Video Encoding Parameter Calculator

I wrote a free utility iPhone application to help video encoding professionals and consumers calculate bitrates and file sizes as well as aspect ratios and dimensions. It is called the VidCalc.

You can get it at the app store for free. Please be sure to give me some feedback. Visit my website for the app at http://www.valenzj.com/ for more info.

I would like to know if it is usefull at all and what features you would like me to add to the application.

AviSynth

AviSynth is a frame server –it feeds uncompressed frames to other applications directly- that can be scripted to automate image processing and editing of videos.

It is not a video editing or special effects workstation. Its strengths lie on allowing the video professional to pre-process videos to resize, crop or remove noise and to conform video sources with simple cuts. Basically you create a script that indicates AviSynth which filters to apply in what order. If you are not comfortable with writing scripts in text form, you could use VirtualDubMod or MeGUI graphic user interfaces to create them.

AviSynth comes very handy when preparing videos for compression in an automated and streamlined fashion. In particular, you can perform noise reduction, resizing and color conversions to ensure that the compressed video looks as best as possible.
It is an open source project that has many followers. Check it out:

http://avisynth.org/mediawiki/Main_Page

Fonts

Fonts of different types and sizes look different across video displays and resolutions. Therefore, choosing the right font size is critical to ensure readability on the final encoded video.

Some broadcasters recommend that as a rule of thumb font sizes to be displayed on an HD 1920 x 1080 video should be about 80% of the sizes used in SD. For example, you have been using a font that is 23 scan lines high on SD NTSC. First we consider the ratio of the HD / SD heights: 1080 / 486 = 2.22 and 80% of 2.22 is 1.776. Use 1.776 as the font scaling factor. That means that our new font size is 23 x 1.776 = 41 scan lines high (with rounding.)

Always check how your titles look in the target player and display to be sure that the text is readable and that aesthetics translate.

Audio Quality

Some studies have pointed out that the human brain puts together both audio and images as a single message and therefore audio has a tremendous impact on viewer experience. Some research has even pointed out that viewers are less likely to completely view a video clip if the audio quality is poor.

Below is a list of audio encoding artifacts to check for as well as some tips.

• Lip-sync. Most people find "out-of-sync" audio as unacceptable.
• Audio drop outs and pre- echo are perceived as “very annoying” artifacts by most people. They tend to be more prevalent in material that is percussive like a gunshot or a drum hit. Increase the bit rate as much as possible to compensate.
• Narrow audio program bandwidth. If high audio frequencies have been removed, the audio will sound “nasal” or “muddy”. If Low audio frequencies have been removed, the audio will sound “thin” and “harsh”. Make sure the resulting audio covers as much frequency spectrum as the original. Keep the audio sampling rate the same as the source or above 44.1 KHz for best results.
• “Garbled” audio due to over compression tends to have sort of an underwater sound. These artifacts will be more noticeable in material that has random characteristics like rain, applause or city traffic. Give enough bits to the audio stream. Try to keep audio bitrates above 96 kbs for best results.
• Summing some stereo material to mono will cause phasing artifacts and audio dropouts. Experiment by taking only the left or only the right channel if you hear this artifact. You might get better results.
• Audio re-sampling or clock errors often have a metallic / ringing sound and can produce loud ticks. If you are encoding video from tape or other hardware playback device, make sure the audio is properly clocked and sync-locked. When using AES/EBU or SPDIF audio, clock your input device to the source’s digital signal as a rule of thumb.
• Make sure the audio is noise (hiss) free. Be careful of not going overboard if you have to pre-process the audio with noise suppression as you might induce more serious artifacts. Also, make sure that your audio has the required bit resolution. Today, 16 bit audio is common place. Avoid a lower value.

De-interlacing algorithms

De-interlacing algorithms can be sub divided into two broad categories:

1. Spatial Based
2. Motion Based

Some popular spatial based algorithms are:

• Simply weaving the odd field and doubling each line. (Produces aliasing)
• Averaging or blending both fields. (Produces ghosting)
• Edge dependent interpolation techniques between adjacent lines in odd-even fields. (Few artifacts if edge direction is inaccurate)

Some motion based algorithms are:

• Selective blending (or motion adaptive blending) basically only blend areas where there is motion and weaving where there is none. (Few artifacts if motion calculation is correct)
• Motion and edge adaptive algorithms combine edge interpolation techniques and motion adaptive blending. (Fewer artifacts at computational expense)
• Motion compensated algorithms can use the information to find the matching blocks in the neighboring fields. (Fewer artifacts at computational expense)

Be sure to check what algorithms your encoding software implements, it might have a great impact in your final video quality.