When a video is uploaded to a major platform, it is transcoded into multiple "format codes" to support Dynamic Adaptive Streaming over HTTP (DASH). Format 134 is a standardized identifier for a specific set of technical specifications:
yt-dlp -f 134 [URL] will fetch the 360p video-only file. 134 mp4
Typically 640x360 or 480x360, commonly known as 360p . Codec: Uses AVC1 (H.264) , specifically profile avc1.4d401e . When a video is uploaded to a major