162 lines
6.6 KiB
Plaintext
162 lines
6.6 KiB
Plaintext
The FFserver streaming HOWTO
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Philip Gladstone <philip-ffserver@gladstonefamily.net>
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Last updated: July 26, 2002
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0. What is this HOWTO about?
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This covers only the streaming aspects of ffserver / ffmpeg. All questions about
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parameters for ffmpeg, codec questions, etc. are not covered here.
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You should also read the ffserver.txt file in this directory. It contains
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roughly the same information.
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1. What can this do?
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When properly configured and running, you can capture video and audio in real
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time from a suitable capture card, and stream it out over the Internet to
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either Windows Media Player or RealAudio player (with some restrictions).
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It can also stream from files, though that is currently broken. Very often, a
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web server can be used to serve up the files just as well.
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2. What do I need?
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I use Linux on a 900MHz Duron with a cheapo Bt848 based TV capture card. I'm
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using stock linux 2.4.17 with the stock drivers. [Actually that isn't true,
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I needed some special drivers from my motherboard based sound card.]
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I understand that FreeBSD systems work just fine as well.
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3. How do I make it work?
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First, build the kit. It *really* helps to have installed LAME first. Then when
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you run the ffserver ./configure, make sure that you have the --enable-mp3lame
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flag turned on.
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LAME is important as it allows streaming of audio to Windows Media Player. Don't
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ask why the other audio types do not work.
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As a simple test, just run the following two command lines:
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./ffserver -f doc/ffserver.conf &
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./ffmpeg http://localhost:8090/feed1.ffm
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At this point you should be able to go to your windows machine and fire up
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Windows Media Player (WMP). Go to Open URL and enter
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http://<linuxbox>:8090/test.asf
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You should see (after a short delay) video and hear audio.
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WARNING: trying to stream test1.mpg doesn't work with WMP as it tries to
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transfer the entire file before starting to play.
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4. What happens next?
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You should edit the ffserver.conf file to suit your needs (in terms of
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frame rates etc). Then install ffserver and ffmpeg, write a script to start
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them up, and off you go.
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5. Troubleshooting
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* I don't hear any audio, but video is fine
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Maybe you didn't install LAME, or get your ./configure statement right. Check
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the ffmpeg output to see if a line referring to mp3 is present. If not, then
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your configuration was incorrect. If it is, then maybe your wiring is not
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setup correctly. Maybe the sound card is not getting data from the right
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input source. Maybe you have a really awful audio interface (like I do)
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that only captures in stereo and also requires that one channel be flipped.
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If you are one of these people, then export 'AUDIO_FLIP_LEFT=1' before
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starting ffmpeg.
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* The audio and video loose sync after a while.
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Yes, they do.
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* After a long while, the video update rate goes way down in WMP.
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Yes, it does. Who knows why?
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* WMP 6.4 behaves differently to WMP 7.
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Yes, it does. Any thoughts on this would be gratefully received. These
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differences extend to embedding WMP into a web page. [There are two
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different object ids that you can use, one of them -- the old one -- cannot
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play very well, and the new one works well (both on the same system). However,
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I suspect that the new one is not available unless you have installed WMP 7].
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6. What else can it do?
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There seems to be a bunch of code that allows you to replay previous
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video. I've never tried it, so it probably doesn't work properly. YMMV.
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In fact, in order to get some level of stability, ffserver now deletes
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all the previously sent video whenever it restarts.
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You can fiddle with many of the codec choices and encoding parameters, and
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there are a bunch more parameters that you cannot control. Post a message
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to the mailing list if there are some 'must have' parameters. Look in the
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ffserver.conf for a list of the currently available controls.
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It will automatically generate the .ASX or .RAM files that are often used
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in browsers. These files are actually redirections to the underlying .ASF
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or .RM file. The reason for this is that the browser often fetches the
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entire file before starting up the external viewer. The redirection files
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are very small and can be transferred quickly. [The stream itself is
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often 'infinite' and thus the browser tries to download it and never
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finishes.]
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7. Tips
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* When you connect to a live stream, most players (WMP, RA etc) want to
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buffer a certain number of seconds of material so that they can display the
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signal continuously. However, ffserver (by default) starts sending data
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in real time. This means that there is a pause of a few seconds while the
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buffering is being done by the player. The good news is that this can be
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cured by adding a '?buffer=5' to the end of the URL. This says that the
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stream should start 5 seconds in the past -- and so the first 5 seconds
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of the stream is sent as fast as the network will allow. It will then
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slow down to real time. This noticeably improves the startup experience.
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You can also add a 'Preroll 15' statement into the ffserver.conf that will
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add the 15 second prebuffering on all requests that do not otherwise
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specify a time. In addition, ffserver will skip frames until a key_frame
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is found. This further reduces the startup delay by not transferring data
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that will be discarded.
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* You may want to adjust the MaxBandwidth in the ffserver.conf to limit
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the amount of bandwidth consumed by live streams.
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8. Why does the ?buffer / Preroll stop working after a time?
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It turns out that (on my machine at least) the number of frames successfully
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grabbed is marginally less than the number that ought to be grabbed. This
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means that the timestamp in the encoded data stream gets behind real time.
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This means that if you say 'preroll 10', then when the stream gets 10
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or more seconds behind, there is no preroll left.
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Fixing this requires a require in the internals in how timestampts are
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handled.
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9. Does the ?date= stuff work.
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Yes (subject to the caution above). Also note that whenever you start
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ffserver, it deletes the ffm file, thus wiping out what you had recorded
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before. This behaviour is a temporary fix to various crashes. The aim is
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to fix it so that the old data is saved if possible.
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The format of the ?date=xxxxxx is fairly flexible. You should use one
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of the following formats (the 'T' is literal):
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* YYYY-MM-DDTHH:MM:SS (localtime)
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* YYYY-MM-DDTHH:MM:SSZ (UTC)
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You can omit the YYYY-MM-DD, and then it refers to the current day. However
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note that ?date=16:00:00 refers to 4PM on the current day -- this may be
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in the future and so unlikely to useful.
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You use this by adding the ?date= to the end of the URL for the stream.
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For example: http://localhost:8080/test.asf?date=2002-07-26T23:05:00
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