FFserver Documentation: 1. Introduction

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# 1. Introduction

FFserver is a streaming server for both audio and video. It supports several live feeds, streaming from files and time shifting on live feeds (you can seek to positions in the past on each live feed, provided you specify a big enough feed storage in ffserver.conf).

This documentation covers only the streaming aspects of ffserver / ffmpeg. All questions about parameters for ffmpeg, codec questions, etc. are not covered here. Read ``ffmpeg-doc.html'` for more information.

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# 2. QuickStart

[Contributed by Philip Gladstone, philip-ffserver at gladstonefamily dot net]

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## 2.1 What can this do?

When properly configured and running, you can capture video and audio in real time from a suitable capture card, and stream it out over the Internet to either Windows Media Player or RealAudio player (with some restrictions).

It can also stream from files, though that is currently broken. Very often, a web server can be used to serve up the files just as well.

It can stream prerecorded video from .ffm files, though it is somewhat tricky to make it work correctly.

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## 2.2 What do I need?

I use Linux on a 900MHz Duron with a cheapo Bt848 based TV capture card. I'm using stock Linux 2.4.17 with the stock drivers. [Actually that isn't true, I needed some special drivers for my motherboard-based sound card.]

I understand that FreeBSD systems work just fine as well.

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## 2.3 How do I make it work?

First, build the kit. It *really* helps to have installed LAME first. Then when you run the ffserver ./configure, make sure that you have the `--enable-libmp3lame` flag turned on.

LAME is important as it allows for streaming audio to Windows Media Player. Don't ask why the other audio types do not work.

As a simple test, just run the following two command lines (assuming that you have a V4L video capture card):

    ./ffserver -f doc/ffserver.conf &
    ./ffmpeg http://localhost:8090/feed1.ffm

At this point you should be able to go to your Windows machine and fire up Windows Media Player (WMP). Go to Open URL and enter

        http://<linuxbox>:8090/test.asf

You should (after a short delay) see video and hear audio.

WARNING: trying to stream test1.mpg doesn't work with WMP as it tries to transfer the entire file before starting to play. The same is true of AVI files.

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## 2.4 What happens next?

You should edit the ffserver.conf file to suit your needs (in terms of frame rates etc). Then install ffserver and ffmpeg, write a script to start them up, and off you go.

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## 2.5 Troubleshooting

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### 2.5.1 I don't hear any audio, but video is fine.

Maybe you didn't install LAME, or got your ./configure statement wrong. Check the ffmpeg output to see if a line referring to MP3 is present. If not, then your configuration was incorrect. If it is, then maybe your wiring is not set up correctly. Maybe the sound card is not getting data from the right input source. Maybe you have a really awful audio interface (like I do) that only captures in stereo and also requires that one channel be flipped. If you are one of these people, then export 'AUDIO_FLIP_LEFT=1' before starting ffmpeg.

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### 2.5.2 The audio and video loose sync after a while.

Yes, they do.

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### 2.5.3 After a long while, the video update rate goes way down in WMP.

Yes, it does. Who knows why?

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### 2.5.4 WMP 6.4 behaves differently to WMP 7.

Yes, it does. Any thoughts on this would be gratefully received. These differences extend to embedding WMP into a web page. [There are two object IDs that you can use: The old one, which does not play well, and the new one, which does (both tested on the same system). However, I suspect that the new one is not available unless you have installed WMP 7].

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## 2.6 What else can it do?

You can replay video from .ffm files that was recorded earlier. However, there are a number of caveats, including the fact that the ffserver parameters must match the original parameters used to record the file. If they do not, then ffserver deletes the file before recording into it. (Now that I write this, it seems broken).

You can fiddle with many of the codec choices and encoding parameters, and there are a bunch more parameters that you cannot control. Post a message to the mailing list if there are some 'must have' parameters. Look in ffserver.conf for a list of the currently available controls.

It will automatically generate the ASX or RAM files that are often used in browsers. These files are actually redirections to the underlying ASF or RM file. The reason for this is that the browser often fetches the entire file before starting up the external viewer. The redirection files are very small and can be transferred quickly. [The stream itself is often 'infinite' and thus the browser tries to download it and never finishes.]

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## 2.7 Tips

* When you connect to a live stream, most players (WMP, RA, etc) want to buffer a certain number of seconds of material so that they can display the signal continuously. However, ffserver (by default) starts sending data in realtime. This means that there is a pause of a few seconds while the buffering is being done by the player. The good news is that this can be cured by adding a '?buffer=5' to the end of the URL. This means that the stream should start 5 seconds in the past - and so the first 5 seconds of the stream are sent as fast as the network will allow. It will then slow down to real time. This noticeably improves the startup experience.

You can also add a 'Preroll 15' statement into the ffserver.conf that will add the 15 second prebuffering on all requests that do not otherwise specify a time. In addition, ffserver will skip frames until a key_frame is found. This further reduces the startup delay by not transferring data that will be discarded.

* You may want to adjust the MaxBandwidth in the ffserver.conf to limit the amount of bandwidth consumed by live streams.

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## 2.8 Why does the ?buffer / Preroll stop working after a time?

It turns out that (on my machine at least) the number of frames successfully grabbed is marginally less than the number that ought to be grabbed. This means that the timestamp in the encoded data stream gets behind realtime. This means that if you say 'Preroll 10', then when the stream gets 10 or more seconds behind, there is no Preroll left.

Fixing this requires a change in the internals of how timestamps are handled.

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## 2.9 Does the `?date=` stuff work.

Yes (subject to the limitation outlined above). Also note that whenever you start ffserver, it deletes the ffm file (if any parameters have changed), thus wiping out what you had recorded before.

The format of the `?date=xxxxxx` is fairly flexible. You should use one of the following formats (the 'T' is literal):

    * YYYY-MM-DDTHH:MM:SS     (localtime)
    * YYYY-MM-DDTHH:MM:SSZ    (UTC)

You can omit the YYYY-MM-DD, and then it refers to the current day. However note that ``?date=16:00:00'` refers to 16:00 on the current day - this may be in the future and so is unlikely to be useful.

You use this by adding the ?date= to the end of the URL for the stream. For example: ``http://localhost:8080/test.asf?date=2002-07-26T23:05:00'`.

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# 3. Invocation

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## 3.1 Syntax

    ffserver [options]

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## 3.2 Options

``-L'`

  Print the license.

``-h'`

  Print the help.

``-f configfile'`

  Use ``configfile'` instead of ``/etc/ffserver.conf'`.

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