To convert FLV to a modern video format like MP4 without losing quality, you must use a process called remuxing (stream copying) instead of re-encoding. The Secret to Lossless Conversion: Remuxing
Video files consist of two main parts: the codec (the actual compressed video/audio data) and the container (the box holding the data, like .flv or .mp4).
Re-encoding decompresses and recompresses the video, which takes time and causes a permanent loss of visual quality.
Remuxing strips away the old .flv box and places the original, untouched video stream directly into a modern .mp4 box. This process takes only a few seconds, uses minimal CPU, and preserves 100% of the original quality.
Note: Remuxing works perfectly if your FLV file contains H.264 video and AAC audio codecs, which is true for most modern FLV files. If it uses legacy Flash codecs (like Sorenson Spark or NellyMoser), you must re-encode it. Method 1: The Fastest Lossless Method (Using FFmpeg)
FFmpeg is a free, command-line tool that allows you to change video containers instantly without touching the internal video quality. Download and open FFmpeg on your computer.
Open your terminal or Command Prompt in the folder where your video is located. Run the following command: ffmpeg -i input.flv -c copy output.mp4 Use code with caution.
The -c copy flag tells the software to copy the audio and video streams exactly as they are, achieving an instant, lossless conversion. Method 2: The Best Free GUI Software (Using OBS Studio)
If you already use OBS Studio for recording or streaming, it has a brilliant built-in lossless remuxer. Open OBS Studio.
Click on File in the top menu bar, then select Remux Recordings. Drag and drop your .flv file into the OBS Recording column. The target file will automatically fill in as an .mp4 file.
Click the Remux button at the bottom. The conversion will complete almost instantly with zero quality degradation. Method 3: When Re-Encoding is Required (Using HandBrake)
FFMPEG convert flv to mp4 without losing quality – Super User
would you know a way to make a script for batch conversion of many videos in the same folder ? ttoine. – ttoine. 2015-07-08 09:05: Super User
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