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1The FFserver streaming HOWTO
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3
4Philip Gladstone <philip-ffserver@gladstonefamily.net>
ce838977 5Last updated: July 26, 2002
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70. What is this HOWTO about?
8
9This covers only the streaming aspects of ffserver / ffmpeg. All questions about
10parameters for ffmpeg, codec questions, etc. are not covered here.
11
12You should also read the ffserver.txt file in this directory. It contains
13roughly the same information.
14
151. What can this do?
16
17When properly configured and running, you can capture video and audio in real
18time from a suitable capture card, and stream it out over the Internet to
19either Windows Media Player or RealAudio player (with some restrictions).
20
21It can also stream from files, though that is currently broken. Very often, a
22web server can be used to serve up the files just as well.
23
242. What do I need?
25
26I use Linux on a 900MHz Duron with a cheapo Bt848 based TV capture card. I'm
27using stock linux 2.4.17 with the stock drivers. [Actually that isn't true,
28I needed some special drivers from my motherboard based sound card.]
29
30I understand that FreeBSD systems work just fine as well.
31
323. How do I make it work?
33
34First, build the kit. It *really* helps to have installed LAME first. Then when
35you run the ffserver ./configure, make sure that you have the --enable-mp3lame
36flag turned on.
37
38LAME is important as it allows streaming of audio to Windows Media Player. Don't
39ask why the other audio types do not work.
40
41As a simple test, just run the following two command lines:
42
43./ffserver -f doc/ffserver.conf &
44./ffmpeg http://localhost:8090/feed1.ffm
45
46At this point you should be able to go to your windows machine and fire up
47Windows Media Player (WMP). Go to Open URL and enter
48
49 http://<linuxbox>:8090/test.asf
50
51You should see (after a short delay) video and hear audio.
52
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53WARNING: trying to stream test1.mpg doesn't work with WMP as it tries to
54transfer the entire file before starting to play.
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564. What happens next?
57
58You should edit the ffserver.conf file to suit your needs (in terms of
59frame rates etc). Then install ffserver and ffmpeg, write a script to start
60them up, and off you go.
61
625. Troubleshooting
63
64* I don't hear any audio, but video is fine
65
66Maybe you didn't install LAME, or get your ./configure statement right. Check
67the ffmpeg output to see if a line referring to mp3 is present. If not, then
68your configuration was incorrect. If it is, then maybe your wiring is not
69setup correctly. Maybe the sound card is not getting data from the right
70input source. Maybe you have a really awful audio interface (like I do)
71that only captures in stereo and also requires that one channel be flipped.
72If you are one of these people, then export 'AUDIO_FLIP_LEFT=1' before
73starting ffmpeg.
74
75* The audio and video loose sync after a while.
76
77Yes, they do.
78
79* After a long while, the video update rate goes way down in WMP.
80
81Yes, it does. Who knows why?
82
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83* WMP 6.4 behaves differently to WMP 7.
84
85Yes, it does. Any thoughts on this would be gratefully received. These
86differences extend to embedding WMP into a web page. [There are two
87different object ids that you can use, one of them -- the old one -- cannot
88play very well, and the new one works well (both on the same system). However,
89I suspect that the new one is not available unless you have installed WMP 7].
90
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916. What else can it do?
92
93There seems to be a bunch of code that allows you to replay previous
94video. I've never tried it, so it probably doesn't work properly. YMMV.
95In fact, in order to get some level of stability, ffserver now deletes
96all the previously sent video whenever it restarts.
97
98You can fiddle with many of the codec choices and encoding parameters, and
99there are a bunch more parameters that you cannot control. Post a message
100to the mailing list if there are some 'must have' parameters. Look in the
101ffserver.conf for a list of the currently available controls.
102
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103It will automatically generate the .ASX or .RAM files that are often used
104in browsers. These files are actually redirections to the underlying .ASF
105or .RM file. The reason for this is that the browser often fetches the
106entire file before starting up the external viewer. The redirection files
107are very small and can be transferred quickly. [The stream itself is
108often 'infinite' and thus the browser tries to download it and never
109finishes.]
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1117. Tips
112
113* When you connect to a live stream, most players (WMP, RA etc) want to
114buffer a certain number of seconds of material so that they can display the
115signal continuously. However, ffserver (by default) starts sending data
116in real time. This means that there is a pause of a few seconds while the
117buffering is being done by the player. The good news is that this can be
118cured by adding a '?buffer=5' to the end of the URL. This says that the
119stream should start 5 seconds in the past -- and so the first 5 seconds
120of the stream is sent as fast as the network will allow. It will then
121slow down to real time. This noticeably improves the startup experience.
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122
123You can also add a 'Preroll 15' statement into the ffserver.conf that will
124add the 15 second prebuffering on all requests that do not otherwise
125specify a time. In addition, ffserver will skip frames until a key_frame
126is found. This further reduces the startup delay by not transferring data
127that will be discarded.
128
129* You may want to adjust the MaxBandwidth in the ffserver.conf to limit
130the amount of bandwidth consumed by live streams.
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131
1328. Why does the ?buffer / Preroll stop working after a time?
133
134It turns out that (on my machine at least) the number of frames successfully
135grabbed is marginally less than the number that ought to be grabbed. This
136means that the timestamp in the encoded data stream gets behind real time.
137This means that if you say 'preroll 10', then when the stream gets 10
138or more seconds behind, there is no preroll left.
139
140Fixing this requires a require in the internals in how timestampts are
141handled.
142
1439. Does the ?date= stuff work.
144
145Yes (subject to the caution above). Also note that whenever you start
146ffserver, it deletes the ffm file, thus wiping out what you had recorded
147before. This behaviour is a temporary fix to various crashes. The aim is
148to fix it so that the old data is saved if possible.
149
150The format of the ?date=xxxxxx is fairly flexible. You should use one
151of the following formats (the 'T' is literal):
152
153* YYYY-MM-DDTHH:MM:SS (localtime)
154* YYYY-MM-DDTHH:MM:SSZ (UTC)
155
156You can omit the YYYY-MM-DD, and then it refers to the current day. However
157note that ?date=16:00:00 refers to 4PM on the current day -- this may be
158in the future and so unlikely to useful.
159
160You use this by adding the ?date= to the end of the URL for the stream.
161For example: http://localhost:8080/test.asf?date=2002-07-26T23:05:00