CineX Notes
Make every video open.
Long-form notes on containers, codecs, subtitles and playback compatibility — and how CineX actually handles your files.
Archive
Read in order.
What Is CineX? An iPhone, iPad and Mac App That Turns Videos You Can't Play into MP4
CineX is a video conversion app for iPhone, iPad and Mac that turns local videos that do not open easily into MP4. This guide explains how CineX chooses between a quick container change and a full conversion, where processing happens, how the 5 free successful conversions and one-time Opus purchase work, and the important limits around subtitles, HDR, DRM, spatial video and supported platforms.
Container vs Codec: Why Two Files Ending in .mp4 Can Behave Completely Differently
Why can two videos that both end in .mp4 behave completely differently? This guide separates the container—the package that holds video, audio, and subtitles—from the codec that determines how the media is stored. Learn why extensions alone cannot predict playback, how H.264, HEVC, VP9, AV1, and Xvid fit into the picture, and the three checks that make an unplayable file much easier to diagnose.
MKV vs MP4: The Difference Is the Container, Not the Picture Quality
MKV and MP4 are both video containers, so the extension alone does not determine picture quality. This guide compares their real differences in track flexibility, subtitle and audio handling, Apple-device compatibility, and everyday playback. It also explains when converting MKV to MP4 can leave the video stream untouched and when the picture must be processed again.
Remuxing vs Re-encoding: When a Video's Picture Data Never Has to Be Touched
Remuxing and re-encoding can both turn a video into a more usable MP4, but they do very different work. This guide explains why remuxing can preserve the picture stream and finish in seconds, why re-encoding usually takes minutes and changes the picture data, when each path is needed, and why file size alone cannot tell you whether picture quality changed.
A Video Won't Play on Your iPhone, iPad or Mac: First Tell a Broken File from an Unsupported One
When a video will not play on an iPhone, iPad or Mac, first separate a damaged file from a format-compatibility problem. This guide shows how to check file size, cross-test the same video on another device or app, and use readable basic metadata as clues. It then explains when you should obtain a fresh copy and when conversion to MP4 is the more relevant next step, including the limits of what CineX can and cannot solve.
MKV Won't Play on Your Mac: Switch Players, or Convert to MP4?
When an MKV will not play on your Mac, the useful question is not which container is “better,” but which route fits what you need to do next. This guide compares switching playback methods with converting to MP4, including cross-device use, conversion time, picture-quality limits, subtitles, multiple audio tracks, and the specific role and boundaries of CineX.
Converting MKV to MP4 Without Re-compressing the Video: When a Container Swap Is Enough
Converting MKV to MP4 does not always require re-compressing the video. This guide explains how H.264 and HEVC files can use a fast container-swap path, when codecs such as Hi10P, VP9, AV1, or Xvid require full re-encoding, and what that means for speed, HDR and Dolby Vision metadata, audio, subtitles, disk space, and protected content.
An MP4 Still Won't Play on Your Mac: Why the Right Extension Isn't Enough
Your file ends in .mp4, but your Mac still refuses to play it. The extension identifies a container—not the video codec inside. Learn how this differs from an unsupported MKV file, how to tell codec trouble from corruption or out-of-range video settings, and when CineX can convert the file. We also explain the limits: protected or damaged files cannot be fixed by conversion, and some picture features may change.
Why CineX Is Instant for Some Videos and Slower for Others: It Checks the Codec First
CineX does not choose a conversion path from an extension such as MKV or MP4. It reads the video codec inside the file first, then decides whether the existing picture can be kept while the container changes or whether the picture needs a full conversion. This article explains both paths, why two files with the same extension can take seconds versus minutes, and the current boundaries for demanding high-frame-rate material, no-audio files, and damaged sources.
What Happens to Subtitles After CineX Converts a Video: Text, ASS and PGS
What happens to subtitles when CineX converts a video depends on the subtitle type. Text tracks such as SRT and ASS are converted into embedded MP4 subtitles, while ASS positioning and color are reduced to plain text. PGS, VobSub and DVD image subtitles are not preserved and are currently skipped without a warning. This guide also covers external subtitle files, multiple tracks, and the Simplified-versus-Traditional Chinese distinction.
Does CineX Keep HDR and Dolby Vision? It Depends on Whether the Picture Is Re-encoded
Does CineX keep HDR10 and Dolby Vision when converting a video to MP4? The answer depends on the picture-processing path. A container-only change avoids recompressing the picture, passes through HDR10 static metadata, and can retain Dolby Vision metadata, with exceptions. Full re-encoding loses Dolby Vision metadata and converts 10-bit / HDR video to 8-bit. Learn what determines the path and why the difference matters before converting a file you want to preserve.
Where CineX Processes Your Video: Conversion Happens on Your Own Device
CineX converts video on your iPhone, iPad, or Mac, so the video file itself does not need to be uploaded for processing. This guide explains what that changes for large private files, where the original and converted copies remain, why local processing removes upload and download stages rather than all waiting, and the one separate exception: a simple free-conversion count can sync across your own devices through iCloud Keychain without containing video, subtitle, or filename information.
What You Get Free in CineX: How the First Five Successful Conversions Are Counted
CineX counts the first five successful conversions, not five attempts: failures, cancellations, and retries do not use the allowance, while deleting a finished file does not restore one. Learn how iCloud Keychain shares the count across devices on one Apple ID, why reinstalling does not reset it, and what changes when syncing is off.
How Much Is CineX Opus? A One-Time Purchase, and What It Unlocks
CineX Opus is a one-time purchase priced at US$8.99 in the U.S. and ¥38 in China, with no monthly or annual subscription and no auto-renewal. The purchase unlocks unlimited conversions only: it does not add a higher-quality mode, a faster mode, or broader format support. This guide also explains purchase restoration on a new device, what to test before paying, and the subtitle, HDR/Dolby Vision, DRM, and spatial-video limits that remain unchanged in Opus.
Before You Buy Opus: What to Test with Your Five Free Conversions
Before buying Opus, use CineX’s five free successful conversions on files that represent your real library: your most common file type, a subtitle-heavy video, HDR or Dolby Vision, your largest file, and a multi-audio-track title. This guide shows what to inspect, which limits stay the same after purchase, how storage can affect a large-file test, and when the results are a good reason not to buy.