WebM VOD Baseline format

The WebM Video on Demand (VOD) baseline format for adaptive streaming are Non-Chunked and Non-muxed files.

Figure for Separate Non-chunked files.

Information on Decision Process

Adaptive streaming can be done with many different file formats and features. Different formats will pose tradeoffs in areas such as complexity and storage. Below are four choices for the physical layout of WebM VOD files for adaptive streaming.

1. Muxed and Non-Chunked

2. Muxed and Chunked

3. Non-Muxed and Non-Chunked

4. Non-Muxed and Chunked

Discussion of the Four Formats

1. Muxed and Non-Chunked

• • Pros

    • There is already a lot of content as this is the format most websites use today for progressive download.

    • Tools already have support.

    • File management is easy. Number of files equals number of audio streams * number of video streams [ * number of text streams].

  • Cons

    • Storage does not scale well. Size of data equals num video(A0 size + ... + An size) + num audio(V0 size + ... + Vn size). (Some combinations could be optimized out)

    • Switching may be more complex depending on frame alignment and stream interleaving.

2. Muxed and Chunked

• • Pros

    • Format of the de-facto leader in adaptive streaming.

  • Cons

    • Storage does not scale well. Size of data equals num video(A0 size + ... + An size) + num audio(V0 size + ... + Vn size).

    • Switching may be more complex depending on frame alignment and stream interleaving.

    • File management is complex. Number of files equals number of chunks * number of audio streams * number of video streams [* number of text streams].

    • Extraneous downloaded bytes may be bigger. This depends on if there is an requirement that each chunk be a fully formed WebM file as the setup data for Vorbis can be fairly big.

3.  Non-Muxed and Non-Chunked

• • Pros

    • Storage scales well. Size of data equals (A0 size + ... + An size) + (V0 size + ... + Vn size).

    • Switching may be easier than the other formats because you do not need to worry about alignment of other interleaved streams.

    • File management is easy. Number of files equals number of audio streams + number of video streams [+ number of text streams].

    • Cache invalidation of only one stream when one stream needs to be added/removed/changed.

  • Cons

    • Current tools support is small.

    • Currently relatively unused format.

4. Non-Muxed and Chunked

• Pros

  • Storage scales well. Size of data equals (A0 size + ... + An size) + (V0 size + ... + Vn size).

  • Switching may be easier than the other formats because you do not need to worry about alignment of other interleaved streams.

• Cons

  • File management is complex. Number of files equals number of chunks * (number of audio streams + number of video streams [+ number of text streams]).

  • Extraneous downloaded bytes may be bigger. This depends on if there is an requirement that each chunk be a fully formed WebM file as the setup data for Vorbis can be fairly big.

  • Current tools support is nonexistent.

  • Currently unused format.

WebM VOD Baseline Format Choice

The heaviest weighted decision point is storage, which downgrades muxed formats 1 and 2. Format 3 is better than format 4 because of file management and tool support. Format 3 (Non-chunked, Non-muxed) is the choice for the baseline format of WebM VOD files for adaptive streaming. The cons for format 3 should be overcome as adaptive streaming is fairly new and there is not a lot of content currently.