Can a VOB File Have Multiple Aspect Ratios?

A single VOB (Video Object) file can technically contain both 4:3 and 16:9 aspect ratio content in sequence, but standard DVD playback specifications strictly discourage or prevent it. While the underlying MPEG-2 video stream allows aspect ratio changes at sequence headers, DVD-Video standards require a single Video Title Set (VTS) to maintain a uniform display aspect ratio. As a result, how this content behaves depends entirely on whether it is played as a standalone digital file or as part of an authored DVD.

The Underlying MPEG-2 Technical Reality

A VOB file is fundamentally an MPEG-2 Program Stream containing multiplexed video, audio, and subtitle tracks. At the stream level, MPEG-2 allows new Sequence Headers to appear periodically. Each Sequence Header carries display aspect ratio (DAR) metadata, which can switch between 4:3 and 16:9.

If you concatenate two MPEG-2 video streams with different aspect ratios into a single .vob file, the file remains technically valid at the bitstream level. Modern software media players like VLC, MPC-HC, or MPV read these inline headers dynamically and can adjust the display window or output aspect ratio on the fly when the transition occurs.

DVD-Video Specification Restrictions

While standalone media players can handle inline aspect ratio switches, the official DVD-Video specification operates differently. When authoring a DVD:

1. IFO Files Dictate Display Settings: A DVD player does not inspect the VOB video headers to determine the aspect ratio. Instead, it reads the .IFO file associated with the Video Title Set (VTS). The IFO file declares the aspect ratio for the entire VTS up front.
2. Fixed Format per Title Set: An authoring tool sets the aspect ratio attribute for an entire VTS as either 4:3 or 16:9. A single VTS cannot be marked as both.
3. Player Disruption: If a VOB with changing aspect ratios is forced onto a standard DVD within the same title, standalone DVD players will stick to the aspect ratio declared in the IFO file. This forces the secondary ratio to stretch or squash, or in some hardware players, causes decoding errors, video freezing, or distorted video output.

How DVD Standards Handle Mixed Aspect Ratios

To properly display both 4:3 and 16:9 content on a standard DVD without distortion, the content must be authored using one of two standard approaches:

• Separate Video Title Sets (VTS): The 4:3 content is authored into one VTS (e.g., VTS_01_*.VOB), and the 16:9 content is authored into another (e.g., VTS_02_*.VOB). The DVD menu allows seamless switching between them, giving each its own dedicated IFO settings.
• Pillarboxing or Letterboxing: The content is unified into a single aspect ratio before encoding. For example, 4:3 footage can be embedded within a 16:9 frame using black bars on the sides (pillarboxing), ensuring the entire stream remains 16:9 throughout the file.

Summary

A single VOB file can hold both 4:3 and 16:9 footage sequentially, and common computer media players will render the switch correctly. However, it violates standard DVD-Video authoring rules and will cause display distortion or playback failure on standalone DVD players unless properly separated into distinct title sets or padded to a uniform frame size.