rustdesk/rustdesk · error

Failed to get decode context

Error message

Failed to get decode context

What it means

VramDecoder::new first calls try_get(format, luid) to find a usable hardware decode context (a device/format combination matching the requested codec and optional LUID). If no context matches, `ok_or` produces `Failed to get decode context`. The requested hardware decoding configuration has no candidate on this machine.

Source

Thrown at libs/scrap/src/common/vram.rs:356

            .vram_decode
            .drain(..)
            .filter(|c| c.data_format == data_format && c.luid == luid && luid != 0)
            .collect()
    }

    pub fn possible_available_without_check() -> (bool, bool) {
        if !enable_vram_option(false) {
            return (false, false);
        }
        let v = crate::hwcodec::HwCodecConfig::get().vram_decode;
        (
            v.iter().any(|d| d.data_format == DataFormat::H264),
            v.iter().any(|d| d.data_format == DataFormat::H265),
        )
    }

    pub fn new(format: CodecFormat, luid: Option<i64>) -> ResultType<Self> {
        let ctx = Self::try_get(format, luid).ok_or(anyhow!("Failed to get decode context"))?;
        log::info!("try create vram decoder: {ctx:?}");
        match Decoder::new(ctx) {
            Ok(decoder) => Ok(Self { decoder }),
            Err(_) => {
                HwCodecConfig::clear(true, false);
                Err(anyhow!(format!(
                    "Failed to create decoder, format: {:?}",
                    format
                )))
            }
        }
    }
    pub fn decode<'a>(&'a mut self, data: &[u8]) -> ResultType<Vec<VRamDecoderImage<'a>>> {
        match self.decoder.decode(data) {
            Ok(v) => Ok(v.iter().map(|f| VRamDecoderImage { frame: f }).collect()),
            Err(e) => Err(anyhow!(e)),
        }
    }

View on GitHub (pinned to 91c9fccbb0)

Solutions

1. Fall back to software decoding when VramDecoder::new fails, using the negotiated codec's software path.
2. Check GPU capability/driver support for the requested codec format before attempting hardware decode (supported_decodings / codec capability checks).
3. Clear the cached HwCodecConfig (the code already clears on decoder-create failure) so adapter detection re-runs, then retry.
4. Verify the luid passed matches the adapter actually used for capture/decode; pass None to let try_get pick any capable adapter.

Example fix

// before
let decoder = VramDecoder::new(format, Some(luid))?;
// after
let decoder = match VramDecoder::new(format, Some(luid)) {
    Ok(d) => d,
    Err(e) => {
        log::warn!("vram decode unavailable ({e}), using software decoder");
        Decoder::new_software(format)?
    }
};

let can_hw_decode = supported_decodings()
    .iter()
    .any(|d| d.codec_format == format);
if !can_hw_decode {
    // construct software decoder instead of VramDecoder::new
}

// Rust: match on Result
match VramDecoder::new(format, luid) {
    Ok(d) => d,
    Err(e) if e.to_string().contains("Failed to get decode context") => {
        log::warn!("no hw decode ctx for {format:?}, software fallback");
        Decoder::new_software(format)?
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: Constructing VramDecoder::new(format, luid) where try_get returns None — no adapter/dxgi device supports the requested CodecFormat, or the supplied luid does not match any detected decode-capable adapter.

Common situations: Remote machine GPU lacks H264/H265 hardware decode (or drivers are too old); the peer negotiated a codec the local GPU cannot hardware-decode; stale HwCodecConfig cache lists adapters that no longer exist (driver update, dock/monitor change); passing a luid from a different adapter than the capture one.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• unsupported format: {:?} -> {:?}
• Failed to create decoder, format: {:?}
• not texture frame
• encoder type mismatch
• rotation not supported

AI-assisted analysis of rustdesk/rustdesk@91c9fccbb0 (2026-09-10). Data as JSON: /api/errors/76a6b5fead45f985. Report an issue: GitHub.