Regardless of the original video format, the processed output video will uniformly be in mp4/h264 encoding format. mp4 is a lossy compression format, so any re-encoding will inevitably lead to a change in video quality, regardless of how the configuration is modified.
The following parts of the software involve re-encoding. Whenever these are used, even if crf is set to 0, there will still be some loss of quality.
1. If the original video is not mp4 or not h264 encoded, it will be re-encoded.
This is obvious. Format conversion requires re-encoding, and since mp4 is a lossy format, the quality will definitely be reduced. Additionally, even if the original video is mp4, there is a distinction between h264 and h264 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 the video
Changing the video frame rate will inevitably re-encode the video. If you want to maintain the original quality, you need to disable the use of video slow motion.
3. Selecting to embed hard subtitles will also re-encode the video
Hard subtitles need to be written into the video screen, which naturally requires re-encoding. If you want to maintain the original video quality, you cannot use hard subtitles. You can use soft subtitles instead, but note that soft subtitles cannot be displayed when playing in a web browser, and some playback software requires the soft subtitle file to be renamed to the same name as the video and placed in the same directory in order to be displayed. Some domestic 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 be re-encoded.
After dubbing, the dubbing duration may be longer than the original video. By default, the video will be extended until it matches the dubbing duration. Extending the video requires re-encoding. If you do not want to extend it, uncheck the "Extend video at the end" checkbox in the software interface.
In summary, if you want the video quality to be lossless, you must ensure that:
- The original video is an mp4 encoded with h264.
- Video slow motion is disabled.
- Do not embed subtitles, or only embed soft subtitles. Embedding hard subtitles is prohibited.
- Do not select dubbing, or if dubbing is possible, the "Extend video at the end" option must be disabled.
If the above requirements are not met, but you 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 during video encoding as much as possible.