Regardless of the original video format, the processed output video will be uniformly in the mp4/h264 encoding format. Since mp4 is a lossy compression format, any re-encoding will inevitably alter the video quality, no matter how the settings are adjusted.
The parts of the software that involve re-encoding are listed below. If any of these are used, there will be some loss in quality, even if the crf is set to 0.
1. Re-encoding if the original video is not mp4 or not h264 encoded
This is obvious. Format conversion requires re-encoding, and since mp4 is a lossy format, quality will certainly decrease. Additionally, even if the original video is mp4, it may use different encodings like h264 or h265. H264 offers better compatibility, so the output will use h264.
If you wish to preserve the original video quality, you must first ensure that the original video is an mp4 video encoded with h264.
If you have PotPlayer installed, you can right-click on the video playback screen and select "Properties" to view the specific encoding method.
2. Enabling video slow motion will trigger re-encoding
Changing the video frame rate necessarily requires re-encoding. If you want to maintain the original quality, you need to avoid using video slow motion.
3. Choosing to embed hard subtitles will also trigger re-encoding
Hard subtitles need to be written into the video frames, which naturally requires re-encoding. To preserve the original video quality, do not use hard subtitles. You can use soft subtitles instead. However, note that soft subtitles cannot be displayed during web playback. Also, some playback software requires the soft subtitle file to be renamed to match the video file name and placed in the same directory for display. Some Chinese media players might also require manually converting the SRT file to GBK encoding.
4. If the video is extended at the end, it will also trigger re-encoding
After dubbing, the audio duration might be longer than the original video. By default, the video will be extended to match the dubbing duration. Extending the video requires re-encoding. If you do not want to extend the video, uncheck the "Extend video at end" option in the software interface.
Summary: To ensure no loss in video quality, you must ensure that:
- The original video is an mp4 encoded with h264.
- Video slow motion is disabled.
- No subtitles are embedded, or only soft subtitles are used. Embedding hard subtitles is prohibited.
- Dubbing is not selected, or if dubbing is used, you must simultaneously disable video extension at the end.
If the above requirements are not met, but you still wish to maintain the highest possible video quality, you can change crf=13 to crf=0 in the advanced options. This will minimize quality loss during encoding.