+ Potential fields:
+ * url Mandatory. The URL of the video file
+ * ext Will be calculated from url if missing
+ * format A human-readable description of the format
+ ("mp4 container with h264/opus").
+ Calculated from the format_id, width, height.
+ and format_note fields if missing.
+ * format_id A short description of the format
+ ("mp4_h264_opus" or "19")
+ * format_note Additional info about the format
+ ("3D" or "DASH video")
+ * width Width of the video, if known
+ * height Height of the video, if known
+ * resolution Textual description of width and height
+ * abr Average audio bitrate in KBit/s
+ * acodec Name of the audio codec in use
+ * vbr Average video bitrate in KBit/s
+ * vcodec Name of the video codec in use
+ * filesize The number of bytes, if known in advance
+ * player_url SWF Player URL (used for rtmpdump).
+ * preference Order number of this format. If this field is
+ present, the formats get sorted by this field.
+ -1 for default (order by other properties),
+ -2 or smaller for less than default.
+ url: Final video URL.
+ ext: Video filename extension.