Regardless of the original video format, the output video is uniformly processed to mp4/h264 encoding format. Since mp4 is a lossy compression format, any re-encoding will inevitably alter video quality, no matter how the settings are adjusted.
The following sections involve re-encoding in the software. If used, even setting crf to 0 will result in some quality loss.
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 inevitably decrease. Additionally, even if the original video is in 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 with h264 encoding.
If you have PotPlayer installed, you can right-click on the video playback screen and select "Properties" to check the specific encoding method.
2. Re-encoding When Enabling Video Slow Motion
Changing the video frame rate necessarily requires re-encoding. To maintain original quality, avoid using video slow motion.
3. Re-encoding When Choosing to Embed Hard Subtitles
Hard subtitles need to be written into the video frames, which naturally requires re-encoding. To preserve original video quality, do not use hard subtitles. Instead, use soft subtitles. However, note that soft subtitles may not display in web players, and some playback software requires the soft subtitle file to be renamed to match the video file and placed in the same directory. Some Chinese players may also require manually converting the srt file to GBK encoding.
4. Re-encoding if the Video End is Extended
After dubbing, the audio duration may exceed the original video length. By default, the video is 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 End" option in the software interface.
Summary: To Ensure No Loss in Video Quality, You Must
- Ensure the original video is an mp4 with h264 encoding.
- Disable video slow motion.
- Do not embed subtitles or only use soft subtitles; avoid embedding hard subtitles.
- Do not select dubbing, or if dubbing is used, disable video end extension.
If the above requirements are not met but you still want to maintain the highest possible video quality, you can change crf=13 to crf=0 in the advanced options to minimize quality loss during encoding.