Weird Audio clipping from my local WB

[WannaB]

Hi folks,

I've got a MyHD card. I tried to cap an old Outer Limits episode yesterday from my local WB station and everything seemed to go fine but I ended up with the audio being clipped throughout. So I open up the MyHD app and tune to the station and sure enough I hear clipped audio. All the other stations sound fine. But then an actual WB network program comes on (one of their sitcoms) and it sounds fine. When it goes to commercial, some of the commercials sound clipped and some of them sound fine. I'm now thinking the problem is actually with the local broadcaster. Their network feed sounds fine but their purely local broadcasts sound clipped. It only happens on their digital feed, the analog feed seems to be fine.

Anyone ever encounter anything like this before or know of an explanation as to why this might be happening?

I'm going to call them up and tell them what I'm experiencing, but I don't want to sound too stupid. Even though nothing has changed on my end and I've capped dozens of shows from that station before without any problems, could the problem still lie with my equipment somehow?

Thanks for any opinions and advice.

[eb]

It seems to me that the problem is connected with your audio decoding capabilities, most probably it is problem with decoding AC3 5.1.
Please give more details about your audio decoders.

eb

[WannaB]

I'm not sure exactly what the MyHD application uses to decode the audio or how to find out. It's the app that comes with the MyHD MDP-120 card. But it has worked perfectly for the past 3 or 4 months on that station, and it still works perfectly on all other stations. And also, like I said, it seems to work perfectly on WB network broadcasts, it's only when they switch to a locally originating broadcast that the audio gets seriously clipped. I think if the decoder were bad, it would never have worked or that if it had somehow gotten corrupt or damaged, the problem would be showing up on all stations and during all feeds. Also, nothing has changed on my system recently. I haven't installed/uninstalled any new apps or codecs or anything recently.

I'd assume the problem is more likely to be on my end, but since nothing has changed here and since the problem seems kind of peculiar, the next guess is that it has to be originating with the broadcaster, but I just don't know.

[eb]

@ WannaB,
try to record 5MB of this show and check this record with bbtool1.9.
or upload this sample somwhere

eb

[WannaB]

Okay, I've played around with bbtools. It's not really giving me any information I know what to do with. But if I demux and convert the ac3 stream to wave using HeadAC3, caps of what I'm calling "locally originating" broadcasts have clipped audio, caps of "network originating" broadcasts are perfect.

And again, it's just this one station. All other stations are perfect. It's really weird. I tried calling the station today but I couldn't get a hold of anyone. I'll try again tomorrow.

Oh, and this station has a subchannel (which I think is for Spanish audio when available). There's no clipping on that subchannel.

Thanks for the input.

[eb]

I expected that you can deliver informations as example:

Summary:

MPEG Transport Packets = 928248
PID 0000, Program Association Table packets = 633, total bytes = 116472
PID 0A02, MPEG Audio stream 0 packets = 21127, total bytes = 3744348
PID 0A05, MPEG Audio stream 8 packets = 20802, total bytes = 3744352
PID 0A0F, Other packets = 1248, total bytes = 229632
PID 0A11, Video stream 0 packets = 807517, total bytes = 148085775
PID 0A12, Private Stream 1 packets = 54603, total bytes = 9695907
PID 0A2C, Other packets = 1723, total bytes = 317032
PID 0B25, Other packets = 20595, total bytes = 3789480

but you are frugal to present some details,
sorry for the wasted time

eb

[WannaB]

I mostly haven't understood what you've been asking because your questions have been a little too general for me. How's this then:

Summary:

MPEG Transport Packets = 36864
PID 0x0000, Program Association Table packets = 34, total bytes = 6256
PID 0x0020, Other packets = 33, total bytes = 6072
PID 0x0021, Video stream 4 packets = 27355, total bytes = 5016036
PID 0x0024, Private Stream 1 packets = 373, total bytes = 68440
PID 0x0025, Private Stream 1 packets = 373, total bytes = 68440
PID 0x0030, Other packets = 34, total bytes = 6256
PID 0x0040, Other packets = 34, total bytes = 6256
PID 0x1D07, Other packets = 39, total bytes = 7176
PID 0x1D08, Other packets = 24, total bytes = 4416
PID 0x1D09, Other packets = 20, total bytes = 3680
PID 0x1D0A, Other packets = 19, total bytes = 3496
PID 0x1D87, Other packets = 12, total bytes = 2208
PID 0x1D88, Other packets = 1, total bytes = 184
PID 0x1D89, Other packets = 7, total bytes = 1288
PID 0x1D8A, Other packets = 4, total bytes = 736
PID 0x1FFB, Other packets = 95, total bytes = 17480
PID 0x1FFF, Null packets = 8407, total bytes = 1546888

I know that PIDs 24 & 25 are the audio streams.

[eb]

Your analysis is from too short record , but having ratio audio to video data like 1:70 i can assume that in this case your audio can be mono type, and in this case not every codec is working good with mono audio.

eb

Please demux PIDs 24 and 25 with bbdmux command and play back with mplayer2 from WMP folder and look for properties of this audio.

edited: or better way demux with ProjectX then you get more informations about the rest of the PIDs.

[WannaB]

Okay, here are the log files from two different clips demuxed with Project X. The first is a "network" broadcast where the audio sounds perfect and the second is a "locally originating" broadcast where the audio is clipped. It looks to me like the two are basically the same, but I'm definitely inexperienced at looking at this kind of thing. I hope this is more useful to you.

******** Network Good Audio**************


ProjectX 0.81.7_int01 (16.04.2004)

=== session infos ===

=> working with collection 0
-> write output files to :
C:\Capture\test\

=> File 0: C:\Capture\test\0817-204455.tp (67379200 bytes)
=> File is DVB/MPEG-2 TS (Video/Audio/TTX PES)
=> demux
-> SID 0x2
-> PMT 0x20 refers to these usable streams:
Video PIDs: 0x21
Audio PIDs: 0x24(AC-3)(eng)_PD 0x25(AC-3)(spa)_PD
Teletext PIDs:

--> PID 0x1FFF => stuffing packet -> ignored
ok> PID 0x21 has PES-ID 0xE4 (MPEG Video) (0xEB0 #21)
--> PID 0x20 (PMT) (0x1903C #546) -> ignored
--> PID 0x40 (PMT) (0x1F594 #684) -> ignored
--> PID 0x1D85 (payload: 00 CC F0 A3 00 00 D1 00 ..) (0x23110 #765) -> ignored
--> PID 0x0 (PAT) (0x25E98 #827) -> ignored
--> PID 0x1D06 (payload: 00 CB F1 C0 00 03 D1 00 ..) (0x29434 #900) -> ignored
--> PID 0x30 (PMT) (0x2C3F0 #965) -> ignored
--> PID 0x1D05 (payload: 00 CB F1 36 00 03 D1 00 ..) (0x2F98C #1038) -> ignored
--> PID 0x1FFB (payload: 00 C7 F2 34 00 00 D5 00 ..) (0x361D4 #1180) -> ignored
ok> PID 0x24 has PES-ID 0xBD (private stream 1) (0x560F4 #1876)
ok> PID 0x25 has PES-ID 0xBD (private stream 1) (0x63764 #2168)
--> PID 0x1D07 (payload: 00 CB F0 0B 00 01 D1 00 ..) (0x63A54 #2172) -> ignored
--> PID 0x1D08 (payload: 00 CB F1 D2 00 02 CB 00 ..) (0x8060C #2798) -> ignored
-> video basics: 1920*1088 @ 29.97fps @ 0.7031 (16:9) @ 13990000bps, vbvBuffer 427
-> starting export of video data @ GOP#0
!> dropping useless B-Frames @ GOP#0 / new Timecode 00:00:00.000
--> PID 0x1D86 (payload: 00 CC F0 45 00 00 D1 00 ..) (0x207284 #11312) -> ignored
--> PID 0x1D87 (payload: 00 CC F0 BC 00 00 D1 00 ..) (0x20DACC #11454) -> ignored
--> PID 0x1D88 (payload: 00 CC F0 92 00 00 CB 00 ..) (0x28ED54 #14268) -> ignored
--> PID 0x1D00 (payload: 00 CB F0 0B 00 01 D5 00 ..) (0x3A99D00 #326849) -> ignored
--> PID 0x1D01 (payload: 00 CB F0 0B 00 01 D5 00 ..) (0x3ED00F0 #350341) -> ignored
--> PID 0x1D02 (payload: 00 CB F0 0B 00 01 D3 00 ..) (0x3EF389C #351114) -> ignored
--> PID 0x1D03 (payload: 00 CB F0 0B 00 01 D3 00 ..) (0x3F34124 #352520) -> ignored
--> PID 0x1D04 (payload: 00 CB F0 0B 00 01 D3 00 ..) (0x4032FDC #358074) -> ignored
packs: 272432 100% 67379200

-> video: fr/ ct/ 1p/ cg/ og/ dg = 808/ 1/ 0/ 54/ 0/ 0
-> video length: 808 frames @ 00:00:26.960
-> GOP summary: min. 26, max. 30 fields; contains interlaced frames
-> avg. nom. bitrate 14101119bps (min/max: 12854400/14798400)
-> set first sequence_header bitrate to 9800000bps
===> new File: C:\Capture\test\0817-204455.mpv

--> AC-3/DTS Audio on PID 0x24
Audio PTS: first packet 06:56:52.880, last packet 06:57:20.304
Video PTS: start 1.GOP 06:56:53.416, end last GOP 06:57:20.376
-> adjusting audio at video-timeline
!> missing syncword @ 0, @ 00:00:00.000
!> found syncword @ 144
=> src_audio: AC-3, CM, 2/0(2.0), 48000Hz, 192kbps @ 00:00:00.000
audio frames: wri/pre/skip/ins/add 842/0/0/0/0 @ 00:00:26.944 done..
===> new File: C:\Capture\test\0817-204455.ac3

--> AC-3/DTS Audio on PID 0x25
Audio PTS: first packet 06:56:52.919, last packet 06:57:20.087
Video PTS: start 1.GOP 06:56:53.416, end last GOP 06:57:20.376
-> adjusting audio at video-timeline
!> missing syncword @ 0, @ 00:00:00.000
!> found syncword @ 416
=> src_audio: AC-3, CM, 1/0(1.0), 48000Hz, 192kbps @ 00:00:00.000
-> 4 frame(s) (128ms) added @ 00:00:26.848
audio frames: wri/pre/skip/ins/add 843/0/0/0/4 @ 00:00:26.976 done..
===> new File: C:\Capture\test\0817-204455_1.ac3

summary of created media files:
.Video (m2v): 808 Frames 00:00:26.960 C:\Capture\test\0817-204455.mpv
Audio 0 (ac3): 842 Frames 00:00:26.944 0/0/0/0 C:\Capture\test\0817-204455.ac3
Audio 1 (ac3): 843 Frames 00:00:26.976 0/0/0/4 C:\Capture\test\0817-204455_1.ac3
=> 48814852 bytes written...

************* Local Bad Audio *****************

ProjectX 0.81.7_int01 (16.04.2004)

=== session infos ===

=> working with collection 0
-> write output files to :
C:\Capture\test\

=> File 0: C:\Capture\test\0817-224536.tp (31379456 bytes)
=> File is DVB/MPEG-2 TS (Video/Audio/TTX PES)
=> demux
-> SID 0x2
-> PMT 0x20 refers to these usable streams:
Video PIDs: 0x21
Audio PIDs: 0x24(AC-3)(eng)_PD 0x25(AC-3)(spa)_PD
Teletext PIDs:

--> PID 0x1FFF => stuffing packet -> ignored
--> PID 0x20 (PMT) (0x1A70 #37) -> ignored
--> PID 0x1D81 (payload: 00 CC F0 94 00 00 D5 00 ..) (0x52FC #114) -> ignored
--> PID 0x40 (PMT) (0x82B8 #179) -> ignored
ok> PID 0x21 has PES-ID 0xE4 (MPEG Video) (0x87DC #186)
--> PID 0x1D05 (payload: 00 CB F0 0B 00 01 D1 00 ..) (0xB564 #248) -> ignored
--> PID 0x0 (PAT) (0xE810 #317) -> ignored
--> PID 0x1D06 (payload: 00 CB F0 0B 00 01 D1 00 ..) (0x11DAC #390) -> ignored
--> PID 0x30 (PMT) (0x15114 #460) -> ignored
--> PID 0x1FFB (payload: 00 C8 F1 04 02 85 CD 00 ..) (0x183C0 #529) -> ignored
ok> PID 0x24 has PES-ID 0xBD (private stream 1) (0x19B40 #561)
ok> PID 0x25 has PES-ID 0xBD (private stream 1) (0x2A5D4 #924)
--> PID 0x1D82 (payload: 00 CC F0 60 00 00 D3 00 ..) (0x5F83C #2082) -> ignored
--> PID 0x1D07 (payload: 00 CB F0 0B 00 01 D1 00 ..) (0x10A70C #5806) -> ignored
--> PID 0x1D86 (payload: 00 CC F0 45 00 00 D1 00 ..) (0x117A8C #6094) -> ignored
--> PID 0x1D08 (payload: 00 CB F0 0B 00 01 CB 00 ..) (0x147DA4 #7144) -> ignored
--> PID 0x1D83 (payload: 00 CC F0 64 00 00 D3 00 ..) (0x1583D0 #7501) -> ignored
--> PID 0x1D87 (payload: 00 CC F0 51 00 00 D1 00 ..) (0x161F80 #7713) -> ignored
-> video basics: 1920*1088 @ 29.97fps @ 0.7031 (16:9) @ 13990000bps, vbvBuffer 427
-> starting export of video data @ GOP#0
!> dropping useless B-Frames @ GOP#0 / new Timecode 00:00:00.000
--> PID 0x1D88 (payload: 00 CC F0 92 00 00 CB 00 ..) (0x240938 #12563) -> ignored
--> PID 0x1D84 (payload: 00 CC F0 89 00 00 D3 00 ..) (0x26DBD8 #13547) -> ignored
--> PID 0x1D85 (payload: 00 CC F0 5F 00 00 D1 00 ..) (0x3D73C8 #21423) -> ignored
--> PID 0x1D89 (payload: 00 CC F0 7E 00 00 CB 00 ..) (0x414A60 #22761) -> ignored
--> PID 0x1D8A (payload: 00 CC F0 6A 00 00 CB 00 ..) (0x47253C #24802) -> ignored
--> PID 0x1D8B (payload: 00 CC F0 67 00 00 CB 00 ..) (0x5A1C30 #31413) -> ignored
--> PID 0x1D8C (payload: 00 CC F0 51 00 00 CB 00 ..) (0x63FD60 #34857) -> ignored
--> PID 0x1D8D (payload: 00 CC F0 5D 00 00 CB 00 ..) (0x792EF0 #42245) -> ignored
--> PID 0x1D8E (payload: 00 CC F0 68 00 00 CB 00 ..) (0x851464 #46392) -> ignored
--> PID 0x1D8F (payload: 00 CC F0 59 00 00 CB 00 ..) (0x9873A0 #53145) -> ignored
--> PID 0x1D90 (payload: 00 CC F0 59 00 00 CB 00 ..) (0xB7204C #63838) -> ignored
--> PID 0x1D91 (payload: 00 CC F0 A5 00 00 CB 00 ..) (0xCD199C #71498) -> ignored
--> PID 0x1D92 (payload: 00 CC F0 62 00 00 CB 00 ..) (0xDD0B44 #77056) -> ignored
--> PID 0x1D93 (payload: 00 CC F0 32 00 00 CB 00 ..) (0xE0462C #78182) -> ignored
--> PID 0x1D94 (payload: 00 CC F0 64 00 00 CB 00 ..) (0xE98C68 #81415) -> ignored
--> PID 0x1D95 (payload: 00 CC F0 CC 00 00 CB 00 ..) (0xFE87A0 #88729) -> ignored
--> PID 0x1D96 (payload: 00 CC F0 4E 00 00 CB 00 ..) (0x10495E4 #90840) -> ignored
--> PID 0x1D97 (payload: 00 CC F0 4F 00 00 CB 00 ..) (0x11827CC #97662) -> ignored
packs: 126874 100% 31379456

-> video: fr/ ct/ 1p/ cg/ og/ dg = 367/ 1/ 0/ 25/ 0/ 0
-> video length: 367 frames @ 00:00:12.240
-> GOP summary: min. 18, max. 30 fields; contains interlaced frames
-> avg. nom. bitrate 14013653bps (min/max: 13239600/14704000)
-> set first sequence_header bitrate to 9800000bps
===> new File: C:\Capture\test\0817-224536.mpv

--> AC-3/DTS Audio on PID 0x24
Audio PTS: first packet 08:57:33.552, last packet 08:57:46.032
Video PTS: start 1.GOP 08:57:34.349, end last GOP 08:57:46.595
-> adjusting audio at video-timeline
!> missing syncword @ 0, @ 00:00:00.000
!> found syncword @ 304
=> src_audio: AC-3, CM, 2/0(2.0), 48000Hz, 192kbps @ 00:00:00.000
-> 11 frame(s) (352ms) added @ 00:00:11.904
audio frames: wri/pre/skip/ins/add 383/0/0/0/11 @ 00:00:12.256 done..
===> new File: C:\Capture\test\0817-224536.ac3

--> AC-3/DTS Audio on PID 0x25
Audio PTS: first packet 08:57:33.591, last packet 08:57:46.071
Video PTS: start 1.GOP 08:57:34.349, end last GOP 08:57:46.595
-> adjusting audio at video-timeline
!> missing syncword @ 0, @ 00:00:00.000
!> found syncword @ 576
=> src_audio: AC-3, CM, 1/0(1.0), 48000Hz, 192kbps @ 00:00:00.000
-> 11 frame(s) (352ms) added @ 00:00:11.904
audio frames: wri/pre/skip/ins/add 383/0/0/0/11 @ 00:00:12.256 done..
===> new File: C:\Capture\test\0817-224536_1.ac3

summary of created media files:
.Video (m2v): 367 Frames 00:00:12.240 C:\Capture\test\0817-224536.mpv
Audio 0 (ac3): 383 Frames 00:00:12.256 0/0/0/11 C:\Capture\test\0817-224536.ac3
Audio 1 (ac3): 383 Frames 00:00:12.256 0/0/0/11 C:\Capture\test\0817-224536_1.ac3
=> 22037936 bytes written...

[WannaB]

If anyone is interested, the problem has been magically resolved. Again, nothing has changed on my end but now everything is fine. I haven't been able to speak to the station engineer, but the only explanation I can come up with is that the problem was on their end. If that's correct, I'm surprised it took them several days to fix it. Maybe very few people actually watch the digital feeds of their local programming so mine was the only complaint/inquiry? I'm still curious as to why it didn't affect any of their network programming.

Anyway, thanks for the input.