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| Bad stream diagnosed: UK DVB-T -> DVD. Was I just unluck http://forums.linhes.org/viewtopic.php?f=17&t=14184 |
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| Author: | Steve Hosgood [ Thu Feb 15, 2007 4:11 am ] |
| Post subject: | Bad stream diagnosed: UK DVB-T -> DVD. Was I just unluck |
I captured a transport stream (TS) from BBC2 and used "mythtranscode --mpeg2" to convert to programme stream (PS). Then I tried to build a DVD from it using 'dvdstyler' (a really great program BTW). Failure. The video stream within the multiplex wasn't recognised. Hmm - I already knew that the PS itself played just fine on 'mplayer'. So I tried 'xine' and it played just fine there too. I used the '-dumpvideo' option of 'mplayer' to extract the video elemental stream from the PS for a closer look. Playing it on 'mplayer' still worked, but 'file' didn't recognise it as an MPEG video stream. So I took a really close look with 'od -tx1' and found that it *was* a valid video stream, but just with a single stray null byte on the front. Removed that (with 'dd' - took ages, there must have been a better way) and now 'file' recognised it for what it was. I re-multiplexed this repaired video stream together with its audio into a fresh PS file and tried *that* with 'dvdstyler' and it worked fine this time. SO - what the ***** happened there? I was inclined to blame 'mythtranscode' initially, until I realise that mythtranscode had correctly extracted the PS from the TS and could hardly be expected to have looked inside the PS to spot a broken elemental stream (or should it have done that?). After all, the PS itself was correct and demultiplexed correctly. So where did the stray single null come from? Unfortunate transmission error? I've converted a lot of programmes off TV into DVDs and I've never seen this before. I suppose what I need to know here is: does an MPEG TS encapsulate an MPEG PS or are they unrelated container formats for elemental streams? If they are unrelated, then this could be down to 'mythtranscode' after all, but if not then I'm at a loss to explain it. Steve |
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