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Preloading

From: HTML5: Video and Audio in Depth

Video: Preloading

One option we have with HTML5 video is preloading. Preloading means the browser will begin loading the video data as soon as the page is loaded instead of waiting until the user clicks Play. Without preloading, the user might have to wait a little bit while the video buffers enough data so it doesn't have to buffer again later during playback. A downside of preloading is that the video data is loaded every time the page is viewed, even if the user never watches the video. This can cause waste of bandwidth and unnecessary cost for you and your users, especially those on mobile devices where data transfer can be expensive.

Preloading

One option we have with HTML5 video is preloading. Preloading means the browser will begin loading the video data as soon as the page is loaded instead of waiting until the user clicks Play. Without preloading, the user might have to wait a little bit while the video buffers enough data so it doesn't have to buffer again later during playback. A downside of preloading is that the video data is loaded every time the page is viewed, even if the user never watches the video. This can cause waste of bandwidth and unnecessary cost for you and your users, especially those on mobile devices where data transfer can be expensive.

So there are good and bad times to use it and we will go over that in a second but first let's see how it is that we do use it. To add preloading first let's go back to our code. We're now in the 2-03 folder of the exercise files. I need to add the preload attribute and a preload attribute is an enumerated attribute which means it can take one of a limited number of values. In this case preload has three possible values: none, auto, and metadata.

So, if we set the value to none, Save that and go to our web browser, and re-load it, we can see that it doesn't actually load any of the video. It doesn't load the first frame, the size of video, or any information. That's what preload="none" does. It tells the browser to load nothing. Okay let's go back to our code and the next option is auto. So save that and go to our web browser and reload it. It's now loading that first frame, size of video, and it's continuing to load the entire video.

So what we're telling the browser with the auto setting is that we're not concerned about bandwidth with this particular video, and so if the browser feels like it's the best choice for the user, it can load the entire video. So basically we can either say don't preload or leave it up to the browser to decide. In the case of Apple IOS devices, they've made the decision that it's never good to preload for their users because their users are on mobile connections where bandwidth could be expensive. So even with the auto setting, the video won't preload on an iPhone. It definitely makes sense for them.

All the desktop browsers I've tested however will preload the video if you use the auto setting. Okay, now the third option is metadata and save that and reload and see it looks the same. It's loading the first frame and the metadata. It's basically telling the browser to load the metadata of the video which includes information like the video frame size, duration and the first frame but not the rest of the video. This can help reduce the initial buffering time a little but not nearly as much as fully preloading the video.

Preloading the metadata can be helpful in cases where you want the browser to know how big the video is ahead of time so that the browser can size the space for the video correctly or if you have a poster frame burned into the first frame of the video. However as of now, the only browser that appears to support the metadata setting correctly is Firefox version 4. Chrome 10, Safari 5, and older versions of Firefox just preload the entire video as if you'd use the auto setting. If you are trying to decide which setting to use a good rule of thumb is to only preload the video if video is the main focus of the page or if you're pretty sure the user will watch the video and you want it to be responsive.

Otherwise set preloading to none, especially on pages that have many videos on them. So in the case of our page here, the podcast is the main focus of the page, so we will set preload to auto. The audio only version however is less likely to be played so we will set preload to none and save that. I would be suggesting using the metadata setting instead of the none setting because it's relatively a low amount of bandwidth and can't help the browser get a jump on processing video or audio.

But since most browsers are treating metadata just like auto and preloading the whole video or audio, none is the better choice.

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This video is part of

Image for HTML5: Video and Audio in Depth
HTML5: Video and Audio in Depth

37 video lessons · 14608 viewers

Steve Heffernan
Author

 
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  1. 1m 24s
    1. Welcome
      42s
    2. Using the exercise files
      42s
  2. 15m 18s
    1. Understanding HTML5 video and audio
      4m 46s
    2. The state of HTML5 video and audio
      4m 29s
    3. Understanding the format war
      3m 53s
    4. Configuring your server to deliver HTML5 media formats
      2m 10s
  3. 32m 36s
    1. Using the video and audio tags
      5m 34s
    2. Using multiple sources for browser compatibility
      5m 53s
    3. Preloading
      4m 16s
    4. Autoplaying
      2m 2s
    5. Looping
      5m 11s
    6. Setting a poster frame
      3m 43s
    7. Setting the video width and height
      3m 40s
    8. Displaying subtitles and captions
      2m 17s
  4. 12m 40s
    1. Falling back to Flash
      4m 4s
    2. Falling back to download links
      6m 21s
    3. Using an embed code builder
      2m 15s
  5. 22m 17s
    1. Understanding HTML5 video formats
      5m 10s
    2. Understanding HTML5 audio formats
      2m 57s
    3. Encoding MP4/H.264 video with HandBrake
      3m 13s
    4. Encoding Ogg, Theora, and WebM with Firefogg
      3m 18s
    5. Encoding audio formats with VLC
      5m 54s
    6. Automating video and audio encoding
      1m 45s
  6. 34m 59s
    1. Setting up the JavaScript
      4m 39s
    2. Creating Play and Pause buttons
      7m 52s
    3. Creating a Play Progress bar
      5m 49s
    4. Creating a Load Progress bar
      9m 29s
    5. Creating a Current Time and Duration display
      7m 10s
  7. 4m 37s
    1. Overview of known issues
      35s
    2. Autobuffer or preload?
      56s
    3. Load progress in Firefox 3.6
      41s
    4. Android 2.0 issues
      1m 5s
    5. iOS 3 issues
      1m 20s
  8. 2m 8s
    1. Flight of the Navigator
      50s
    2. ZEN Audio Player by simurai
      34s
    3. The Wilderness Downtown by Google and Arcade Fire
      44s
  9. 1m 40s
    1. Further exploration
      1m 40s

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