Music Ends Before Your Video? Fix the Length

Your video and your track are two separate streams with two separate lengths, and whatever combines them has to decide which length wins. That decision is the whole problem. A tool that ends the output when either stream runs out will chop your video at the last second of the song. A tool that runs until the longer stream ends will hold the picture or leave a tail of dead air. Neither is a bug, it is a default nobody told you about. In pixeltools' Add Audio to Video tool the choice is an explicit control called Length, with three options: Video, Shortest and Loop. Pick the one that matches what you want the finished file to be, and the result is predictable every time.

Video mode keeps every frame of the picture no matter how long the track is, and it is the default. If your song is shorter than the clip, the rest of the video plays in silence after the song ends. If your song is longer, it stops at the last frame of the video instead of dragging on. Nothing about the picture's duration ever changes. This is the right choice for a voiceover that ends before the footage does, a single song over a longer clip where you want a quiet ending, or any case where the video is the fixed thing and the audio must fit it. If you hear silence at the end and it bothers you, that is the signal to switch to Loop, not to a different tool.

Shortest mode ends the file the moment either the video or the track runs out, so a 30-second song on a 2-minute clip gives you a 30-second video. That is exactly what it promises, and it is the usual reason for the complaint "adding music made my video shorter." It is useful in one situation: you have a track and a clip and want the output to be as long as the smaller of the two, for example trimming a long video down to a short jingle. If you did not want that, switch back to Video or Loop and export again. The original files are never modified, so trying another mode costs you nothing but a re-run.

Loop mode restarts your track from the top as many times as it takes to reach the last frame, then stops there, so the video keeps its full length and never falls silent. Two limits are worth knowing. The restart is a hard cut back to the first sample, with no crossfade, so a track that does not begin and end on the same beat will show a seam at each repeat. And the final repeat is cut wherever the video ends, mid-phrase if that is where it lands. If the seam bothers you, trim the track to a clean bar length first with the Trim Audio tool so the loop point lands on a beat, then add it.

The tool copies your video stream as-is and only encodes the audio, as AAC at 192 kbps in an MP4. That has two consequences. First, there is no quality loss on the picture. Second, the video length cannot be stretched: no mode makes a video longer than it already is, so a 10-second clip with a 3-minute song is a 10-second file. The one exception is a source MP4 cannot hold as-is, such as VP9 from a WebM. In that case the tool retries by re-encoding the picture with H.264 (CRF 23), which is slower but still keeps the same duration.

Replace drops the video's own sound and keeps only your track. Mix lays your track over the original audio and keeps both audible. The volume slider only affects the added track, from 0 to 200 percent, and 200 percent is +6 dB. Mix does not turn the original down for you, so pick a lower percentage if your music competes with dialogue. If the source video has no audio at all, such as a screen recording, there is nothing to mix with. The tool detects this before it runs, adds your track on its own exactly as Replace would, and the result screen says so instead of presenting a lone track as a mix.