readme

网络MPEG4IP流媒体开发源代码

July 29, 2002 - Dave Mackie

MP4LIVE 
=======

MP4LIVE is a Linux audio/video capture utility that can capture and encode 
audio and video in real-time. The results can be written to either an .mp4
file, transmitted onto the network via either unicast or multicast, or both 
simultaneously! The audio is encoded with MP3 or AAC, and the video with 
MPEG-4 Simple Profile.

Please use the MPEG4IP SourceForge site to report problems, suggest 
enhancements, ask questions, etc. The URL is 
http://www.sourceforge.net/projects/mpeg4ip

Changes in Version 0.9.8
========================
Major syncronization changes.

Changes in Version 0.9.7
========================

Split out encoder specific information from the base architecture
(rtp transmitter, file recorder).  This enables easy addition of 
codecs.

Reworked configuration variables.


Changes in Version 0.9.5
========================

Once again, fixes for A/V sync and adapting to encoding speed.

Added UI to easily load and save configuration files

SDP now reflects media bandwidth

Experimental file sources is removed.


Hardware Requirements
=====================
Pentium III class machine of at least 500 MHz 
(Pentium IV class machine at 2 GHz is very nice.)

Note systems vary quite a bit in their video capture abilities. For instance,
I have a name brand 750 MHz PIII that drops frames when pushed to CIF sizes
at greater than 15 fps, but I have a no-name clone with a 800 MHz PIII that 
can encode CIF @ 24 fps no problem.

RAM is not typically an issue. I develop on machines with 128 MB, but I believe much smaller configurations would work fine. The real issue is CPU speed.

A sound card with an OSS compatible driver and capture ability.

A video device with a video4linux (v4l) compatible driver and memory mapped 
capture ability.

Known to work are:
	Video capture cards based on the Brooktree 8x8 chip
	with an analog A/V source - VCR, DVD, Camcorder, Settop box, Tivo, etc.
		Typically a video capture card will support composite video inputs.
		Some will also have S-Video input.
		Others will also have a TV Tuner input.

	Logitech Quickcam Express Webcam

Note on multi-processor machines (SMP): mp4live is multithreaded at a coarse
level. Specifically the video encoder, audio encoder, file recorder, network
transmitter, and user interface each have their own thread. Unfortunately for
owners of multiprocessor machines, the video encoder thread dominates the 
computational requirements so one CPU will be very busy, and the others will
be lightly to moderately loaded. For those looking for a project, a multi-
threaded video encoder would certainly provide an interesting challenge.


Software Requirements
=====================
Linux with a 2.4 or later kernel
	(My development was done on RedHat 7.X)

Drivers for sound and video devices

	bttv 0.7 or later video capture driver
		(Included with RedHat 7.1 and later)
	qce webcam driver


WARNINGS!
=========

Please see the MPEG4IP README regarding legal issues, and the list of 
open source packages that are redistributed with this code.

This is a LINUX program! Do not even think about trying to get this to 
run on Windows! Even moving it to other UNIX systems would require some 
re-programming since the sound and video capture interfaces are Linux 
specific.

By far the easiest route is to use a Linux distribution that already has a
2.4 kernel, the bttv driver, and the associated i2c module built into it.
I've hacked kernels before, and I'm not sure I could sucessfully follow the 
instructions in the bttv driver as to how to configure a kernel so that it 
would work. Caveat emptor!

I've had many headaches with sound cards under Linux. Before you start using 
mp4live, please make sure you're able to playback and record with your sound 
card!

You should definitely increase the number of capture buffers for the bttv 
driver. This reduces the chance of dropping video frames due to transient
delays in the system. By default bttv uses 2 buffers. You can increase this 
by editting /etc/modules.conf and adding the line 
"add options bttv gbuffers=32"
at the end of the file. The value 32 is my recommendation but you can 
experiment with other values if you are so inclined.


Tips
====

I suggest you disable any fancy, computationally intensive screensavers 
when using mp4live to capture long programs. Along the same lines, don't
run any programs that make large resource demands (CPU, bus, disk, network)
while mp4live is running.

If you're capturing large video image sizes, then you may be able to boost
the encoded video frame rate by disabling video preview.  In general, once
you've got the system working, disabling preview is a good idea.

The AAC audio encoder is noticeably slower than the MP3 audio encoder so 
you will see lower video frame rates and greater sensitivity to CPU load 
if you are using AAC.

Linux supports the POSIX soft real-time extensions and mp4live will attempt
to use these to give it priority over non-real time processes. Typically
these calls can only be made by processes with root privileges, so you may
want to run mp4live as root for this reason.

If you have the latest version of OSS, you have a chance of detecting
audio overruns.  That, in combination with the latest version and
working on a fast machine will give fairly good lip syncronization up to
about the hour mark running 90% of the CPU.

Building and Installing
=======================

See the MPEG4IP README for general notes about the build environment. 

Assuming you've already done a build at the top level of mpeg4ip, and
you're on a Linux system then mp4live should be built and waiting for you
in this directory. If you've done a top level 'make install', the mp4live
will be installed into '/usr/local/bin'. Of course, you can also issue 
'make' and 'make install' from this directory as well.


Using mp4live
=============

Typically, there is no need for command line options to mp4live. You can
just type 'mp4live' and you'll be up and running.

If you change an mp4live configuration setting, then that change will be 
saved in your home directory in ~/.mp4live_rc. This file is read when 
mp4live is started, and the configuration settings adjusted accordingly.

The default settings for mp4live are to record 1 minute of audio and video
to an mp4 file, ./capture.mp4  The first time you use the program, it's
a good idea to just hit the Start button, and see what happens. If all
goes well, 1 minute later you have a playable/streamable mp4 file. If you
don't get this, then it's time to review this README, and it that doesn't
help, then fire off a message on the MPEG4IP SourceForge discussion group.

Assuming things are working you can now use the Settings buttons to adjust
things like the video size and frame rate, the audio sampling rate, the 
encoded bitrates, etc. The UI is hopefully self-explanatory. If not, let us
know what's confusing and we'll look at fixing that. (I'm a big believer that
if you need to read a document to use a UI, then the UI is broken and should
be fixed. Of course, as I've re-learned many times, what is obvious and natural
to me, isn't always to other people.)

If you're capturing video that uses "widescreen" or "letterbox" format, 
it's a big win to change the "Aspect Ratio" in the Video Settings. This 
will cause the video to be automatically cropped so you don't waste precious 
CPU time encoding the empty black bars at the top and bottom of the screen. 

The capture cards will always try to capture frame rates based on what
the setting of the video card is (either NTSC or PAL).

The default is to assume that the video driver is going to capture close
to the correct frame rate of 29.97 for NTSC, 25 for PAL.  If you don't 
think that this is working quite right, try the "videoTimestampCache=0"
to the .mp4live_rc before you start.  (This may be the case with usb