[mythtv] Live transcode while recording

Chase Douglas chasedouglas.lists at gmail.com
Mon Dec 1 13:57:36 UTC 2008

On Dec 1, 2008, at 3:21 AM, Rob Smith wrote:
> On Sun, Nov 30, 2008 at 9:02 PM, Nigel Pearson  
> <nigel at ind.tansu.com.au> wrote:
>>> the moov atom contains absolute bit offsets for the stream.
>> Do the offsets have to be accurate?
>> If not, a dummy header could be generated
>> with estimates based on recording length,
>> bitrate, et c.
> When I first got my ipod touch, I attempted to do just that and only
> succeeded in crashing it hard. I took a 60 second pre-encoded video
> and also screwed with it's header and it would crash with the header
> offsets being off by one byte. It doesn't seem like the device can
> handle anything but the perfect header.
> It also attempts to do http partial content requests based on the info
> in that header, so seeking would likely be broken if it was succeeded
> in being faked.
> Perhaps someone with more understanding of video can come up with a
> solution, but I'm fairly sure it's not easy to say the least.

There is a new iPhone app named Orb Live that can stream live video  
from an Orb server you set up, just like mythbackend streaming to a  
frontend. An individual
performed a grep of ffmpeg on the Orb Live binary and showed that they  
were indeed using ffmpeg decoding for their streams. With this  
knowledge, I've been working on an iPhone video player myself that  
should handle streams. The ultimate goal is to make an iPhone frontend.

This is all still in the very formative stage, but I hope to have a  
general video player working within a week or two. I currently have  
video playback and need to add audio and buffering for both streams.  
Once something useful results, I will be putting it up at assembla.com  
under the GPLv2.

It remains to be seen how this will affect battery life since only  
Apple has access to the hw decoding capabilities of the iPhone. The  
best I have been able to do with sw decoding is a 256x256 recording  
(scaled to the correct aspect ratio) at 15 fps mpeg2 200 kbps. I think  
that leaves just enough headroom for audio decoding and network  

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