fix(video): correct codec option strings to the key=value form

parse_options reads : and , as separators and = as the only assignment, so a
segment without = becomes a valueless flag set to 1. The shipped strings used
ffmpeg command line spelling, which parses without error into other values.

- crf:16 parsed to {'crf': '1', '16': '1'}, encoding every api, framepack and
  seedvr video near lossless rather than at crf 16
- crf=23:b:v=0 pinned the generic bitrate option to 1 bit per second on vp8 and
  vp9, collapsing their output
- qscale:v=3 reached mpeg4 and mjpeg as nothing at all, replaced by an explicit
  quantizer range
- test-video-codecs.py asserts every preset segment carries an assignment

modules/api/video.py

@@ -38,7 +38,7 @@ class ReqVideo(BaseModel):
     mp4_interpolate: int = Field(default=0, ge=0, le=10, title="Interpolation", description="RIFE interpolation passes between frames")
     mp4_codec: str = Field(default="libx264", title="Codec", description="Video codec; none skips video encoding")
     mp4_ext: str = Field(default="mp4", title="Container", description="Container extension; the muxer is inferred from it")
-    mp4_opt: str = Field(default="crf:16", title="Codec options", description="Encoder options as comma-separated key:value pairs")
+    mp4_opt: str = Field(default="crf=16", title="Codec options", description="Encoder options as key=value pairs separated by : or ,")
     mp4_video: bool = Field(default=True, title="Save video", description="Write the video container to disk")
     mp4_frames: bool = Field(default=False, title="Save frames", description="Write individual frame images to disk")
     mp4_sf: bool = Field(default=False, title="Save safetensors", description="Write raw frames as a safetensors file")