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41 <h3>Ben Hutchings</h3>
46 <h1>What is DVswitch?</h1>
47 <ul class="incremental">
49 A software system that supports video mixing, recording and streaming
52 Designed particularly for the needs of technical conferences that
53 want to record and stream on a limited budget. Now used more
54 widely, often without streaming.
57 Mixing is <em>live</em> - a requirement for streaming, and a way to
58 avoid the need for extensive editing after the event
61 Mixing is <em>interactive</em> - a requirement for good coverage of
62 presenters, audience and slides, but very limited in other
69 <h1>What is DVswitch <em>not</em>?</h1>
71 There are limited developer resources and limited goals for
72 DVswitch. It is never intended to be:
74 <ul class="incremental">
76 A general video editor
79 An audio mixer (but it does implement audio dubbing and level monitoring)
82 A complete recording and publishing system
85 <p class="incremental">
86 These are all better handled by other software and
92 <h1>The 'DV' in DVswitch</h1>
94 The name refers to the DV formats used by many video cameras:
98 <th>Profile</th><th>Specification</th><th>Video codec</th><th>Supported</th>
101 <td>Basic DV</td><td>IEC 61834</td><td>DV 25</td><td>yes</td>
104 <td>DVCAM</td><td>Sony proprietary</td><td>DV 25</td><td>probably</td>
107 <td>DVCPRO</td><td>SMPTE 314M</td><td>DV 25</td><td>probably</td>
110 <td>DVCPRO50</td><td>SMPTE 314M</td><td>DV 50</td><td>not yet</td>
113 <td>DVCPRO HD</td><td>SMPTE 370M</td><td>DV 100</td><td>not yet</td>
116 <td>HDV</td><td>IEC 61834</td><td>MPEG-2</td><td>no</td>
120 DV video codecs compress each frame separately (unlike MPEG)
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124 The lack of interframe compression means there is relatively
125 little delay between camera and mixer and we can cut between
126 sources without having to decode all sources all the time.
127 In fact, DVswitch doesn't need to decode even a single source at
128 full frame rate if you just cut between sources without using
132 Unfortunately, most of today's consumer cameras don't have DV
133 output and may not provide live video output at all.
139 <h1>Overview of the system</h1>
141 A simplified view of the typical components:
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148 <ul class="incremental">
150 Source types: firewire/USB DV device, ALSA capture device,
154 Physical sources are spread around room and connected to the
155 mixer via TCP/IP networking
158 Original protocol: mixer runs a network server; sources run as
159 clients and send DIF over TCP
160 <ul class="incremental">
162 Requires a script to coordinate mixer and source startup -
163 an annoying complication
166 Improvement: tally lights
170 Next release: sources run as RTP/RTSP servers and mixer
171 connects to them as a client
172 <ul class="incremental">
174 No custom scripts required; just configuration files
183 <ul class="incremental">
185 Sink types: DIF files, pipe to arbitrary command
188 Also connected using TCP/IP networking, though this is not such
189 a good idea for recording
192 Original protocol: mixer runs a network server; sinks run
193 as clients and receive DIF over TCP
194 <ul class="incremental">
196 Improvement: sink reports whether it will record; mixer can
197 start, stop and cut recording
202 Next release: file and pipe sinks built into mixer along with an
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