MP4 holds picture and sound; MP3 holds audio
MP4 is a container that can hold video and audio together. A screen recording, camera clip, or exported lesson may use it, but the extension does not tell you which audio codec is inside. MP3 stores compressed audio without the picture. Converting a video to MP3 gives you a listening copy for reviewing a conversation or sharing a narration take. It keeps sounds mixed into the soundtrack, so speech, music, and room noise are not separated into individual files.
Choose bitrate for the listening copy
The MP3 choices are 128, 192, and 320 kbps. Bitrate is the amount of data used per second of audio, so a longer recording needs more space at the same setting. Start with the default 192 kbps and listen to speech, music, and quiet passages before deciding whether to change it. A higher setting gives compressed audio more data, but it cannot recover detail already lost in the recording. Choose WAV instead when your next editor needs uncompressed audio.
Extraction leaves the picture behind
The converter excludes video from the output and asks for MP3 audio at your chosen bitrate, or writes a WAV when selected. Audio in another codec must be decoded and converted to the output format. This is not a way to improve the source recording or remove noise. The original video remains available because the result is a separate download. Listen to that result before using it in a transcript workflow, especially if the original contains long silences or several speakers.
Check the source before trying again
A video needs a readable audio track before there is anything to extract. A silent screen recording cannot produce missing speech, and a familiar filename does not guarantee that its codec is supported. If conversion fails, first check whether the original contains sound and plays correctly. Try a source with audio your browser supports. Large files also need room in device memory, so a shorter recording can be a more practical starting point when the browser cannot finish the job.
