For one local MP4, add it as an OBS Media Source and enable Loop in the source properties. That makes OBS replay the file after it finishes; it does not repair faulty timestamps or audio and video that are already out of sync.
Before you re-encode a long file, find out whether the problem is present in the MP4, appears only in OBS, accumulates over time, or happens at the loop boundary. Those symptoms point to different checks, and changing settings without distinguishing them can make a sound file harder to diagnose.
What OBS looping does—and does not do
OBS’s Media Source plays an individual media file. Its Loop option starts playback again when the file reaches its end. OBS lists MP4 as a supported format, but the loop control is a playback setting, not a timing-repair tool. It does not promise to rewrite timestamps, convert variable frame timing to constant frame timing, or synchronise an audio track that is drifting.
The distinction matters because a file can replay normally while carrying a timing problem. If audio is gradually further ahead of the picture near the end than it was near the beginning, enabling Loop merely brings the file back to its start after that playback. If the first frame and last frame do not join cleanly, the repeat may produce a visible jump or audible click even when audio and picture remain synchronised throughout the clip.
Start by describing the symptom rather than labelling it “drift”. Note when it begins, whether the offset grows, whether it resets on replay, and whether you hear or see a problem only at the seam. You can use a simple written log: “in sync at start, audio ahead near end” is more useful than “OBS broken”.
A looped devotional video, for example, might have a continuous tanpura bed with a final reverberation that is cut off when the first frame starts again. That is a boundary issue, not necessarily accumulated audio/video drift. For broader context on keeping a continuous broadcast running, see this guide to setting up a 24/7 Telugu bhajan stream in OBS.
Add a local file with Media Source
For a single file on the computer running OBS, add a Media Source to the scene. Give it a name that identifies the content if the scene has several sources, then select the MP4 in the source properties. The exact wording and placement of controls can vary between OBS versions, so use the current OBS interface rather than relying on a screenshot from an older release.
A Media Source is the straightforward path when there is one file and you want it to repeat. Keep the file in a stable folder rather than moving or renaming it after selecting it. If OBS can no longer find the media at its saved path, the source cannot play that file. Avoid editing the only copy of a long programme while you are testing; duplicate it first if you intend to change or convert it.
If the MP4 includes more than one audio track, check which track the source is actually playing and whether that is the intended language or mix. Do not assume a timing problem until you have ruled out selecting the wrong track or hearing an additional copy of the audio elsewhere in the scene. A second source playing the same soundtrack can sound like echo or a timing offset even when the MP4 itself is fine.
OBS’s Media Sources documentation describes the source controls and supported playback behaviours. Use it as the reference for the current option names. The practical point is simple: set up the media source first, then test playback with the rest of the scene arranged as it will be used.
Enable Loop and test playback
In the Media Source properties, enable Loop, then start playback from the beginning. Listen and watch at several points: near the opening, somewhere in the middle, towards the end, and across the transition back to the start. If the source is long, note timestamps or scene-clock readings so you can compare the same passage on another run.
Test in the actual OBS scene, not only in a separate media player. Scene filters, audio monitoring, other sources, and the way the scene is routed can affect what you hear. For diagnosis, keep the scene simple: temporarily mute unrelated audio sources, confirm the MP4’s own sound, and then restore the normal scene to see whether the issue returns.
A short preview that stops before the file’s end cannot tell you how the loop seam behaves. Let the source reach the end at least once. If the symptom only appears after several complete plays, keep the test running long enough to observe that pattern rather than concluding that one clean transition proves the setup.
Do not make several changes between tests. If you change the source, audio settings, and the MP4 at the same time, you lose the ability to tell which change mattered. Record the original state, test one change, and compare the result under the same conditions. The aim is not to establish that every long MP4 will play perfectly; it is to locate where the fault enters the chain.
When a VLC Video playlist is more appropriate
A VLC Video source is useful when you need OBS to play a playlist rather than repeat one file. OBS documents playlist controls, including Loop Playlist, for that source. It depends on VLC being installed, and OBS notes that a 64-bit OBS installation requires 64-bit VLC. For a single MP4, Media Source avoids that additional dependency.
| Playback need | Source to consider | What to check |
|---|---|---|
| Repeat one local MP4 | Media Source with Loop enabled | The file’s sync and the transition from its end to its start |
| Play several files in sequence | VLC Video source with a playlist | VLC installation and matching 32- or 64-bit architecture |
| Select among multiple audio tracks or playlist behaviours | Check the source controls for the chosen approach | Which track is audible and whether the intended item order is preserved |
Use the VLC source because you need its playlist behaviour, not as a speculative fix for drift. Switching source types may change how items and tracks are selected, but it does not establish that a faulty MP4 has been repaired. If the same file is out of sync in another player and in OBS, investigate the file before rebuilding a playlist around it.
For readers managing a set of clips, playlist maintenance is a separate task from timing repair. This article on keeping an OBS playlist in sync after replacing files addresses the risk of a playlist referring to changed media; it is not a remedy for timestamps inside an individual video.
Check whether the drift repeats or accumulates
First play the MP4 outside OBS in a player you already use. Check a recognisable event where the sound and picture should coincide near the beginning, then check another near the middle and near the end. Also inspect the intended loop transition. This is a diagnostic comparison, not a certification that the file will behave identically in every playback application.
If the same growing offset appears outside OBS, the evidence points towards the file or its encoded streams rather than the OBS Loop checkbox. If it plays in sync elsewhere but not in the OBS scene, look at the source setup, other active audio, and audio-device configuration before converting the file. If the offset is roughly the same throughout, you may be hearing a fixed offset rather than cumulative drift.
A seam problem has a different shape. A click, a brief silence, a jump in the picture, or a cut-off syllable exactly when playback restarts can result from the content at the file’s endpoints. Compare the final audio and video with the first moments. A loop is only as smooth as those endpoints; no playback setting can make unrelated ending and opening material continuous.
For a gradual change in sync, check whether OBS and the relevant audio devices use compatible sample-rate settings. OBS community discussions include sample-rate mismatch as a diagnostic clue, but that does not show that every drifting file has this cause or that changing the setting will correct an already encoded file. Test the setting in a controlled way and retest the same passage. If you are diagnosing a broadcast as well as local playback, keep network symptoms separate: buffering and upload jitter on a 24/7 stream are not the same thing as audio/video timing within an MP4.
Inspect file timing before re-encoding
Before conversion, identify what you know about the source: its codec and frame timing, whether the audio and video are separate streams, whether the issue appears outside OBS, and whether the offset grows or is constant. If you do not know those details, avoid choosing a target frame rate just because it is a familiar number. A rate that does not match the source may require frames to be duplicated or dropped.
Do not confuse bitrate with frame timing. CBR and VBR describe constant or variable bitrate; CFR and VFR describe constant or variable frame rate. OBS forum administrator, moderator, and developer RytoEX makes the distinction directly in a discussion about variable frame rate: “CBR (Constant BitRate) vs. VBR (Variable BitRate) has nothing to do with CFR (Constant Frame Rate) vs. VFR (Variable Frame Rate).” A file labelled CBR is not thereby proven to have constant frame timing.
If you are considering a container change, separate remuxing from transcoding. A remux changes the container while copying the encoded streams; it does not normally re-encode the video or audio. FFmpeg documents stream copy with -c copy in its official documentation. Copying streams avoids a transcode, but it is not a general timing repair: the outcome still depends on the source streams, timestamps, and options used.
A conversion that conforms output to a chosen constant frame rate is different. FFmpeg’s documentation describes output frame-rate modes that can duplicate or drop frames to meet the selected rate. That changes the video stream and may affect motion or timing. Do not apply a guessed rate as a universal cure, and do not copy an unverified command from a forum into a valuable long recording. The appropriate conversion depends on details not visible from the filename alone.
The goal of inspection is to decide whether a conversion is justified and what it should address. A remux may be worth investigating when the container or timestamp handling is implicated, but it should not be described as equivalent to making variable timing constant. A transcode may be necessary for a specific compatibility or frame-timing objective, but it can take time and alter the output. Keep the original until the converted copy has passed the same checks as the source.
Retest the prepared file in OBS
If you have made a copy through a remux or a deliberate transcode, test that copy outside OBS first. Compare audio and picture near the beginning, middle, end, and loop seam using the same passages you checked in the original. This provides a direct comparison rather than relying on memory of whether one version “felt better”.
Then replace the file in the OBS Media Source only for the test, enable Loop, and run the source through a complete transition. Check that the intended audio track is present, that the scene does not duplicate sound, and that the change has not introduced a new offset or boundary click. If the file is part of a playlist, verify item order and the transition between the actual adjacent items as well.
Keep both versions until the result is verified. If the converted file is worse or has a different fault, return to the original and reconsider the diagnosis rather than layering more changes on top. There is no universal repair command established for every long MP4, and the available OBS guidance on looping does not promise drift-free playback for an arbitrary file.
If the aim is an always-on YouTube channel and leaving the computer running is itself the operational problem, StreamNeo can remove the need to keep that computer on after you have prepared the media: it turns an uploaded video into a YouTube live stream, with your own computer switched off. That addresses the continuous-running burden; it does not replace checking that the file itself is in sync.
For a broader comparison of the workload involved in keeping a channel live, see cloud streaming versus a spare PC.
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FAQ
Does enabling Loop fix audio drift in an MP4?
No. Loop tells OBS to start the file again when playback finishes; it does not repair timestamps or synchronise streams inside the file. Diagnose whether the offset is present outside OBS and whether it grows over time before changing the media.
Should I use Media Source or VLC Video for one MP4?
For one local file, Media Source with Loop is the simpler built-in choice. VLC Video is more appropriate when you need a playlist and its playback controls, and it requires VLC installed with an architecture compatible with OBS.
Does CBR mean my file has a constant frame rate?
No. CBR concerns bitrate, while CFR concerns frame timing. A bitrate label alone does not establish whether frames are spaced uniformly.
Should I convert every long MP4 before looping it?
No. First test the existing file outside OBS and in the actual OBS scene, including the end-to-start transition. Convert only when you have a specific issue to address, and compare the prepared copy at several points before replacing the original.