After much testing, I could not foresee any technical reason why the
Second or ‘B Channel’ of vMix Replay could not be controlled (play, pause, jog, shuttle) using an external control surface. This feature would add considerable value to any sports production. There were no issues in throughput to encode four HD-SDI channels and playback two HD-SDI channels simultaneously using the 2TB WD Caviar Black HDDs. Even less of an issue when using the SSD drives, as would be expected. Windows Task Manager reported 25-35% CPU usage when in this six channel mode vMix Replay mode. The vMix Replay logs reported no problems, nor the statistics dialog (Source dropped = 0, Render dropped = 0, Resync = 0), which is very pleasing.
In this scenario, with four HD-SDI inputs being recorded at 1920x1080 i50, 100mbps and the vMix Replay applet with both A & B synchronized in playback mode, I added an additional video input which accessed the recording file (MPEG-PS) for the first channel and commenced playback. Then a second video playback of the second vMix Replay channel, and so forth to stress test the computer system and the MPEG encoders/decoders. Seven video record/playback channels appeared to be the limit, which in itself is impressive for a software based video production system.
The sources used for the tests were four DVB-T tuners/receivers connected to four HDMI/HD-SDI converters, and then fed to the BlackMagic Decklink Duo2 (4 Channel input) video card. It was important to use video sources that provided complex encoding scenarios, for the tests to be valid in the real world.
Having read through all the Posts in the ‘Instant Replay’ section of the Forum, which by the way provided a great insight to a broad range of requests, it would seem that this ‘B’ channel feature is important to many Users. Thanks to curtismacd31, stevespaw, tomotom1976, jens, HighViewSport, Rinsky and admin for the providing their thoughts on this subject.
It would be beneficial to vMix and its Users to have this feature, with the covenant that the PC system must be moderately spec’d to provide the resources needed to facilitate this feature. The responsibility of which is wholly that of the User, and not a reflection on the performance of vMix.
To add this feature to vMix Replay, would not require much in the way of additional coding. The features and workflow would remain for the most part as it is currently. The automation stays in place. The only addition would be those related to the system shortcuts/api for Instant Replay. These would include, but not limited to:
B_ReplayChangeDirection
B_ReplayChangeSpeed
B_ReplayJumpFrames
B_ReplayJumpToNow
B_ReplayPlayPause
B_ReplaySetSpeed
B_ReplaySetDirectionBackward
B_ReplaySetDirectionForward
ReplayABSynchronized (Description: Toggle Replay A+B synchronised On/Off)All other operations and functions would be performed using the ‘A’ Channel or the ‘Events’ grid/dialogue. Essentially, the feature request is about controlling the ‘B’ Channel for playback of replays at a point in time of the User’s choosing, whilst in the Manual mode. Transitions between the ‘A’ and ‘B’ channels shall be performed manually, either directly on the vMix interface or remotely via a control surface and shortcuts.
The system specifications on which the tests were performed are: Z170 motherboard, i7 6700 3.4GHz Quad Core processor, NVidia 4GB GTX960 video card, 16GB 3000MHz RAM, 2 x 500GB Samsung SSD and 2 x 2TB WD Caviar Black HDD. HD-SDI capture and playback courtesy of BlackMagic Decklink Duo2 (4 Channel input) and Decklink SDI (2 Channel output). Control surface is a Behringer PL-1 and touchscreen.
Currently we have vMix 4K (single channel replay), and wish to upgrade to vMix Pro and version 18 when released, but with no control of the vMix Replay ‘B’ channel, it is a deal-breaker. Martin, I hope that you are able to embrace the workflows that many of your customers are presently using with other replay systems, and the expectation of Directors/Producers in providing such replays.
Above: vMix with seven simultaneous video channels.