This video can't be played

[levicki]

• I have searched open and closed issues for duplicates
• I am submitting a bug report for existing functionality that does not work as intended
• This isn't a feature request or a discussion topic

---

Bug description

Video of an app window recorded on a Windows PC using OBS fails to play on IOS (works on PC and Android).

Video encoding details:

General
Complete name                            : D:\Recordings\2026-08-06 13-46-40.mp4
Format                                   : MPEG-4
Format profile                           : Base Media
Codec ID                                 : isom (isom/iso2/mp41)
File size                                : 3.07 MiB
Duration                                 : 27 s 350 ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 943 kb/s
Writing application                      : Lavf62.12.102

Video
ID                                       : 1
Format                                   : HEVC
Format/Info                              : High Efficiency Video Coding
Format profile                           : Main@L3.1@Main
Codec ID                                 : hev1
Codec ID/Info                            : High Efficiency Video Coding
Duration                                 : 27 s 350 ms
Source duration                          : 27 s 300 ms
Bit rate                                 : 886 kb/s
Maximum bit rate                         : 10 000 kb/s
Width                                    : 804 pixels
Height                                   : 478 pixels
Display aspect ratio                     : 5:3
Frame rate mode                          : Constant
Frame rate                               : 60.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Bits/(Pixel*Frame)                       : 0.038
Stream size                              : 2.89 MiB (94%)
Source stream size                       : 2.99 MiB (97%)
Color range                              : Full
Color primaries                          : BT.709
Transfer characteristics                 : sRGB/sYCC
Matrix coefficients                      : BT.709
mdhd_Duration                            : 27367
Codec configuration box                  : hvcC

Audio #1
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 27 s 264 ms
Source duration                          : 27 s 285 ms
Bit rate mode                            : Variable
Bit rate                                 : 2 274 b/s
Maximum bit rate                         : 256 kb/s / 256 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 7.57 KiB (0%)
Source stream size                       : 7.58 KiB (0%)
Title                                    : Desktop Audio
Default                                  : Yes
Alternate group                          : 1

Audio #2
ID                                       : 3
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 27 s 264 ms
Source duration                          : 27 s 285 ms
Bit rate mode                            : Variable
Bit rate                                 : 2 274 b/s
Maximum bit rate                         : 256 kb/s / 256 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 7.57 KiB (0%)
Source stream size                       : 7.58 KiB (0%)
Title                                    : VOIP Audio
Default                                  : No
Alternate group                          : 1

Audio #3
ID                                       : 4
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 27 s 264 ms
Source duration                          : 27 s 285 ms
Bit rate mode                            : Variable
Bit rate                                 : 2 274 b/s
Maximum bit rate                         : 256 kb/s / 256 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 7.57 KiB (0%)
Source stream size                       : 7.58 KiB (0%)
Title                                    : MIC Audio
Default                                  : No
Alternate group                          : 1

Steps to reproduce

• Record a video with settings like the ones above
• Share it with yourself from Windows PC Signal version
• Try playing it on IOS Signal app

Actual result: Video displays a square with play symbol and a slash drawn over it. Tapping it shows the message "This video can't be played" at the bottom of the app window.

Expected result: Video should display preview and play normally.

Screenshots

Device info

Device: iPhone 16 Pro Max

iOS version: 26.6

Signal version: 8.22 (1774)

Link to debug log

[levicki]

I tried also without audio channels, it seems that the video stream itself is the problem.

EDIT: Yes, video stream is the "problem".

Codec ID (hev1 vs hvc1)
iOS devices, Apple's AVPlayer, and apps using AVFoundation often refuse to play HEVC videos with the hev1 tag. Apple strictly requires the hvc1 codec tag for hardware acceleration and native playback.

In my test a simple ffmpeg -i input.mp4 -c:a copy -c:v copy -tag:v hvc1 output.mp4 fixes it and makes it playable.

Possible workarounds in app would be to inspect FOURCC and swap it before passing to AVFoundation (if that's what you use) or to use VLCKit or something similar to play media without IOS format restrictions.

[milan-signal]

Pozdrav, Igore - davnih dana smo se upoznali na ES.org u vreme dok si primio nagradu od Intela.

Taking the case under the investigation. Stay tuned.

[milan-signal]

@levicki - even though the issue seems to be strictly caused by just the one described detail ('hev1' vs. 'hvc'1),
if there is any chance to upload a zipped unmodified file which causes the problem to

support@signal.org

CORRECTION: support-attachment@signal.org

with the message 'send this to the media team as requested', it would definitely establish the common ground for the troubleshooting session and eliminate any misunderstanding down the road.

Your help is much appreciated !

[levicki]

Zdravo Milane, secam se.

Daj mi par minuta dobices video ovde (napravicu novi uzorak).

[levicki]

@milan-signal

FOURCC: HEV1 (unplayable on IOS, works on Android and Windows PC)

FOURCC_HEV1.mp4

FOURCC: HVC1 (works fine everywhere)

FOURCC_HVC1.mp4

Both files in a ZIP just in case GitHub decided to transcode them:
Recordings.zip

Hope it helps.

[milan-signal]

Great ! Thanks a whole lot !

Will post the updates hopefully some time soon

[milan-signal]

The findings after careful analysis of the problem && examination of the current Signal media handling infrastructure:

• the full and absolutely correct replacement of 'hev1' with 'hvc1` box is not a trivial measure

More details:

• as it is fairly easy to rename the 'hev1' box into the 'hvc1', there remains a general problem about the contents of their 'daughter' hvcC boxes:
• In the case of 'hvc1', the 'hvcC' box is mandated to carry absolutely every VPS/SPS/PPS tuple used by the H.265 stream
• In the case of 'hev1', the contents of 'hvcC' box, this criterion is not as firm. In fact, the bitstream itself (stored in the 'mdat' box) may carry arbitrary number of different VPS/SPS/PPS tuples undeclared in the 'hvcC' box

The absolutely satisfactory solution would require scanning the entire stored H.265 stream, capturing all encountered VPS/SPS/PPS tuples, and upgrading the 'hvcC' box contents with the full set of them.

Given that the 'hev1' imposes greater flexibility of the media stack and decoder, which comes at the cost of design complexity and increased security attack surface, it is no wonder that Apple mandates the use of 'hvc1' box.

it has been determined that the current Signal media handling stack does not have immediately available and easily adaptable framework for the thorough solution for this problem.

The presence of the issue is duly acknowledged by the Signal development team && there is a good will to provide the solution for it. However, it will not happen until a major media stack code releases in the the future.

In the meantime, the users are strongly suggested to rely on the simple ffmpeg transformation mentioned above by the issue author.

[levicki]

The presence of the issue is duly acknowledged by the Signal development team

In that case let me tell you my opinion on the subject — if Signal's security model or player constraints prevent them from playing hev1 natively, the app should at least handle the failure gracefully:

• Clear Error Messaging: Inform the user why it can't play (e.g., "Unsupported video format : HEV1") instead of showing a generic "This video can't be played".

• Fallback Options: Provide a "Save to Files / Share" button to open the video using an external player (like VLC) or app (like FE File Explorer with built-in custom player) or one of myriad of remuxing or transcoding apps which can usually handle formats not natively supported by Apple hardware accelerated codecs.

Leaving non-technical users completely stranded with an unplayable file which they can't even take out of Signal to try other options and telling them to remux it via CLI is a classic example of developer reasoning overriding user experience.