[mythtvnz] Transcoding help?...

[Nick Rout]

On Wed, Aug 12, 2009 at 4:01 PM, Steven Ellis<steven at openmedia.co.nz> wrote:
>
> On Wed, August 12, 2009 12:58 pm, Stephen Worthington wrote:
>> 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
>
> Sadly ProjectX doesn't support H264 video streams as it does a great job
> dealing with errors in MPEG2 based TS streams.
>
> TS has been designed to elegantly deal with the occasional transmission
> error, but these errors will cause issues if you are transcoding to
> another format.
>
> Sadly I don't know of an equivalent H.264 ready tool.

I think dvbcut may be working on it, but last time I looked it wasn't
exactly a 'hold your breath' scenario.