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PostPosted: Fri Mar 03, 2006 3:01 am Reply with quote
xyzzy
 
Joined: 12 Feb 2006
Posts: 225




There is now a patch posted for the audio not getting detected bug. By offering increasingly more specific hints without actually offering any code, it was possible to fix the bug and still claim I was not the one who fixed it. I actually posted code that would make the auto-detection work better, so of course that can not be done, it must be done in a completely different manner.
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PostPosted: Sun Mar 05, 2006 11:23 pm Reply with quote
Scott Larson
 
Joined: 15 Oct 2003
Posts: 713
Location: Portland, OR




That was a rare case on the list where you (I think it was you) actually offered lots of interesting information so everyone could understand what was going on in the code. This is nice because the mplayer developers apparently frown on commenting their code, especially changes they make. That means you have ask the author of the code what the hell his code is doing, which means you have ask questions on the list and sound like a moron. They don't want to teach anyone about anything which sucks because that's the best way to get more developer working to improve the code.
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PostPosted: Mon Mar 06, 2006 11:36 am Reply with quote
logistiker
 
Joined: 09 Jan 2006
Posts: 10




Scott Larson wrote:
That was a rare case on the list where you (I think it was you) actually offered lots of interesting information so everyone could understand what was going on in the code.


I was wondering if you could post a link to this forum? I'd like to follow it.
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PostPosted: Sat Jun 24, 2006 10:34 am Reply with quote
logistiker
 
Joined: 09 Jan 2006
Posts: 10




I'm on Mplayer 1.0_pre8 now and it looks like this patch was FINALLY checked in so there aren't anymore CRC errors on any of my streams. Smile
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Re: Mplayer "a52: CRC check failed!" errors, any p
PostPosted: Sat Jun 24, 2006 1:26 pm Reply with quote
dcooppan
 
Joined: 07 Jun 2006
Posts: 1




Anonymous wrote:
I've seen that several people have been having problems with this.

I'm having the problem with local OTA Fox broadcasts. After a short while of trying to work, mplayer eventually craps out with repeated...

Code:
a52: CRC check failed!   -0.002 ct: -0.398 245/245 37% 13%  0.9% 0 0 10%
a52: CRC check failed!   -0.001 ct: -0.398 246/246 37% 13%  0.9% 0 0 11%
a52: CRC check failed!    0.005 ct: -0.339 307/307 36% 13%  0.9% 0 0 10%
a52: CRC check failed!    0.032 ct: -0.337 311/311 36% 13%  0.9% 0 0 10%


Errors, eventually giving me the list of potential problems.

If I use the -ao mpegpes option (which supresses audio), the video plays fine. I'm using the dvb drivers and apps (obviously). This seems to be an issue with (AC3) audio decoding on Fox, from what I've read.

As ABC also uses 720p, I doubt that it would have to do with 720p vs 1280i.

Has anyone with the a52: CRC errors had any resolution they'd care to share?



There is a temp fix for mplayer:
Explation of the problem:
"I think I have pinpointed the cause of some of these AC3 errors. It has to do
with the way the stations are encapsulating the AC3 inside the PES (Packetized
Elementary Stream, part of MPEG) packets. The problem is with my local FOX and
WB stations, like other people here have had problems with.

If you look at the mplayer-dev-eng mailing list for February you should be
able to follow the thread.

Most of the stations align the start of an AC3 frame with the start of a PES
packet. mplayer's TS demuxer looks at at the first bytes of the PES payload,
sees the AC3 syncword, and decides the packet is ac3 audio. This works.

Some stations doesn't align the start on an AC3 frame to the start of a PES
packet. I don't think the spec says they have to. When mplayer looks at the
start of the PES payload, it finds a random bit of data from the middle of an
AC3 frame. It dosen't know what this is and so tries to guess. If the first
four bits happen to be 1000, it will decide that the packet has some screwed
up DVD VOB file AC3 inside a TS stream non-standard format. mplayer will then
cut off four bytes it thinks are this DVD VOB header, but really they are four
bytes from the middle of an ac3 stream, and so this causes the CRC error.

There is a solution to solve the problem, which is to get mplayer to include
the PMT (program mapping table, says what PID has video,audio etc. and their
formats) in the data it requests from the DVB driver. To do this mplayer has
an extension to the channels.conf file. You should do something like this:
Code:
KCPQ-DT:567000000:QAM_256:33:34+32:1

In my case KCPQ has video on PID 33, audio on 34, and the PMT is on 32. You'll
have to figure out what the PIDs are for the PMT for each channel. Usually
it's 1 less than the pid of the video.

You can also run mplayer on the entire QAM channel. If it gets every single
PID, it will have the PAT and PMT. The output of getatsc is like this. I think
maybe using a PID of 0x2000 in channels.conf will do the same thing. It seems
that telling mplayer to scan the entire 40 Mbit/s QAM channel uses
significantly more CPU, so you probably don't want to use this method.

I could fix the TS demuxer so it would stop misdetecting this DVD VOB format,
but this would never be accepted into mplayer. As others have noted, the
mplayer dev clique is extremely hostile to any outside developer. If I submit
a patch, it will be bad because it was my idea and not theirs."

For FOX-HD there seems to be a problem with repeated ac3 headers - if one can now have mplayer look at PMT in addition to PID's for video and audio then the errors will get corrected. I recommend using "azap" to tune into a digital channel in question (fox-hd is tuned to 601780000 MHZ QAM on Comcast in Boston), use "dvbtraffic" to look at all the data streams bandwidth and pids, the low bandwidth say pid of about 21Kbits is what you want to try - put the decimal value of the pid (dvbtraffic uses hex numbers for pids) in the channels.conf file,

FOX-HD:601780000:QAM_256:2048:2049+48:1 eg:

The +48 is the PMT pid in decimal

Hope this helps,
Daya Cooppan [linux hd rocks!]
dcooppan@comcast.net
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