I am assuming this is caused by TMH having problems with vbr mode but if I am wrong please change the project...
Looking at the metadata of some video file and reading the video stream bitrate, the API returns a negative value: https://commons.wikimedia.org/w/api.php?action=query&prop=imageinfo&format=xml&iiprop=metadata&titles=File%3A%D8%AC%20in%20various%20positions..webm
The total bitrate can be calculated via https://commons.wikimedia.org/w/api.php?action=query&prop=videoinfo&format=xml&viprop=size&titles=File%3A%D8%AC%20in%20various%20positions..webm
I am unsure where the negative bitrate comes from but I am assuming TMH's logic is buggy, which may or may not work this way:
video_bitrate = total_bitrate - audio_bitrate
above example:
video_bitrate = 53.6 kbps - 112 kbps = -58.4 kbps