At iPlayerHD, as the name would imply, much of the video content uploaded to our platform has, as it’s source, high definition resolutions. Not surprisingly, much of the video uploaded is also standard definition. There are still many folks shooting with older cameras and there is an abundance of legacy video shot in non-HD resolutions. iPlayerHD, like most video hosting platforms, works hard to deliver the best quality viewing experience. To deliver the best quality requires some assistance from those who create and upload video to our site. This is truly a case of “beauty in, beauty out”.
Once the video edit process has been completed, a video to be uploaded to a video hosting site is prepared and rendered much differently than a video that will be viewed on a DVD. There are several items to consider including codec, container, bitrate, framerate and resolution. Many sites, including iPlayerHD, will convert, or encode videos to a specification that is consistent with their product offering. For example, iPlayerHD, with it’s device and bandwidth detection feature, will create multiple versions of a video, the highest of which will have a 1280 x 720 resolution with a bitrate at over 2000 kbps, with lower resolutions and bitrates created to optimally match the device viewing the video.
The best source video will have an H264 codec – think of a codec as the recipe that you use to make a great salsa, an MOV or MP4 container – think of a container as the jar you put the salsa in. It will have a resolution of 1920 x 1080 or 1280 x 720 if it is high definition and the native rate if it is not HD, 720 x 480, for example. The framerate can be the native framerate – this will converted to an acceptable web deliverable framerate, and if it is interlaced, it may be deinterlaced before you upload although most platforms, including iPlayerHD, will deinterlace any video that arrives in an interlaced format.
Of extreme importance is the video’s bitrate. Optimizing a video to over 2000 kbps, as iPlayerHD does, and expecting a high-quality result requires the source video to have a much higher bitrate. iPlayerHD recommends a bit rate at about 2.5 times the bitrate of the rendered video. That’s about 5000 kbps.
The bitrate of a video is generally measured in kbps while the file size is measured MB or GB. There is a simple rule of thumb that may be used when calculating the file size of a video when encoded at a certain bitrate. At a 1000 kbps video bitrate and a standard 96 kbps audio rate, a one minute video will have an approximate 8 MB file size. You may use those numbers to calculate any file size. For example, a 15 minute video, at 5000 kbps would have a 600 MB file size.
Number of minutes x 8 MB file size per minute of video x (video bitrate/1000 kbps)
or, in this case
15 minutes x 8 MB file size per minute of video at 1000 kbps x (5000 kbps/1000 kbps).
HTTP has a maximum file upload size limit of 2 GB. There are other methods of uploading that do not use HTTP so that file sizes may be larger than 2GB. iPlayerHD has purposely limited it’s file size to that of the HTTP maximum. Video lengths are not restricted but since the file size is, the bitrate of a very long video must be reduced to keep the file size at 2GB or less.
When your video is encoded, all platforms place specific kinds of information at the beginning of the video so that the player, in this case the Flash player, knows what to do with the video. Included in that information are the items discussed above. Just as important is an instruction that tells the player to start the video playing immediately and not wait until the file is downloaded. Without this vital instruction, a video will not begin to play until the entire file is downloaded, or cached to the machine viewing the video. All platforms encode using this spec so you need not be concerned about this. However, for those who prefer to encode their own videos – iPlayerHD allows its customers to encode and upload their own videos, averting our encoders – it is imperative that the video is encoded as a fast start file.
To summarize, render your videos for uploading to video hosting platforms as H264 MP4 or MOV files at a high, native resolution, at about 2.5 times the bitrate of the highest bitrate created, and using all of the native framerates and other parameters specific to the source video. A quality encoder will do all of the heavy lifting and produce a result that will make your videos look stunning.