There are many factors that impact the overall results of transcoded media. It is not realistic to provide a one-size-fits-all recommendation, so this step will list some of the more important considerations and how they affect the output.
- H.264 and AAC are the preferred video and audio codecs to be used.
- Do not use multiple video or audio streams. Occasionally we see source media that may have more than one audio or video stream. This is often the case with media copied directly from a DVD. While we make a best guess as to which stream to use, there is no way for us to know what stream was preferred.
- Avoid stream delays. For example, some video editing tools will inject a start time for the audio stream such that the audio starts playing at some time after the video. We have found that some tools introduce audio sync issues during this process.
- The frame size should be at least as large as the largest anticipated rendition. However, do not scale media to a frame size larger than the original.
- H.264 requires that frame sizes are multiples of 4 and is optimized for multiples of 16. We will scale transcodes to meet this requirement, but for best results source media should already be encoded in multiples of 16. Multiples of 8 or 4 will also work though with a slight performance decrease.
- Avoid interlacing. Most web and mobile video players do not handle interlaced content well.
- Avoid anamorphic video. Anamorphic video, or video with a non-square Pixel Aspect Ratio, does not play correctly in some mobile and Web players
- If creating a screen cast with a tool such as Camtasia, try to use the highest quality settings. For example, in Camtasia export as MP4 and "Best Quality". Avoiding highly compressed screen casts, which is common with these tools, will help us reduce quality loss in subsequent transcodes. Also avoid exporting video with a variable frame-rate if it is an option.
- For maximum compatibility, use stereo or mono audio and avoid 5.1.
- Sample rates above 44.1 kHz do not work on all players so will be re-sampled. Avoid this by sticking to 44.1 kHz or less.
- Normalize the audio tracks to standard levels such that you avoid "audio clipping" while also avoiding a low volume.
- Make sure that audio levels are consistent across media that might be viewed together.