H.264 (mp4/m4v) Tips – Blubrry

H.264 is a standard for video encoding for online distribution. It’s also the most used for video podcasting using the .mp4 or .m4v file extension. You can use H.264 to encode other types of video files, but for podcast use, it’s best to stick with .mp4 or .m4v.

MP4 is very close to Apple’s Quicktime format with some added features.

M4V is Apple’s slightly different version of MP4 for iTunes
MOV is Quicktime format

We recommend you use MP4 as it is the most widely compatible file format.

For more information on the different video formats, see: Video Formats

Common video sizes (also known as video resolution) in use for podcasting and online streaming sites like YouTube are:

640×480 – Standard Definition 4×3 aspect ratio (YouTube minimum recommended)
960×640 – Standard Definition 4×3
1024×768 – Standard Definition 4×3
640×360 – Standard Definition 16×9 Widescreen
1280×720 – High Definition 16×9 Widescreen (otherwise known as 720p, YouTube minimum recommended)
1920×1080 – High Definition 16×9 Widescreen – ** not used currently as they produce REALLY large files

Any of these sizes will work nicely for your podcast video, Remember to take great care picking a video size that provides a reasonable file size. Please see below for e more details on video file sizes.

High Definition (HD) refers to the minimum height resolution to the screen. Any screen height resolution of 1080 pixels (1080p) or greater meets the HD requirement. A screen size of 1920×1080 is considered HD.

Streaming

It is important that you have your file setup for streaming. This way it will start playing after buffering a short time inside of the Flash or html5 players on your page.

When you encode your video file, it needs to be setup for streaming for it to “progressively download” and play while downloading. Settings to look for in your video encoding software are things such as “hinted streaming”, “adaptive steaming” or just “streaming” in the output settings. There is some meta data in the file that are called Atom tags. These tags need to be in the front of the file to make the file stream while the file is downloading.

Here are a few programs that will fix the meta tags in your file if your encoding software doesn’t put the tags at the front of the file:

Video media file hosting tips

Don’t use free services such as Archive.org for newly released episodes. Free services do not guarantee delivery of large media like a paid Content Delivery Network (CDN) would and they will throttle/kill excessive downloads rather than host your media for free.
Do not host your media on the same server as your website. The large media file downloads can cause your website to come to a crawl the first few hours your episodes are released.
Make sure your Web server reports the correct content type for your media file. Mp4 should report as Content-Type “video/mp4.” This is typically not a concern, but can explain why the media file does not play in the computer’s default media player when downloaded.
Always make sure your files have the appropriate file extensions (e.g. file.mp4), iTunes and many other applications determine the file content type based on the file extension.
Only use the 26 English letters, 0-9 numbers and underscore/dash characters for file names and folders. Some applications will not capture the special characters, such as dollar signs or commas, correctly from the file name, which could make the saved file unplayable on the target device.
Never use spaces in your files and folders (same reason as above).

Estimating video file sizes

The following is a rough estimate of the mp4 file size per minute based on different aspect ratios using 25 frames per second in H.264.

640×480 (4×3 aspect ratio) Letterbox: 65MB/minute
640×360 (16×9 aspect ratio) Widescreen: 50MB/minute
1280×720 (16×9 aspect ratio, otherwise known as 720p) Windscreen: 190MB/minute
1920×1080 (16×9 aspect ratio, otherwise known as 1080p) Widescreen: 420MB/minute

Keeping episodes within a manageable size

We recommend keeping video files under 1GB in size for the reason’s listed.

Large files fill up devices faster. A 1.5GB download on an iPhone or iPad to a viewer mean the difference of keeping their family photos or their favorite game vs. watch your podcast.
Bandwidth consumption may harm your viewers. In a perfect world your viewers will use WiFi that is not throttled. Unfortunately, not only do cell phone plans have 2-4GB/month bandwidth limits, many households have bandwidth limits through their hard wired Internet providers as well.
Playback performance can be impacted if the video files are not hosted on a Content Delivery Network designed to allow for streaming video. This is the case if you have to wait seconds when skipping to a further position into the video during playback in a web browser.

It is not uncommon for the length of your video to determine the aspect ratio you use to meet file size requirements. Take the following scenarios into consideration.

A 3 minute 1920×1080 video will have a file size of approximately 1,260MB, or 1.3GB
A 6 minute 1280×720 video will have a file size of approximately 1,140MB, or 1.1GB
A 24 minute 640×360 video will have a file size of approximately 1,200MB, or 1.2GB

Note: Bitrates vary. The above assumes typical bit rates for the various video resolutions.

Frame Rate

Frame rates include 24, 25, 30, 48, 50, 60. A general rule, the video should be encoded in the same frame rate it was recorded. 24, 25 and 30 are known as Standard Frame Rates. 48, 50 and 60 are known as High Frame Rates.

Video Bitrates

Video bitrates effect both the quality of the recording as well as the size. Bitrates can range from 1Mbps to as high as 68Mbps. Typically a 1-2.5Mbps rate is used for podcasting as a compromise to quality and file size.