SSTV.org.uk

AVT mode

Amiga Video Transceiver AVT125 BW

Historical Amiga Video Transceiver compatibility and reference decoding.

Supported in app

Mode sample

BBC-style colour test card and app-generated audio

The image is generated locally for this mode's raster. For supported modes, the audio sample is encoded from that image with the SSTV Signal Desk transmitter code, then published as lossless FLAC for static playback.

FLAC, 48 kHz, 16-bit mono, 134.442 s.

AVT125 SSTV BBC-style colour test card
AVT125 source card, 320 x 400
AVT125 SSTV round-trip decoded test card
Receiver decoded AVT125 from the FLAC-restored WAV, 400 lines.

Round-trip decode evidence

Encoded, compressed losslessly, restored, then decoded.

The published FLAC is restored to WAV and passed through the SSTV Signal Desk receiver sample harness. The receiver decoded AVT125 from the FLAC-restored WAV and wrote 400 image lines for this AVT125 test card.

Open the generated decode report

Mode spec

Short nameAVT125
Support statusSupported in app
Spec statusSupported in app; public line-level timing was not found in checked sources, so app timing fields are labeled separately.
Duration125.000 s
Frame320 x 400
Data lines400
Public VISVIS 80 (0x50)
Standard VIS code0x50 (80)
Extended/N-VISNo
Color modelRGB
Component sequenceR-G-B
Line rate192 lpm
Public timing profileNo implementation-grade public line timing was found in checked sources; app implementation fields are listed separately.
App duration125.000 s
App frame320 x 400
App raw VIS0x50 (80)
App timing profileApp RX line fields: sync 0 ms; front porch 0 ms; back porch 0 ms; separator/blank 0 ms; video tones 1500-2300 Hz around 1900 Hz.
App RX sync0 ms
App RX front porch0 ms
App RX back porch0 ms
App RX separator/blank0 ms
App subcarrier1900 Hz
App deviation400 Hz
App tone range1500-2300 Hz

Strengths

  • AVT125 is a standard-length large-frame AVT mode: 125.000 s, 320 x 400, RGB.
  • AVT125 preserves AVT R-G-B RGB ordering while publishing the normal-code label VIS 80 (0x50) separately from the app raw VIS value.
  • AVT125 has explicit app timing fields: 0 ms sync, 0 ms front porch, 0 ms back porch, 0 ms separator/blank, and 1500-2300 Hz around 1900 Hz video tones.
  • AVT125 is documented from the app timing row; the line fields are explicit even where checked public sources do not publish every porch value.

Tradeoffs

  • AVT125's 125.000 s frame is a balanced choice, but it still needs a stable path for the full 320 x 400 scan.
  • AVT125 AVT public tables vary by source; use the app-generated sample audio when checking exact receive timing.

Source notes

AVT public mode tables vary and Dayton N7CXI excludes AVT timing because it did not have solid author data. This row presents the app-supported implementation with the public normal VIS label where available. App raw VIS 0x50 and app timing fields are generated from sstv/sstv/sstv/sstvparam.swift during the website build.