[mythtvnz] Transcoding help?...

[Stephen Worthington]

On Wed, 12 Aug 2009 07:38:01 +1200, you wrote:

>On Mon, 10 Aug 2009 23:36, Ross and Jemima Knudsen wrote:
>> Hi Tony,
>>
>> Thanks for your response.  I didn't think that mythtranscode worked at
>> all.  Everything I read seemed to indicate it can't handle h264 content.
>
>I have found this write-up that has been helping me understand h264 in ffmpeg
>
>     http://rob.opendot.cl/index.php/useful-stuff/ffmpeg-x264-encoding-guide/
>
>h264 encoding is slow though I get about 3 fps on my 3GHz 1GB Ram P4!
>
>> I can definitely relate to the audio sync issues.  Its hard to tell but
>> I think the sync gets worse the longer it plays.  
>
>Yes I noticed that too.
>
>I have found that if you use mythtranscode the sound sems to stay in sync
> very nicely ... the downside being that there are fewer knobs to "twiddle"
> and you get a nuv file that might have to be processed again to get to a
> more standard container format.  Also as I pointed out it seems to be
> "flakey" at the moment with approx 5% of my transcodes failing .
>
>> I tried a number of
>> different options based on what you suggested for a "lossless"
>> transcode.  I got the following output:
>>
>> http://openwrt.pastebay.org/pastebay.php?dl=39551
>>
>> What I think is interesting is that video output is not quite identical
>> to the input even though its supposed to be copying the stream.  Also
>> I'm assuming that the reference frame errors, unref short failure and
>> missing picture errors are ok and not causing my problems...
>
>I get the same sorts of errors  sometimes many sometimes few ... I just
>presumed that they were transmission errors on the broadcast stream (there is
>no error correction like in a TCP/IP stream).
>They seem to do no harm although I do sometimes see some artifacts that only
>last a frame or two.

I thought that one of the differences between a "program stream"
container (such as the usual .mpg file) and a "transport stream" (.ts
container) was the ability to transmit redundant error correction
data.  Maybe DVB in NZ is not actually transmitted with error
correction, but I would have thought that would be pretty silly.  Does
anyone know how to find out if the transmitted streams contain error
correction, and if so how much is transmitted?  I know that I get
occasional errors in my DVB-T programs, and other people report the
same, so clearly insufficient error correction is being done.

  http://en.wikipedia.org/wiki/MPEG_transport_stream