Codec Matrix

The release binary bundles every video encoder + decoder backend the edge knows about — libx264, libx265, NVIDIA NVENC + NVDEC, Intel QSV (x86_64 only), and VAAPI. At startup the hardware probe walks the active set, opens a minimal session against each, and advertises capability bits on HealthPayload.capabilities for the ones that actually work on this host. The manager UI keys per-output codec dropdowns off those bits.

This page covers the static support matrix, the *_auto resolver that does the right thing without operator hand-holding, and the verification commands for confirming what activated on a given host.

Pick `*_auto` unless you have a reason not to

For most operators the right answer on video_encode.codec is h264_auto or hevc_auto. The edge resolves Auto on flow start against the host’s probed capabilities and the requested chroma + bit-depth, picking the cheapest backend that handles the combination:

Family + chroma + bit-depth	Resolver chain (head → tail)
H.264 + 4:2:0 + 8-bit (the dominant distribution path)	NVENC ≻ QSV ≻ VAAPI ≻ libx264
H.264 + anything else	libx264 (no HW H.264 backend supports 4:2:2 / 10-bit / 4:4:4)
HEVC + 4:2:0 + 8-bit	NVENC ≻ QSV ≻ VAAPI ≻ libx265
HEVC + 4:2:0 + 10-bit	NVENC ≻ VAAPI ≻ QSV ≻ libx265
HEVC + 4:2:2 + 8-bit	VAAPI (Intel iHD) ≻ libx265
HEVC + 4:2:2 + 10-bit	VAAPI (Intel iHD) ≻ libx265
HEVC + 4:4:4 (any)	libx265 (HW backends reject NV24 today)

Operators who need wire-level reproducibility (compliance deployments, vendor-specific bitstream behaviour) pick an explicit backend — the manager UI cross-validates the chroma + bit-depth combo before flow start, so an invalid combination fails at save time, not at flow bring-up.

Video encode — pixel-format / bit-depth matrix

Backend	4:2:0 / 8	4:2:2 / 8	4:2:0 / 10	4:2:2 / 10	4:4:4
libx264 (CPU, `video-encoder-x264`)	✓	✓	✓	✓	✓
libx265 (CPU, `video-encoder-x265`)	✓	✓	✓	✓	✓
h264_nvenc (NVIDIA, `video-encoder-nvenc`)	✓	✗	✗	✗	✗
hevc_nvenc (NVIDIA, `video-encoder-nvenc`)	✓	✗	✓	✗	✗
h264_qsv (Intel, `video-encoder-qsv`)	✓	✗	✗	✗	✗
hevc_qsv (Intel, `video-encoder-qsv`)	✓	✗	✓	✗	✗
h264_vaapi (Linux, `video-encoder-vaapi`)	✓	✗	✗	✗	✗
hevc_vaapi (Intel iHD Tiger Lake+)	✓	✓	✓	✓	✗ (NV24 deferred)
hevc_vaapi (AMD radeonsi)	✓	usually ✗	✓	usually ✗	✗

Implication for broadcast 4:2:2 contribution: on NVIDIA-only and AMD-only hosts there is no GPU path for 4:2:2 10-bit; libx265 is the only option. Intel Tiger Lake+ iGPUs have the full broadcast HEVC matrix through VAAPI.

Static rejection happens at config validation and at encoder open, so an operator who bypasses the manager UI still gets a precise error before any frame is encoded.

Video decode — coverage by path

Backend	Display output (KMS)	TS → TS transcode	Notes
libavcodec (CPU)	✓ (fallback)	✓ (universal)	Every format, every bit-depth.
NVDEC (`video-decoder-nvdec`)	✓ zero-copy scanout	✓	x86_64; 4:2:0 only.
QSV decode (`video-decoder-qsv`)	✓	✓	x86_64; 4:2:0 only.
VAAPI decode (`video-decoder-vaapi`)	✓ zero-copy DMA-BUF	✓	Linux; Intel iHD does 4:2:2 + Main10.

Auto resolution priority — both the display path and the transcode input-decode path share the same priority:

VAAPI ≻ NVDEC ≻ QSV ≻ CPU

The display path also relies on KMS atomic-commit zero-copy via DRM PRIME (see Display Output); the transcode path doesn’t get the same fast scanout but still benefits from offloading decode to dedicated silicon.

Audio codec matrix

Codec	Encode	Decode	Sample rates	Channels	Notes
AAC-LC	FDK-AAC in-process (`fdk-aac`)	FDK-AAC	8 k – 48 k	1 – 8	Production AAC, lowest latency.
HE-AAC v1	FDK-AAC	FDK-AAC	8 k – 48 k	1 – 2	SBR adds chroma-bandwidth dependency.
HE-AAC v2	FDK-AAC	FDK-AAC	8 k – 48 k	2 (stereo only)	Parametric Stereo — manager UI hard-filters mono.
Opus	libopus via libavcodec	libopus via libavcodec	48 k	1 – 2	Decode wired; transcode-from-Opus-on-TS works.
MP2	libavcodec	libavcodec	32 k / 48 k	1 – 2	DVB-T / SD broadcast.
AC-3	libavcodec	libavcodec	32 / 44.1 / 48 k	1 – 6 (5.1)	ATSC / Blu-ray.
E-AC-3	(passthrough only)	libavcodec	—	1 – 7.1	UHD ATSC 3.0.
PCM (ST 2110-30 / -31)	passthrough	passthrough	48 k / 96 k	1 – 16	Hardcoded sample-rate in config.
SMPTE 302M	inline mux	inline demux	matches input	matches input	`transport_mode: audio_302m` on SRT / UDP / `rtp_audio`.

Capability strings on `HealthPayload.capabilities`

Edges advertise the following when the matching feature is compiled in and the runtime probe finds the underlying driver / GPU usable. Anything missing is disabled in the manager UI dropdowns with a tooltip.

Capability	Source	Meaning
`video-encode`	any of x264 / x265 / nvenc / qsv / vaapi	Edge can re-encode video at all.
`video-encoder-x264`	`video-encoder-x264`	libx264 available.
`video-encoder-x265`	`video-encoder-x265`	libx265 available.
`video-encoder-nvenc`	`video-encoder-nvenc` + probe	h264_nvenc / hevc_nvenc available.
`video-encoder-qsv`	`video-encoder-qsv` + probe	h264_qsv / hevc_qsv available.
`video-encoder-vaapi`	`video-encoder-vaapi` + probe	h264_vaapi / hevc_vaapi available.
`video-decoder-nvdec`	`video-decoder-nvdec` + probe	NVDEC available (transcode + display).
`video-decoder-qsv`	`video-decoder-qsv` + probe	QSV decode available.
`video-decoder-vaapi`	`video-decoder-vaapi` + probe	VAAPI decode available.
`display`	`display` + ≥ 1 KMS connector enumerated	Local-display output usable.
`fdk-aac`	`fdk-aac`	In-process AAC family.
`media-codecs`	`media-codecs` (default on)	libavcodec video decode + Opus / MP2 / AC-3.
`webrtc`	`webrtc` (default on)	WHIP / WHEP supported.
`tls`	`tls` (default on)	HTTPS + RTMPS.
`replay`	`replay` (default on)	Recording + clip playback.

The resource_budget.hw_encoder_chroma block on the same payload carries the per-(codec, chroma, bit-depth) matrix with one boolean per cell — that’s the source of truth the manager UI reads when graying out 4:2:2 chroma against NVENC.

What `*_auto` activates on each host class

Static support is one thing; what your host actually opens at runtime is another. Common combinations:

Host class	Auto resolves to (H.264 4:2:0 8-bit)	Auto resolves to (HEVC 4:2:2 10-bit)
x86_64 NVIDIA	NVENC	libx265 (NVENC rejects 4:2:2)
x86_64 Intel Tiger Lake+ iGPU	QSV (or VAAPI if explicitly preferred)	VAAPI (iHD does 4:2:2 + Main10)
x86_64 AMD	VAAPI	libx265 (AMD radeonsi rejects 4:2:2)
aarch64 NVIDIA Jetson	NVENC	libx265
aarch64 AMD APU SBC	VAAPI	libx265
Headless / no GPU	libx264	libx265

Verification — confirm Auto activates the right backend

Inspect the host capability matrix. Start the edge and curl /api/v1/stats/health (or open the manager Node detail → Resources card):
Terminal window
```
curl https://edge:8443/api/v1/stats/health \
     -H "Authorization: Bearer $TOKEN" | \
  jq '.resource_budget.hw_encoder_chroma'
```
On Tiger Lake+ Intel iHD: hevc_vaapi_yuv422_10bit = true. On AMD radeonsi: hevc_vaapi_yuv422_10bit = false. On any host with NVENC: every hevc_nvenc_yuv422_* cell is false.
Confirm Auto resolution lands on the expected backend. Create a flow with video_encode.codec = "h264_auto", chroma yuv420p, 8-bit. Watch the edge logs for:
```
video_encode auto-resolved 'h264_auto' → <backend>
```
On an NVIDIA host this prints → nvenc_h264; on Intel Tiger Lake+ → qsv_h264 (or → vaapi_h264 with explicit preference); on AMD → vaapi_h264; on a host without any compiled-in HW backend that the probe could open → libx264.
Confirm an invalid combination is rejected up front. Create a flow with video_encode.codec = "h264_nvenc", chroma yuv422p. The manager preflight returns HTTP 422 + error_code: encoder_chroma_not_supported before the WS round-trip — the flow never reaches the edge.
Confirm HW transcode decode activates. Set video_encode.hw_decode = "auto" (the default) on a flow that decodes a source video. Edge logs:
```
ts_video_replace: opened HW decoder (backend=Vaapi)
```
(or Nvdec / Qsv). Running perf top against the edge process should show av_hwframe_transfer_data in the hot path (sysmem download) but no libavcodec_decode_h264 — the decode itself ran on the GPU.

Cost model — pixel-rate aware

Per-flow cost units scale with pixel rate. The HW vs SW base is the dominant axis: HW backends start at base 100, software at base 500.

units = base × (width × height × fps) / (1920 × 1080 × 30)
        × 1.5    if bit_depth == 10
        × 1.33   if chroma == yuv422p
        × 2.0    if chroma == yuv444p

Examples:

Profile	Approximate units
1080p25 H.264 4:2:0 8-bit on NVENC	~83
1080p50 H.264 4:2:0 8-bit on NVENC (3G-SDI tier-1)	167
1080p59.94 H.264 4:2:0 8-bit on NVENC	200
1080p50 HEVC 4:2:2 10-bit on NVENC (broadcast contribution)	313
4K30 H.264 4:2:0 8-bit on NVENC	400
1080p50 H.264 4:2:0 8-bit on libx264	833
4K50 HEVC 4:2:2 10-bit on libx265 (broadcast contribution)	~6 650
4K59.94 HEVC 4:2:2 10-bit on libx265 (broadcast contribution)	~7 980
4K59.94 HEVC 4:2:0 8-bit on libx265	~4 800

The per-host budget is 1000 + 200 × physical_cores, so a 4-core edge gets 1 800 units, a 32-core EPYC gets 7 400. See Resources & Capacity for the per-family HW session caps and how oversubscription is surfaced.

Codec Matrix

Pick *_auto unless you have a reason not to