A decoder is the software or chip that takes a compressed video stream and turns it back into the actual pictures you see on screen. Every device that plays video — your phone, your TV, your laptop, a Zoom client — runs a decoder constantly. If a video doesn't play, nine times out of ten the problem is that the device's decoder doesn't recognise that particular codec.
Two kinds matter in practice. Hardware decoders are dedicated chips built into a phone's processor, a TV's main board, or a graphics card. They're fast and use almost no battery — that's how your phone plays 4K HDR for hours without getting hot. Software decoders are programs that do the same job using the CPU; they work on any device but burn battery and CPU cycles, which is why low-end phones get hot and choppy when playing AV1 video they can't decode in hardware.
For a streaming product, decoder support is the gating constraint on which codecs you can deliver. In 2026, every device decodes H.264 in hardware. Most devices from 2017 onward decode HEVC in hardware. AV1 hardware decode is now broadly available — Netflix reports 88 % of large-screen devices certified since 2021 support it, and most TVs since 2022 ship with AV1 silicon. Anything older falls back to software decoding (acceptable up to 1080p AV1, painful at 4K) or has to be served the H.264 fallback rendition.
