How to Convert an AVI File to MP4: A Practical Walkthrough
6 min read
What sets this conversion apart from the others
Before you start converting AVI to MP4 you need to set your expectations correctly, because this process works differently from MKV or MOV conversions.
In most MKV or MOV files the video inside is already H.264, and moving to MP4 amounts to nothing more than "changing the box" — fast and without quality loss. With AVI you generally do not get that luck.
AVI files typically contain older codecs such as DivX, Xvid or MPEG-4 Part 2. In practice the MP4 container does not carry these reliably. So going from AVI to MP4 almost always means a genuine re-encode: the picture is decoded and compressed again with H.264.
That has two consequences, and you should start knowing both of them. First, there will be some quality loss — with good settings it is usually not noticeable to the naked eye, but technically it is there and it cannot be undone. Second, the process takes time; on a long file it can run for many minutes.
What to do before you start
Put the original somewhere safe. This is the most important preparation in an AVI conversion. Because the process is lossy, do not delete your source file. If old family videos or archive recordings are involved, you will want to be able to go back to the original when a better method comes along later.
Check the source from start to finish. AVI files, especially ones that have been stored for a long time, may be partly corrupted. Open the file in a player and skip to the middle and to the end. A problem that already exists in the source will not be fixed by the conversion, it will be carried across as is.
Verify the audio sync in the source. AVI's best-known weakness is audio-video drift that accumulates and grows as the minutes pass. Look at the lip sync in the last ten minutes of the film. If the problem is in the source, knowing that up front prevents confusion when you come to judge the result.
If you have subtitles, note where they are. Because AVI does not carry subtitles inside itself, your subtitle is probably a separate .srt file and is unaffected by the conversion.
Step-by-step conversion
1. Upload the file
Open our AVI to MP4 converter and drag and drop the file. Because old AVI files were not compressed with modern codecs they may be larger than you expect; the upload stage can take a while.
2. Wait for the file to be read
At this stage the video and audio codecs inside are detected. If the information is shown on screen, take a look to see which codec you are dealing with.
3. Start the process and be patient
Real compression is happening here. The progress bar may move irregularly; scenes with motion and detail are processed more slowly than static ones. This is normal. Do not interrupt the process, restarting makes it do the work from scratch.
4. Download and compare
Open the new file alongside the original and compare the same scene in both.
Verification after downloading
The checklist for an AVI conversion needs a little more care, because it is a lossy operation.
- Is the duration exactly the same? If there is a difference, the process may have finished incomplete.
- Is the picture quality acceptable? Look at detailed scenes: foliage, crowds, water, fast movement. Blockiness and smearing show up most in those places. Do not make your judgement by looking at a static landscape shot.
- Are audio and video in sync? Do not just check the start, skip to the middle and the end as well.
- Is the audio level normal? In old AVI files a level difference can appear during the audio format conversion.
- Does it open on the new device? That was the whole point; test the file on your television or your phone.
Common problems
The resulting picture is visibly degraded. The bitrate chosen during re-encoding may have been too low. Try again from the same source with a higher bitrate. Do not run the process again on the already-converted MP4 — the losses stack on top of each other.
The video plays but there is no audio. Some old AVI files carry audio codecs that are barely used any more. Make sure the audio track is being encoded to AAC.
The file will not process or throws an error. AVI files stored for a long time may be partly corrupted. Verify whether it opens from start to finish without problems in a player.
The picture is stretched or the proportions are wrong. Old AVI files are sometimes recorded with non-square pixel ratios. If that information is not interpreted correctly during the conversion, the picture comes out flattened or squeezed. You can spot this by comparing the result with the original.
Does changing the extension by hand work? No. AVI's internal structure is completely different from MP4's; turning a .avi extension into .mp4 does not make the file an MP4, it only makes it fail to open.
Advice for archive work
If you have dozens of old AVI files on your hands, try one of them before converting them all and inspect the result carefully. Files that come from the same source have usually been recorded with the same codec and settings; an approach that gives a good result on one will work on the others. Getting the settings right once and only then moving to batch processing is far better than converting fifty files and then realising they all need doing again.
And once more: do not delete the originals. Disk space today is far cheaper than an archive that cannot be brought back.
Conclusion
Moving from AVI to MP4 inevitably involves a trade: you give up some quality and in return you get a smaller, modern file that opens on every device. That trade makes sense in most scenarios, because the quality of a file that will not open is of no practical use at all.
The only thing you need to do is carry out the process deliberately: check the source beforehand, inspect the result on detailed scenes, and keep the originals just in case.
Frequently Asked Questions
Why does this take so much longer than an MKV conversion?
Because the work being done is fundamentally different. With most MKV files only the container is swapped and the data is copied across, which is a fast operation. With AVI, the old codec inside is incompatible with MP4, so the video has to be decoded frame by frame and compressed again with H.264. That is one of the heaviest jobs a computer can be asked to do, and on long files it can take many minutes.
The audio came out drifting against the video, what can I do?
This is a common problem with AVI sources and it usually comes from the source itself. Because the AVI container was not designed to work well with variable bitrate audio, the original file may already have a drift that accumulates and grows as the minutes pass. First open the source AVI in a player, skip to the end and check whether the drift is present there too. If it is in the source, the conversion needs a step that re-times the audio or converts to a constant frame rate.
I had a subtitle file, what happens to it?
Because the AVI container cannot carry subtitles properly inside itself, your subtitle is almost certainly sitting as a separate .srt file. The conversion does not touch that separate file, it stays where it is. If you put your new MP4 in the same folder as the .srt and give both the same name, most players will load the subtitle automatically. If you want the subtitle burned permanently onto the picture, be aware that this is a separate operation and requires re-encoding.
The result file came out smaller than the original, have I lost data?
The drop in size is an expected and normal outcome, and is in fact one of the aims of the conversion. H.264 compresses far more efficiently than the codecs of the AVI era; it can produce the same visual quality with much less data. So the shrinkage is not all loss, most of it is an efficiency gain. Even so, because re-encoding is a lossy operation there is some genuine loss of detail as well, which is why not deleting the original is a good habit.
Try this out right away with AVI → MP4 Dönüştür.
Try AVI → MP4 Dönüştür