OBS Studio – 5.1 AAC in Hybrid MP4 Produces No Audio in VLC

[jmuthu]

Summary​

OBS Studio 32.2.1 (64-bit) on Windows 11 produces a Hybrid MP4 recording with valid 5.1 AAC audio, but the resulting file plays without audio in VLC Media Player 3.0.23.
The same source and 5.1 audio play correctly when:

• recorded as traditional MPEG-4 MP4;
• recorded as MKV;
• the MKV is remuxed to MP4 using FFmpeg with -c copy.

This appears to be a compatibility/interoperability issue involving OBS Hybrid MP4 output and 5.1 AAC audio.

Environment​

• OS: Windows 11 64-bit
• OBS Studio: 32.2.1 (64-bit)
• VLC: 3.0.23 Vetinari
• Laptop: Lenovo IdeaPad 3 15IIL05 (81WE)
• CPU: Intel Core i3-1005G1
• Video encoder: Intel QuickSync H.264
• Audio sample rate: 48 kHz
• Audio source: Desktop audio from a YouTube video
• OBS audio channels: 5.1
• Audio codec: AAC
• OBS Output Mode: Simple for the principal reproduction
• Recording quality: High Quality, Medium File Size

Expected behavior​

A 5.1 AAC recording created by OBS as Hybrid MP4 should play with audio in VLC, just as the same recording does when stored in traditional MP4 or MKV.

Actual behavior​

A 5.1 AAC recording made directly by OBS using Hybrid MP4 plays correctly in Windows Media Player but plays without audio in VLC 3.0.23.
VLC detects the AAC stream, but produces no audible output.

Reproduction steps​

1. Open OBS Studio 32.2.1 (64-bit).
2. Set Settings → Audio → Channels to 5.1.
3. Set Settings → Output → Output Mode to Simple.
4. Set Recording Format to Hybrid MP4 (.mp4).
5. Set Video Encoder to Hardware (QSV, H.264).
6. Set Audio Encoder to AAC (Default).
7. Record a YouTube video containing desktop audio.
8. Stop the recording.
9. Open the resulting MP4 in VLC 3.0.23.
10. Video plays, but there is no audible audio.
11. Open the same MP4 in Windows Media Player.
12. Audio plays correctly.

MediaInfo of affected recording​

The affected MP4 contains a valid 5.1 AAC stream:

• Format: AAC LC
• Bit rate: 192 kb/s
• Channels: 6
• Channel layout: C L R Ls Rs LFE
• Sampling rate: 48.0 kHz
• Codec ID: mp4a-40-2
• Audio: Present and recognized by MediaInfo

Therefore, the recording contains a genuine 5.1 AAC audio stream rather than a missing or corrupt audio track.

Tests performed​

Test 1 – Stereo + Hybrid MP4​

OBS:

• Channels: Stereo
• Output Mode: Simple
• Recording Format: Hybrid MP4
• Video Encoder: Hardware (QSV, H.264)
• Audio Encoder: AAC (Default)

Result:

• Windows Media Player: Audio OK
• VLC: Audio OK

Test 2 – 5.1 + traditional MPEG-4 MP4​

OBS:

• Channels: 5.1
• Output Mode: Simple
• Recording Format: MPEG-4 (.mp4)
• Video Encoder: Hardware (QSV, H.264)
• Audio Encoder: AAC (Default)

Result:

• Windows Media Player: Audio OK
• VLC: Audio OK

Test 3 – 5.1 + MKV​

OBS:

• Channels: 5.1
• Output Mode: Simple
• Recording Format: Matroska Video (.mkv)
• Video Encoder: Hardware (QSV, H.264)
• Audio Encoder: AAC (Default)

Result:

• Windows Media Player: Audio OK
• VLC: Audio OK

The MKV was then remuxed to MP4 using:
ffmpeg -i input.mkv -c copy -movflags +faststart output.mp4
Resulting MP4:

• Windows Media Player: Audio OK
• VLC: Audio OK

Because -c copy was used, the audio and video were not re-encoded.

Test 4 – 5.1 + Hybrid MP4 using FFmpeg AAC​

OBS was changed to Advanced Output Mode and configured as:

• Recording Format: Hybrid MP4
• Video Encoder: QuickSync H.264
• Audio Encoder: FFmpeg AAC
• Channels: 5.1

Result:

• Windows Media Player: Audio OK
• VLC: No audio

Therefore, the problem is not specific to OBS's default AAC encoder.

Test 5 – Remux affected Hybrid MP4 to MKV​

The affected Hybrid MP4 was remuxed with:
ffmpeg -i input.mp4 -c copy test.mkv
Result:

• VLC: Audio OK

No audio or video re-encoding was performed.

Test 6 – Downmix affected 5.1 MP4 to stereo​

The affected MP4 was processed with:
ffmpeg -i input.mp4 -c:v copy -ac 2 testaudio.mp4
Result:

• VLC: Audio OK

This confirms that VLC can decode the resulting AAC audio and that the video itself is not the problem.

Compatibility matrix​

Recording method	Audio
Hybrid MP4	Stereo AAC
Hybrid MP4	5.1 AAC
MPEG-4 MP4	5.1 AAC
MKV	5.1 AAC
MKV → MP4 (-c copy)	5.1 AAC
Hybrid MP4 + FFmpeg AAC	5.1 AAC

[th]

Windows Media Player​

[/th][th]

VLC 3.0.23​

[/th]​

[td]

✅​

[/td][td]

✅​

[/td]​

[td]

✅​

[/td][td]

❌ No audio​

[/td]​

[td]

✅​

[/td][td]

✅​

[/td]​

[td]

✅​

[/td][td]

✅​

[/td]​

[td]

✅​

[/td][td]

✅​

[/td]​

[td]

✅​

[/td][td]

❌ No audio​

[/td]​

Additional observation​

The issue is specific to the direct Hybrid MP4 recording path.
Changing from Hybrid MP4 to traditional MPEG-4 MP4 resolves the VLC problem without changing the video or audio codecs.
Recording to MKV and subsequently remuxing to MP4 with FFmpeg also resolves the problem.
This suggests that the issue may involve the way OBS's Hybrid MP4 muxer writes or describes the 5.1 AAC stream, or an interoperability issue between that output and VLC's MP4 demuxing/channel handling.
I am not asserting that the Hybrid MP4 file is invalid; I am reporting the reproducible interoperability problem and providing working comparison files.

Requested investigation​

Please investigate whether OBS's Hybrid MP4 muxing of 5.1 AAC produces MP4 metadata/channel information that VLC 3.0.23 interprets differently from:

• traditional OBS MPEG-4 output, or
• FFmpeg-generated MP4 output from the same streams.

I am attaching the below files for your reference and comparison:

• Affected 5.1 Hybrid MP4
• Working traditional 5.1 MPEG-4 MP4
• Working 5.1 MKV
• Working 5.1 MKV to FFmpeg-remuxed MP4
• OBS current log upload URL in a TXT file
• FFprobe output of the affected 5.1 Hybrid MP4 in a TXT file

If you can't find the attachments, please use the below link to download the attachments:

OBS Issue – Google Drive

drive.google.com

 

[rockbottom]

When working with surround material, OBS works best with discrete audio. A YT video is not discrete, it's matrixed....

• Audio source: Desktop audio from a YouTube video
• OBS audio channels: 5.1

Surround Sound Guide | OBS

OBS Knowledge Base. Learn how to make streams and recordings with surround sound

obsproject.com

 

[jmuthu]

As the Compatibility Matrix given by me in my original post is scattered, please find below the correct one:

Recording method	Audio	Windows Media Player	VLC 3.0.23
Hybrid MP4	Stereo AAC	✅	✅
Hybrid MP4	5.1 AAC	✅	❌ No audio
MPEG-4 MP4	5.1 AAC	✅	✅
MKV	5.1 AAC	✅	✅
MKV → MP4 (-c copy)	5.1 AAC	✅	✅
Hybrid MP4 + FFmpeg AAC	5.1 AAC	✅	❌ No audio

 

[rockbottom]

Yeah so what? Your source is bogus, matrixed audio will produce mixed results with OBS, read the guide I provided. All of those surround channels must be separate for it to work correctly.

 

[jmuthu]

Yeah so what? Your source is bogus, matrixed audio will produce mixed results with OBS, read the guide I provided. All of those surround channels must be separate for it to work correctly.

Then how does it work correctly with MKV and traditional MPEG-4?

 

[rockbottom]

Surround is compatible with both, also compatible with Quicktime (.mov).

Compatible containers (for recordings):

• mkv
• mp4
• ts
• flv (others untested).

 

[rockbottom]

Without discrete audio, you're better off just recording stereo. Trust me, it's like night & day. I only run discrete for a reason....

 

[rockbottom]

Something else to add, since I'm encoding discrete audio, I encode lossless PCM. No AAC to muddy up the the pristine audio.