[mythtvnz] Transcoding help?...

[Steven Ellis]

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.

Steve


--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email   - steven at openmedia.co.nz
website - http://www.openmedia.co.nz