Troubleshooting

Unsupported Video File Errors: What the Message Really Means

A video file is not supported when the app does not recognize its container, cannot decode the codec inside it, cannot read it because it is damaged or incomplete, or is blocked from reading it by DRM protection. A media inspector such as MediaInfo shows the real container and codecs in seconds. From there, the fix is usually a lossless remux into a common container, a conversion to H.264 MP4, or extracting the audio when that is all you need.

6 min read · Updated

The many messages behind not supported

Apps word the error differently, but most fall into a few groups:

  • File type not supported, or the file simply cannot be selected in an upload dialog.
  • Codec not supported, or a player that shows sound but a black picture, or a picture with no sound.
  • This file cannot be played, or an error part way through playback.
  • An upload that starts and then fails during processing.
  • Nothing happens at all when the file is opened.

Each points somewhere slightly different, but the diagnosis below covers them all.

Container, codec and extension: three different things

A video file is a container, such as MP4, MOV, MKV or WebM, holding compressed streams made with codecs, such as H.264, HEVC or VP9 for video and AAC or Opus for audio. The extension is just a label on the name. An app can support the container but not the codec inside it, and a file can carry the wrong extension entirely. The browser video muxing article explains containers and codecs in more depth; for troubleshooting, it is enough to know that all three must line up with what the app accepts.

Common causes of unsupported file errors

  • An uncommon container. Camcorder MTS and M2TS files, older AVI, WMV and FLV files, broadcast MXF and old phone 3GP files are refused by many apps.
  • An extension that does not match the content, after a manual rename, a download that guessed wrong, or a missing extension.
  • A codec the app cannot decode, such as 10-bit HEVC on older devices, ProRes outside editing software, AV1 on older hardware or legacy codecs from old cameras; HEVC compatibility covers the most common case.
  • An unusual audio codec, which can make an otherwise normal file fail in some apps.
  • A damaged or incomplete file. Recordings interrupted by a full card, a flat battery or a crash can be missing the index that MP4 and MOV files rely on, and partial downloads stop early.
  • An online-only cloud file. Synced folders can list files whose contents have not yet been downloaded to the device.
  • DRM protection. Purchased, rented and streaming downloads are usually encrypted and play only in authorized apps.
  • A limit that is not about format, such as an app's maximum length or size.

Inspect the file in this order

  1. Check the size against the length. A one-hour video of a few kilobytes is an online-only cloud file or a broken download.
  2. Try VLC. It plays a very wide range of formats, so if VLC fails too, suspect damage or DRM.
  3. Open the file in MediaInfo, or run the ffprobe command below in a terminal, and note the real container, the video codec with its profile and bit depth, and the audio codec.
  4. Compare those details with the formats the app accepts, not just the extension.
  5. Think about where the file came from. Purchases, rentals and app downloads from streaming services point to DRM.
  6. If the inspector reports errors or a missing duration, treat the file as damaged.

ffprobe -hide_banner mystery-file.mp4

Remux, convert or extract the audio

Remux when the codecs are fine but the container is not. Copying streams into a new container is fast and lossless. MKV accepts almost any codec, so it is the safest target:

ffmpeg -i camera.mts -c copy camera.mkv

Convert when the codec itself is the problem. Re-encoding to H.264 video and AAC audio in MP4 gives the widest compatibility, at a cost in time and some quality:

ffmpeg -i old-recording.avi -c:v libx264 -crf 20 -c:a aac -b:a 160k old-recording.mp4

Extract the audio when you only need a transcript, subtitles or a translated voice. Audio formats are less fussy, and the file is much smaller:

ffmpeg -i lecture.wmv -vn -c:a libmp3lame -q:a 2 lecture.mp3

Graphical tools such as HandBrake do the conversion step with presets, and converting video formats compares the options. For damaged recordings, first try the camera maker's own software or recovery tools that rebuild a missing MP4 index using a healthy file from the same camera; success is not guaranteed. For DRM-protected files, ask the rights holder for an unprotected copy. Removing protection may break the terms of service and, in some countries, the law; this is not legal advice.

A worked example: camcorder files from a conference

MTS files, refused by an upload form

Suppose an events team records a 45-minute keynote on a camcorder that saves MTS files, and their translation tool's upload form will not even let them select the file. MediaInfo shows H.264 video and AC-3 audio inside an MPEG transport stream: common codecs, uncommon container. Remuxing to MKV takes under a minute and loses nothing, and the new file is accepted. The team keeps the original MTS files, because remuxing copied the streams rather than replacing them.

Pitfalls and limits

  • Renaming a file never converts it. A renamed MTS file is still an MTS file with a misleading name.
  • Remuxing cannot fix a codec the app does not support; only conversion can.
  • Each lossy conversion costs some quality, so convert from the original, once.
  • Badly damaged files may be partly or wholly unrecoverable.
  • DRM-protected files cannot be processed by ordinary tools, by design.
  • Converting very long or high-resolution files takes significant time and disk space; check free space before starting.

Formats mydubly accepts and what it produces

Video input
MP4, MOV, WebM, MKV and M4V
Audio input
MP3, WAV, M4A, AAC, OGG and FLAC
Length
Up to 2 hours per file
Audio tracks
One track is used, so the speech should be the only or main track
Source
A file on your device; importing from a URL or link is not supported
Outputs
Transcripts, SRT and VTT subtitles, a translated transcript, or a translated voice track and video

The browser decodes the audio locally and uploads only compressed audio chunks, so the video stays on your device. In a translated video the picture is copied rather than re-encoded, and if the video codec cannot go into MP4 the output is MKV. If a file in one of these containers is still refused, the codec inside is the likely reason, and converting to H.264 MP4 is the dependable fix. Why some processing happens on your device and some on a server is covered in browser-based video processing.

When another workflow fits better

  • If you only need text or translated audio, extracting the audio and using the audio route avoids video codec issues entirely; extracting audio from a video shows how.
  • For professional camera formats, convert in the editing software that already reads them.
  • For protected content you do not own, contact the owner rather than working around the protection.

Next step: inspect, then fix once

Run MediaInfo on the file, decide whether it needs a remux or a conversion, keep the original, and upload the result to the video translator, or to video to text for a transcript. Format-specific notes, such as for MKV files, cover the details of each container.

Frequently asked questions

Why does my MP4 play in VLC but not in other apps?

The container is fine, but the codec inside may not be. MP4 can hold HEVC, AV1 or unusual audio codecs that some apps and devices cannot decode. Check the codecs in MediaInfo, and convert to H.264 video with AAC audio for the widest compatibility.

Is it safe to just change the file extension?

Renaming only changes the label, not the content, so it rarely helps and can make later troubleshooting confusing. The exception is a file whose extension was wrong to begin with; even then, a remux to the matching container is more reliable than a rename.

Can I translate a video I bought from a streaming service?

Generally not. Purchased and rented videos from streaming services are usually DRM-protected, so ordinary tools cannot read them, and their terms typically restrict processing. Ask the rights holder for an unprotected copy or permission. This is general information, not legal advice.

My recording stopped when the battery died. Can the file be saved?

Sometimes. Interrupted MP4 and MOV recordings often lack the index written at the end. The camera maker's software or tools that rebuild the index from a healthy recording made with the same device may recover it. Work on a copy, never the only original.

Which video format is safest to upload almost anywhere?

An MP4 file with H.264 video and AAC audio is the most widely accepted combination across players, browsers, editors and upload forms. It is not always the smallest or highest quality option, but it is the dependable choice when compatibility matters most.