Re: [xine-devel] xine AC3 dropout problem - Please help!

[Reinhard N. <rn...@gm...>]

Hi,

Am 10.09.2010 18:27, schrieb VDR User:

>> System details are:
>>
>> debian testing
>> stable kernel 2.6.35.3 (quiet notsc clocksource=hpet)
>> gcc 4.4.4-8
>> alsa-base 1.0.23+dfsg-1
>> alsa-utils 1.0.23-2
>> xine-lib-1.2 hg r11577
>> xine-ui hg r3054
>> VDR-1.7.15
>> mplayer-nogui 2:1.0~rc3++svn20100804-0.0
>>
>> I recently tried the notsc and clocksource=hpet kernel options, which
>> also had no affect.  I want to reiterate that the dropout problem only
>> occurs in xine.  The error I see in the xine log when the dropout
>> occurs is: pcm_hw.c: snd_pcm_hw_delay() SNDRV_PCM_IOCTL_DELAY failed
>> (-32).
>>
>> I accidentally posted this to the alsa-dev mailing list and one of
>> their devs Jaroslav Kysela wound up responding to it with the
>> following:
>>
>>> -32 means -EPIPE - underrun has occured. It means that xine does not deliver
>>> samples in time to the driver for some reason. Because mplayer works, it
>>> does not seem like a general ALSA issue. I would ask xine developers for
>>> further debugging of this issue (compare the audio write calls with the
>>> realtime clock)."
> 
> Will someone PLEASE look into this.

Well, I was able to reproduce this issue with your supplied
.xine/config. The problem is caused by a too small number of
video input buffers (you used the default value of 500 buffers).

What is a reasonable buffer size?

When using vdr-xine to connect VDR to xine, each video input
buffer will get 2048 byte of the video stream. Given that your HD
channel broadcasts at 10 Mbit/s, you'll need that much buffers to
hold a single second of video:

10000000 bit  /  8 bit/byte  /  2048 byte/buffer  =  610 buffer

What about audio buffers. vdr-xine puts a single audio frame
(let's assume such a frame equals 24 ms of audio) into an audio
input buffer. So for a second of audio, you'll need that much
buffers:

1000 ms  /  24 ms/frame  /  1 frame/buffer  =  41 buffer

To allow an a/v offset at the input stage of up to +/-3 seconds,
you'll need 1831 video input buffers and 125 audio input buffers.
On top of that, you'll add another 2 seconds to allow for some
latency at the receiving and processing stages, so you'll end up
with 3051 video input buffers and 208 audio input buffers.

As you can see, 208 audio buffers is a bit less that what is the
default (230). But 3051 video buffers are much more than the
default (500).

The memory footprint of the above buffer counts is like that:
xine uses 8192 byte per input buffer, so you'll get

	3259 buffer  *  8 kbyte/buffer  =  26072 kbyte

or roughly 25 MB.

The actual number of input buffers may be chosen a bit lower as a
part of the a/v offset can also be buffered during decoding and
by the output buffers.

Bye.
-- 
Dipl.-Inform. (FH) Reinhard Nissl
mailto:rn...@gm...