Streaming and transcoding

The three ways a file can be sent#

The player with its quality and stats overlay

Every time you press play, Fliks compares the file against what your device says it can handle, and picks the cheapest option that still works:

Method	What happens	When it's used
Direct Play	The file is sent exactly as stored, with nothing re-encoded or repackaged	The container, video codec and audio codec are all in your device's supported list, the resolution and bitrate are within its limits, and nothing else (see below) forces a change
Direct Stream (shown in the app as "Remux")	The video is copied without re-encoding, just repackaged into a streaming-friendly container	The video itself is compatible but the container or the audio track isn't
Transcode	The video is re-encoded, at a quality your device can decode, and packaged for adaptive streaming	Nothing above applies: an incompatible codec, a bitrate over your limit, HDR your screen can't show, or a feature (like burned-in subtitles) that needs it

A few specific things always force a transcode, no matter how compatible the codec otherwise is: subtitles that have to be burned into the picture (any image-based track you turn on, such as PGS or VobSub), black bars detected in the file while automatic black-bar cropping is on (it is by default, unless your device crops them itself), HDR that your screen can't display, and deliberately picking a lower quality than the source. If letterboxed films never Direct Play, the cropping setting is the usual reason.

The player's Stats for nerds overlay shows which of the three methods is active for whatever you're watching, plus the exact reason if it isn't a plain Direct Play.

Picking a quality#

The quality menu always offers Auto, plus a fixed ladder of resolutions with their target bitrate (2160p, 1080p, 720p, 480p, 360p, 240p, 144p), and Original when the source can be copied as-is. An HDR stream kept in HDR stops at 480p. Show low-bandwidth qualities (on by default, in App settings > Playback) adds lighter "eco" rungs at 2160p, 1080p and 720p, meant for a slow connection.

What "Auto" does depends on an admin setting:

Direct Play prioritized (the default, recommended for a home server on a local network): Auto plays the file as-is whenever it can, with no adaptive bitrate switching.
Adaptive streaming prioritized (ABR): Auto always goes through the adaptive ladder (an HLS stream, the segmented format every client plays, offering several qualities), so quality can step down automatically if the connection gets worse mid-playback.

Picking a specific resolution by hand always locks it in and disables adaptive switching, whichever mode is active; picking one equal to the source resolution can still Direct Play.

HDR and Dolby Vision#

An HDR10, HLG or Dolby Vision source is kept as HDR whenever it can be: a Direct Play or a Direct Stream never touches it, and a transcode keeps it in HDR when your device supports HDR and the server has an encoder that writes HDR correctly. H.264 has no HDR output at all. In hardware, HDR output is available for HEVC on Intel QSV and NVIDIA NVENC, and for AV1 on NVENC; every other backend hands an HDR transcode to the CPU encoder (much slower). A Dolby Vision profile 5 file, which has no HDR10 base layer, is always converted unless your device can play Dolby Vision itself.

When none of that is possible, HDR is tone-mapped down to SDR instead, so the picture still looks right rather than washed out or over-bright on a screen that can't display HDR. Which tone-mapping method runs (HDR → SDR tone-mapping algorithm, Auto by default) and the curve it uses (HDR → SDR tone-map curve, hable by default) are admin settings under Settings > Streaming, and a desktop client with its own tone-mapping capability (see Desktop) can ask the server to skip this step and hand over the untouched HDR stream instead. A viewer can also force the SDR conversion for their own device with Disable HDR in App settings > Playback.

Audio#

An HLS stream carries one output codec per group of audio tracks: if every track in a title already shares one codec your device supports, they're all copied as-is; otherwise Fliks converts every track in the group to a single common codec (preferring a surround format when the source and your device both support it, falling back to AAC otherwise). Each audio track is still its own switchable rendition, so changing the audio track mid-playback doesn't restart the video.

Hardware acceleration#

Encoding happens on whichever hardware path the server finds at startup (Intel QSV, VAAPI, NVIDIA NVENC, AMD AMF or Apple VideoToolbox, depending on the platform), with a plain CPU encode as the fallback if nothing else works. Hardware acceleration has the probe order per platform, which codecs each path encodes, and how to give the server access to a GPU.

On a server with more than one GPU, Settings > Streaming > GPU device picks which one handles transcoding (the picker only appears once a second GPU is actually detected); left on Automatic, Fliks uses the first one it finds.

Admin settings#

Settings > Streaming, in addition to the tone-mapping and GPU settings above:

Setting	What it does
"Auto" quality behavior	Direct Play prioritized vs. adaptive streaming prioritized, described above
Embedded subtitle extraction	When embedded subtitles are extracted: when playback starts (the default), at import and rescan, or on demand only
Segment duration	Length of each HLS segment (default 3 seconds)
First segment duration	A shorter first segment to speed up startup; later segments use the normal duration
Automatic black bar cropping	On by default. Removes black bars detected at import, at the cost of a re-encode; turn it off to keep the bars and allow Direct Play
Encoding preset (QSV / libx264)	Speed-versus-quality tradeoff (default `faster`); has no effect on VAAPI or NVENC
Concurrent background jobs	How many FFmpeg jobs can run at once for scans, thumbnails and marker detection (playback transcodes aren't limited by this)
Cache size limit / retention	How much disk the transcode cache may use, and how long a cached segment is kept, with a manual "Clear cache" action