Mailing List Archive: MythTV: Dev

mythcommflag gets mpeg2video errors not seen in playback

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km at mathcs

Sep 3, 2007, 8:42 AM

Post #1 of 2 (720 views)
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mythcommflag gets mpeg2video errors not seen in playback

mythcommflag gives a large number of

[mpeg2video @ 0xb73ddb68]current_picture not initalized
2007-09-03 11:09:32.693 AFD Error: Unknown decoding error

on firewire streams captured on a comcast cable box. The commerical
marking on these streams are very unreliable, clearly the time offsets
generated are out of sync with the video playback. These particular
streams are from extended basic sd digital channels (fx,usa, comedy
central, ..) which are encrypted. However, the firewire captured mpeg
transport streams play perfectly well in myth. OTA streams captured in
the same way don't seem to have this problem.

My thought is that mythcommflag is not using the same codec as the myth
native player. Here is some comparative output

From mythfrontend

2007-09-03 11:19:50.195 AFD: Stream #0, has id 0x2240 codec id
MPEG2VIDEO, type Video, bitrate 15000000 at 0x0x884a910
2007-09-03 11:19:50.196 detectInterlace(Detect Scan, Interlaced Scan,
29.97, 480) ->Interlaced Scan
2007-09-03 11:19:50.196 AFD: Looking for decoder for MPEG2VIDEO
2007-09-03 11:19:50.196 AFD: Opened codec 0x8b24860, id(MPEG2VIDEO)
type(Video)

From mythcommflag
2007-09-03 11:09:32.035 AFD: Stream #0, has id 0x2240 codec id
MPEG2VIDEO, type Video, bitrate 15000000 at 0x0x81ff890
2007-09-03 11:09:32.037 detectInterlace(Detect Scan, Interlaced Scan,
29.97, 480) ->Interlaced Scan
2007-09-03 11:09:32.037 AFD: Looking for decoder for MPEG2VIDEO
2007-09-03 11:09:32.037 AFD: Opened codec 0x81ff990, id(MPEG2VIDEO)
type(Video)

What strikes me is that mythfrontend sees 0x0x884a910 and opens codec
0x8b24860.

mythcommflag sees 0x0x81ff890 and opens codec 0x81ff990.

I have to admit I don't understand the hex values. Are they just memory
addresses where the codecs are loaded, or are they absolute id numbers?

Is it significant that mythfrontend has two different hex values, and
mythcommflag has the same on detect and open?

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km at mathcs

Sep 8, 2007, 5:31 PM

Post #2 of 2 (611 views)
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Re: mythcommflag gets mpeg2video errors not seen in playback [In reply to]

Previously I posted:

> mythcommflag gives a large number of
> [mpeg2video @ 0xb73ddb68]current_picture not initalized
> 2007-09-03 11:09:32.693 AFD Error: Unknown decoding error
>
> on firewire streams captured on a comcast cable box. The commerical
> marking on these streams are very unreliable, clearly the time offsets
> generated are out of sync with the video playback. These particular
> streams are from extended basic sd digital channels (fx,usa, comedy
> central, ..) which are encrypted. However, the firewire captured mpeg
> transport streams play perfectly well in myth.

At that time I thought the problem was that mythcommflag may have been
using a different codec then mythfrontend. Thats not the case, they are
using exactly the same mpeg_decode_frame in mpeg12.c.

After some debugging the real problem boils down to this. The errors
don't show when playing the streams because they are played
sequentially. mythcommflag seeks forward skipping frames incorrectly for
these streams and then tries to decode garbage. Eventually it recovers
but the indexing is then off.

I need someone more expert than me to help look at a sample stream and
help pin down the error. I have a 1MB stream that illustrates the
problem. mythcommflag tries to skip from frame 30 to frame 58 and thats
where the problem occurs. mpeg_decode_frame is called 5 times
successfully, the 6th time follows a AvFormatDecoder::SeekReset which
attempts to skip 28 frames, and this one is given garbage.

I submitted this as ticket number 3925. I would like to have attached my
1MB sample but that exceeds the 256K limit, but I can provide it to
anyone who wants to take a look. Alternately if you can suggest a
diagnostic tool to analyze the 58 frames to define the issue that would
be helpful.

I don't think this is an isolated error or anything to do with
corruption. I see this consistently on streams from certain digital
channels.
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