I am talking about spatial compression.
To get the correct aspect ratio again, I have to stretch it in the player.
That works, of course. But it's annoying in the long run.
I haven't experienced this issue before. I'm also using MPC-HC.
I will try to run a test encoding later.
Well ... usually black bars use VERY little space, because the information can be described as two rectangles with one colour, which can be saved with only some bytes.
Of course it's a bit more difficult, but the size should be less than 1% of the picture size.
20% difference is a bit strange though.
I understand your point about the compression of uniform areas like black bars. They can be highly efficient and require minimal data to represent them due to their uniformity. The compression algorithms, especially in advanced codecs like HEVC, are pretty effective at minimizing the space these uniform sections occupy.
However, there are other factors to consider beyond just the space taken by the black bars themselves. Cropping black bars before encoding can change the overall dynamics of video compression. When these bars are removed, the encoder can allocate more of its available bitrate to the actual content, potentially enhancing the quality of the visible parts of the video. Alternatively, it can maintain the same quality with a lower bitrate, thus reducing the file size.
The impact on file size can vary significantly depending on the content's complexity, motion, and the chosen bitrate for encoding. In static or less complex scenes, the difference might indeed be minimal. But in more dynamic or detailed content, the efficiency gains from reallocating bitrate to actual content instead of black bars can be more pronounced.
So, while the direct impact of black bars on file size might be small due to efficient compression, the indirect effects on the encoding process and bitrate distribution can lead to noticeable differences in specific scenarios. A 10-25% figure might be on the higher side and more typical for cases where black bars take up a substantial portion of the frame and the content benefits significantly from bitrate reallocation post-cropping.
A quick test run with Indiana Jones and cropping black bars reduces file size by ca 12.30%.