The FFserver streaming HOWTO ---------------------------- Philip Gladstone Last updated: May 16, 2002 0. What is this HOWTO about? This covers only the streaming aspects of ffserver / ffmpeg. All questions about parameters for ffmpeg, codec questions, etc. are not covered here. You should also read the ffserver.txt file in this directory. It contains roughly the same information. 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. 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 from my motherboard based sound card.] I understand that FreeBSD systems work just fine as well. 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-mp3lame flag turned on. LAME is important as it allows streaming of 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: ./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://:8090/test.asf You should see (after a short delay) 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. 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. 5. Troubleshooting * I don't hear any audio, but video is fine Maybe you didn't install LAME, or get your ./configure statement right. 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 setup 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. * The audio and video loose sync after a while. Yes, they do. * After a long while, the video update rate goes way down in WMP. Yes, it does. Who knows why? * 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 different object ids that you can use, one of them -- the old one -- cannot play very well, and the new one works well (both on the same system). However, I suspect that the new one is not available unless you have installed WMP 7]. 6. What else can it do? There seems to be a bunch of code that allows you to replay previous video. I've never tried it, so it probably doesn't work properly. YMMV. In fact, in order to get some level of stability, ffserver now deletes all the previously sent video whenever it restarts. 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 the 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.] 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 real time. 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 says that the stream should start 5 seconds in the past -- and so the first 5 seconds of the stream is 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.