Cast a multi-GB video without a media upload

Start with the file and default quality

1. Open Cast to Your TV and select the video from your device.
2. Leave gear → Quality on Original initially.
3. Allow local inspection and automatic preparation to finish.
4. Press Cast in desktop Chrome and choose the TV. Keep Chrome open and the computer awake.

Preparation time is not an upload progress indicator: the app has no media-upload conversion service. For mobile playback, check the Android or iPhone and iPad route before starting a long screening.

How incremental reading keeps memory bounded

The selected file stays available through the browser’s local File interface. The media engine reads portions of it through a small cache, prepares fragmented MP4 output and applies backpressure so it does not endlessly produce data ahead of playback. Seeking starts work near the requested position rather than requiring a complete converted film first.

Compatible H.264 tracks can retain compressed picture data. Audio conversion can also run incrementally when the required local decoder is available. This makes compatible multi-GB files possible without buffering their full size. It does not make an unsupported codec playable or eliminate the CPU, memory and wireless throughput required during playback.

Why a 256 MiB message can still appear

There are two preparation routes. Incremental preparation handles compatible tracks without a whole-file size cap at 256 MiB. The older FFmpeg WebAssembly fallback handles some other formats by converting the whole file; that path has 256 MiB input and output limits. Subtitle burn-in uses the same restricted route.

A 6 GB file with compatible tracks can therefore be usable while a much smaller file needing an unavailable decoder cannot prepare. An MKV or MOV extension does not identify those tracks reliably. A larger subscription does not unlock a bigger fallback buffer: this limit protects the browser’s conversion workload, while plan limits concern accumulated playing time.

Use text subtitles for long films

Supported embedded text subtitles in MKV/WebM and MP4/MOV are inspected in bounded chunks, with no 256 MiB limit on the whole video. The converted caption text is limited to 5 MiB. Separate SRT, WebVTT, ASS and SSA sidecars also have a 5 MiB limit.

Choose a selectable text track in Subtitles when possible. Preserving ASS styling or displaying bitmap subtitles may require burn-in and thus whole-file conversion. If a large film already plays, adding burn-in can move it onto a route it is too large to use. The subtitle guide explains these options.

Keep a long screening stable

Keep the source device powered and awake. On a phone, keep the browser visible and the device unlocked; background playback is not guaranteed. Avoid reloading the page, because that loses the selected local file. On-screen preparation success is not a promise that every TV and network can sustain a high-bitrate film for its entire duration.

If playback buffers, compare 1080p or 720p with Original using the same section of video. Lowering output dimensions can reduce conversion and transmission demands, but does not solve TV discovery. Desktop Chrome and operating-system mirroring control their final encoding, so Original does not guarantee lossless, HDR or 4K delivery. For a file-specific failure, note the exact preparation message and read the format guide.