No matter the original video format, the processed output video will be in MP4/H.264 encoding format. MP4 is a lossy compression format, so any re-encoding will inevitably change the video quality, regardless of configuration changes.
The following parts of the software involve re-encoding. Using any of these, even setting crf to 0, will result in some quality loss.
1. Original Video is Not MP4 or Not H.264 Encoded, Will Re-encode
This is obvious. Format conversion requires re-encoding, and since MP4 is a lossy format, the quality will definitely decrease. Also, even if the original video is MP4, it distinguishes between h264 and H.264 encoding. h264 is a more compatible encoding method, so the output will use h264.
If you want to maintain the original video quality, you must first ensure that the original video is an MP4 video in h264 format.
If you have PotPlayer installed, you can right-click "Properties" on the video playback interface to view the specific encoding method.
2. Enabling Video Slow Motion Will Re-encode
Changing the video frame rate will inevitably re-encode. If you want to maintain the original quality, you need to disable video slow motion.
3. Selecting to Embed Hard Subtitles Will Also Re-encode
Hard subtitles need to be written into the video frame, which naturally requires re-encoding. If you want to maintain the original video quality, you cannot use hard subtitles. You can use soft subtitles, but note that soft subtitles cannot be displayed when playing in a web browser. Also, some playback software requires renaming the soft subtitle file to be the same name as the video and placing it in the same directory for it to be displayed. Some Chinese media players may also require manually converting the SRT file to GBK encoding.
4. If There is an Extension at the End of the Video, It Will Also Re-encode
After voice-over, the voice-over duration may be longer than the original video. By default, the video will be extended to match the voice-over duration. Extending the video requires re-encoding. If you don't want to extend it, uncheck the "Video End Extension" checkbox in the software interface.
In Summary, If You Want the Video Quality to Have No Loss, You Must Ensure:
- The original video is an MP4 encoded with h264.
- Disable video slow motion.
- Do not embed subtitles or only embed soft subtitles; prohibit embedding hard subtitles.
- Do not select voice-over, or if voice-over is enabled, you must also prohibit video end extension.
If you do not meet the above requirements, but still want the video to maintain the highest possible quality, you can change crf=13 to crf=0 in the advanced options. This will minimize the quality loss in video encoding.