
--disable-mythlogserver --enable-crystalhd --enable-lirc  
--enable-audio-alsa --enable-audio-oss --enable-dvb --enable-ivtv  
--enable-firewire --enable-joystick-menu --with-bindings=perl  
--enable-ffmpeg-pthreads --enable-pic  
--perl-config-opts='INSTALLDIRS=vendor' --enable-libvpx --enable-sdl  
--enable-libmp3lame --enable-libx264 --enable-opengl-video --enable-vaapi  
--enable-vdpau
libavutil 52. 18.100 / 52. 18.100
libavcodec 54. 92.100 / 54. 92.100
libavformat 54. 63.104 / 54. 63.104
libavdevice 54. 3.103 / 54. 3.103
libavfilter 3. 42.103 / 3. 42.103
libswscale 2. 2.100 / 2. 2.100
libswresample 0. 17.102 / 0. 17.102
libpostproc 52. 2.100 / 52. 2.100
[dvbsub @ 0xee09a0] Invalid extradata, subtitle streams may be combined!
[mpegts @ 0xedba20] write_section_data: PID 0x898 CRC error
[mpeg2video @ 0xede980] 0x0 is invalid
Last message repeated 19 times
[mpegts @ 0xedba20] PES packet size mismatch
Last message repeated 1 times
[NULL @ 0xee09a0] start time is not set in estimate_timings_from_pts
[NULL @ 0xee25c0] start time is not set in estimate_timings_from_pts
[mpegts @ 0xedba20] write_section_data: PID 0x898 CRC error
Last message repeated 2 times
[mpegts @ 0xedba20] PES packet size mismatch
Last message repeated 1 times
Input #0, mpegts, from '/var/lib/mythtv/livetv/1004_20140817130826.mpg':
Duration: 00:00:02.53, start: 70302.141778, bitrate: 3257 kb/s
Stream #0:0[0x44d]: Video: mpeg2video (Main), yuv420p, 720x576 [SAR 64:45  
DAR 16:9], 25 fps, 25 tbr, 90k tbn, 50 tbc
Stream #0:1[0x44e](eng): Audio: mp2, 48000 Hz, stereo, s16p, 192 kb/s
Stream #0:2[0x44f](eng): Audio: mp2, 48000 Hz, mono, s16p, 64 kb/s
Stream #0:3[0x46b](eng): Subtitle: dvb_subtitle
Stream #0:4[0x898]: Data: dsmcc_b

I'm guessing this is because my old tuners (KWorld UB499-2T & AverMedia  
771 on UK OTA) are too slow to tune/settle and ffmpeg can't interpret the  
garbage they start up with when there's so little data. However the tuners  
are reliable and do produce perfect recordings and so I'm looking for a  
way to slow down Live TV's startup or make it more tolerant.

A "DVB tuning delay" of 6000 ms (poked manually as mythtv-setup is still  
broken) doesn't have any effect (except it waits 6s before failing) so I  
presume the extra delay doesn't produce any more/better data.  
Interestingly this only seems to be respected on Live TV start-up:  
switching input source to a tuner with a tuning delay set fails quickly  
with no delay.

For "Quick tuning":  "Always" seems to be better than "Never" but doesn't  
solve the issue.

Likewise "Wait for Seq Header: Off" seems to reduce the failure rate, but  
not significantly.

So, questions:

1. Are there any other settings that would have an impact ?

2. Live TV always appears to check RAM for 1500 ms before checking the  
file. Are there any settings/ways to increase this ?

3. Is it feasible/desirable for Live TV to re-examine the file  
periodically before giving up ? If the file exists/is growing then isn't  
there a chance that ffmpeg might eventually succeed. A long pause is  
preferable to a failure. And if you're trying to watch Live TV with a duff  
tuner then a delay of 10s before raising an error doesn't seem  
unreasonable to me.

4. What's the best way to inspect the tuner data, ie. determine why ffmpeg  
isn't happy ? Would ProjectX help ?
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