Posted: Tue May 16, 2006 10:28 pm Post subject: [Asterisk-video] RE: Video transcoding
17 maj 2006 kl. 09.25 skrev Sergio Garc?a Murillo:
Quote:
And regarding video transcoding, it would be great to have some
capabilities integrated within asterisk so we could use the error
correction mechanism defined in AL3 to provide a much better video
quality.
Does asterisk offer any capability? How it's handled in audio? Any
possibility of integrating libavocdec/ffmpeg or similar library?
My question is this:
- Is it realistic to do video transcoding on the platforms we run
Asterisk on? How many channels?
- Would a graphics card, like the Hauppage with mpeg chips on it, help?
Posted: Tue May 16, 2006 10:46 pm Post subject: [Asterisk-video] RE: Video transcoding
Quote:
My question is this:
- Is it realistic to do video transcoding on the platforms we run
Asterisk on? How many channels?
I have been running ffmpeg/libavcodec h263 in a videoconference client in a 300 Mhz geode cpu, and over 10 simultaneous encoding/decoding in a P4 3GHZ with not much load (I don't remember the figures).
It also depends on the fps and size of the video been encoded/decoded, for an H324M it would be easy.. :)
Probably transcoding many h264s at high rates it's not possible, but running a big number of h261/h263 is.
Another question is if it's really needed or not..
Quote:
- Would a graphics card, like the Hauppage with mpeg chips on it,
I see it much more useful an array of dsp on a pci card or similar. Perhaps it's a good idea to make it open so new implementations could be added in the future..
Greetings
Sergio
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Posted: Tue May 16, 2006 10:54 pm Post subject: [Asterisk-video] RE: Video transcoding
Quote:
for an H324M it would be easy.. :) Probably transcoding
many h264s at high rates it's not possible, but running a
big number of h261/h263 is. Another question is if it's
really needed or not..
I would be using that function a lot, because I'm connecting
quite a few users whi's willing to be transcoded in case of
Videocall.
Posted: Tue May 16, 2006 11:00 pm Post subject: [Asterisk-video] RE: Video transcoding
Hi Olle, Sergio,
It depends on how you do you're transcoding. The decoding is simple(ish) enough, it's the encoding that takes the time (in the order of 10 times longer to encode than decode). And what really takes the time with encoding is doing the video pre-filtering and motion estimation. When you're transcoding you can get away with almost none of these complex processes (though H.264 complicates things). Because you're doing a decode followed by an encode you can use the decoded motion vectors as input to the encoder - they may get scaled down or manipulated but you don't have to do O(N2) calculations to get them.
Certainly a dedicated DSP (like the PixelWorks BSP-15 or TI 6446) would do a nice job of transcoding the video on a PCI card. Perhaps the SIMD pixel engines in a graphics card would be able to do something, but getting the manufacturers to support your code development might be tricky. Even finding register and instruction sets has been tough in the past. The MPEG chips on the graphics cards can be too MPEG and too decode only to do H.26x, but that's changing with the likes of TI and PixelWorks getting to lower cost points.
And to move onto Sergios question on ffmpeg and the like. Those codecs are generally centred around a full decode and encode path. If you wanted a low-cpu usage transcoder then you'd have to break up the codecs and intercept some of the internal data paths. That's possible for sure, but may not get much support from the people maintaining the projects to keep those compilation options bug free... dunno, just my thoughts.
As to whether it's a good idea to do this sort of thing on an Asterisk platform: Trancoders, and their big brother MCUs, cost upwards or $1000 a port (with perhaps 8, 12 or 16 port minimums), there's definitely a market for small low cost units for SME. You'd want to do the transcoding/MCU on a different box so as not to impact the main switch, but there's a demand I think.
-----Original Message-----
From: asterisk-video-bounces@lists.digium.com [mailto:asterisk-video-bounces@lists.digium.com] On Behalf Of Olle E Johansson
Sent: 17 May 2006 08:28
To: Discussion of video media support in Asterisk
Subject: Re: [Asterisk-video] RE: Video transcoding
17 maj 2006 kl. 09.25 skrev Sergio Garc?a Murillo:
Quote:
And regarding video transcoding, it would be great to have some
capabilities integrated within asterisk so we could use the error
correction mechanism defined in AL3 to provide a much better video
quality.
Does asterisk offer any capability? How it's handled in audio? Any
possibility of integrating libavocdec/ffmpeg or similar library?
My question is this:
- Is it realistic to do video transcoding on the platforms we run
Asterisk on? How many channels?
- Would a graphics card, like the Hauppage with mpeg chips on it, help?
/O
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