Encoding Settings

Encoding settings determine how the Ooyala Transcoding Service encodes streams created during the transcoding process.

Content Width and Height

The width and height specify the size of the video (in pixels). The Ooyala Transcoding Service maintains the aspect ratio of the source video using the width and scaling the height accordingly.

If a device (such as a phone or tablet) cannot support the width of a video, it will not be play. Additionally, phones and tablets are often connected to the Internet through lower bandwidth connections. As a result, you will want to make sure your lower bit rate encodings have a smaller width. For example, if you created an encoding with a 1280 width and a 300kbps bit rate, it would not be able to play on an iPhone with a maximum width of 640.

Larger screens look better in higher resolution and tend to have better bandwidth. Reserve your higher bit rate encodings for larger widths. For example, you might specify a width of 1280 for your 1500, 2200, and 3600kbps bit rate encodes.

The following table shows the width and height of common devices.

Device Width Height
iPhone 3GS 640 or lower 480 or lower
iPhone 4/4S/5 960 or lower 640 or lower
iPad 1/2 1024 or lower 768 or lower
iPad 3/4 2048 or lower 1536 or lower
Apple TV 640 or higher 320 or higher
Android varies (960 or less recommended) varies (640 or less recommended)
Desktop/Notebook varies (1280 recommended) varies (720 recommended)
TV varies (1920 or less recommended)

Note: If you specify a width of 0 in your encoding profile, the content uses the source file’s width.

Flash playback and video encoding works best with even numbers. Widths with multiples of 16 are best, but 8, 4, and 2 are also acceptable. Common widths are 400, 480, 520, 640, 800, 1280.

Containers, Video Codecs, and Audio Codecs

Each encoding is a container format (e.g. MP4) which comprises a video and audio codec.

When specifying a processing profile, the container formats and audio formats must be specified.

H.264 specifies a set of capabilities and different profiles that group subsets of the available capabilities. Ooyala supports the following profiles:

  • Baseline
  • High

Although the High profile will give you better quality, it is not supported by all devices (including iPhones, as they require the Baseline profile).

Note: For the same video, the Baseline profile can require up to a 20% higher bit rate to provide the same quality as the High profile.

Resolution

If a device, such as a phone or tablet, does not support an encode’s resolution, the video will not play. This is usually not an issue for desktops and laptops, but can be an issue for phones and tablets.

Video Bitrate

The video bit rate specifies the amount of bits in one second of video. In general, the higher the bit rate, the higher the video quality.

When a bit rate is specified for an encoding, the actual bit rate is not consistent during playback. Variable bit rate (VBR) stores more data for the portions of videos that have a high level of change between frames (e.g., action scenes) and less data for portions that have little change. As a result, the bit rate will vary during playback, but the average will be the bit rate you specify.

Ooyala uses a two-pass encoding method o optimize performance and video quality. The first pass analyzes the content to determine the bitrate for each part of the video. The second pass encodes the video based on the analysis.

Note: To prevent excessive switching between encodings, we recommend making sure that each encoding of the adaptive bitrate (ABR) profile is at least 300Kbps (kilobits per second) apart (e.g., 300, 600, 900, and 1200 instead of 300, 450, 600, and 750).

Audio Bitrate

The audio bit rate is the number of bits in one second of audio. The higher the audio bit rate, the higher the quality, and viewers’ bandwidth requirements. You can select any audio bit rate of up to 156kb/s. For example:

  • 32Kbps (kilobits per second)—AM Radio Quality
  • 64Kbps—Voice Quality
  • 96Kbps—FM Radio Quality
  • 128Kbps—Standard Quality (recommended)
Note: If possible, we recommend that all encodings use the same audio bit rate. Otherwise, some viewers might notice the audio level change as the player switches encodings.

Audio Sample Rate

The audio sampling rate specifies the number of samples taken per second. Ooyala supports all audio sampling rates up to 48,000, but we recommend the following rates:
  • 32,000 (miniDV)
  • 44,100—(CD)
  • 48,000 (professional digital video equipment)
Note: If possible, we recommend that all encodings use the same audio sample rate. Otherwise, some viewers might notice the audio level change as the player switches encodings.

Smooth Playback

The following are just a few of the variables that can affect a viewer's playback experience:

  • The CPU and GPU abilities of the device; other programs running in the background

  • The viewer's device and screen size

  • The connection speed or bandwidth cap

  • Latency caused by the wireless router, such as the distance from the router and local congestion

  • Latency caused by network traffic between the device and server hosting the video

  • Viewer's browser brand, version, and available plugins (e.g., Flash, Silverlight, and so on)

For smooth playback, viewer bandwidth should be around double the video playback bitrate (audio plus video bitrates).

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