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Re[2]: [Gnash-dev] Video streaming: manually specify codec

From: Udo Giacomozzi
Subject: Re[2]: [Gnash-dev] Video streaming: manually specify codec
Date: Thu, 2 Jul 2009 16:25:34 +0200

Hello strk,

Tuesday, June 30, 2009, 11:04:39 PM, you wrote:
s> You're talking about "format" here, not codec, right ?

Don't know if "mjpeg" classifies as a format or a codec. It's
basically one still JPEG image after another in a stream, separated
using MIME boundaries just like in a multipart e-mail.

The web server serving this stream just tells the client that it will
send "mixed/multipart" data. Maybe each "part" of the stream will have
it's own content-type, but I don't know that.

s> I'm not a media expert, but I've seen at least ffmpeg threating
s> formats differently from codecs.

Is "format" a synonym for "container" ?

s> For formats, AS doesn't let you specify anything because it only
s> supports FLV. Or am I missing something ?

Not true, you can easily show MPEG streams not embedded in a FLV
container using NetStream:

---- AS CODE -----------------------------------------------------
url = /* any URL to a .MPG file or similar */;

var connection_nc:NetConnection = new NetConnection();
var stream_ns:NetStream = new NetStream(connection_nc);
---- AS CODE -----------------------------------------------------

In the case of a .mpg file, Gnash/Ffmpeg will correctly detect the
container/format/codec. I guess this applies to a lot more formats.

The same happens when using the "ffmpeg" command line tool...

ffmpeg -i test.avi

But reading from a IP camera requires an extra parameter:

ffmpeg -f mjpeg -i http://camera/stream.jpg test.avi

s> We had a discussion about how to support different formats
s> in the past, but that discussion didn't result in any implementation.
s> The summary should be here:

That seems to talk about detecting available codecs. My case is
different in that I know that ffmpeg has all necessary plugins
installed but ffmpeg itselfs apparently has no way to detect the
required plugin (unless I manually specify it, which works very well).

s> Shouldnt' av_find_input_format() find out autonomously the actual
s> format by looking at magic numebrs or similar ? Have you asked
s> the ffmpeg developers about it ? Maybe we're just not providing
s> enough "probe" bytes ?

Probably there is simply no auto-detection for mjpeg available (or why
would the command line tool fail?).


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