When you publish your project to a web format (HTML5 / Flash), iSpring will compress all pictures, audio and video files using a built-in codec. You can select the quality from 0% (maximum compression) to 100% (minimum compression).
Learn about Compression settings in the iSpring User Manual →
This article will give more details on compression for those who use a lot of media in their presentations and want to find the perfect quality/size ratio.
Image compression applies to all pictures in your presentation and vector objects that are saved as pictures during conversion (Smart Art, Charts, Text and Shapes with applied styles).
Optimize images for resolution
Use this option all the time in order to get clear images on the output presentations. If you don’t check this option, some images may be blurry: charts, graphs, and pictures that contain text. We recommend that you set the resolution to 1280 x 1024 px or higher.
The resolution you set for this option will resize every image in your presentation to this size and then include hi-res pictures in your web presentation. When you resize your presentation to fit a bigger screen, the images will still look clear. It will slightly increase the size of the output presentation but it is definitely worth it.
Note: Provided the fact that you apply image optimization, the default presentation size 720 x 540 px is okay. iSpring uses hi-res images and saves other objects in vector format, so everything looks clear on a bigger screen.
The unique Smart compression technology analyzes each image's size and content, automatically determines its type and chooses the best way of saving it for a web presentation. If the picture is small, such a bullet in a list, it will be saved in a lossless format (.png) for the best clarity. If the picture is large, such as a photo, it will be saved in a lossy format (.jpg) with compression applied.
We recommend that you apply Smart compression with a quality 80% or higher.
Properties of the audio file:
- Bitrate (320 kpbs)
- Sample rate (44,100 Hz)
- Mono/stereo channel
The output size depends on two factors:
- Mono/stereo source audio
- Compression slider
Compression chart for stereo mp3:
0% - 32 kbps; 50% - 96 kbps; 100% - 320 kbps.
Sample rate 44,100 Hz when bitrate > 80 kbps.
Audio compression applies to both:
Note: iSpring will not process MIDI because this audio file type doesn’t have any waveform data. MIDI files contain a set of instructions (similar to music sheets) for your computer’s sound card to play music.
Why do we need to compress audio files?
Audio compression is needed to save all audio files to a unified format (.mp3) and make your web presentation ready for online playback in a Web browser. Also, compression is needed to make your output presentation smaller so it will take less time to download and view it.
Thanks to the smart Audio Compression slider, your lower-bitrate audio files won’t be recompressed to a higher bitrate and cause a uselessly large output size.
How does the audio slider work?
The audio compression slider lets you choose the average quality of the audio in percent. It doesn’t give you an option to have a constant bitrate (kbps value) because audio files may have a different bitrate (from 32 kbps to 320 kbps), or uncompressed. Each audio will be compressed individually according to the percent value.
If you set a 100% value, no compression will be applied to the source audio. 320 kbps audio will remain 320 kbps and 32 kbps will remain 32 kbps.
If you downscale, the smart algorithm will compress high-bitrate audio more and low-bitrate audio less to some threshold level. Threshold here means that if you move the slider all the way to 0%, you will get very low-bitrate audio output, but not 0 kbps.
We recommend that you set the quality to 70% or higher.
Video compression applies to both:
Video files in your original PowerPoint presentation file (.mp4, .avi, .wmv, .mov, .mpeg, etc.).
iSpring-recorded video files (uncompressed .mkv format).
Why do we need to compress video files?
Like audio compression, video compression is needed to save all video files to a unified format (.mp4) to make your web presentation ready for online playback in a Web browser. Video compression is even more essential to to make your output presentation smaller, so it will download faster and not take much time to wait before viewing.
Thanks to the smart Video Compression slider, your lower-bitrate video files won’t be recompressed to a higher bitrate and cause a larger output size with the same quality.
How does the video slider work?
The video compression slider lets you choose the average quality of the video in percent. It doesn’t give you an option to have a constant bitrate (kbps value) because video files may have a different bitrate. Each video will be compressed individually according to the Video Compression setting.
The video files have several properties:
If you set a 100% value, no compression will be applied to the source video and it will remain the same.
If you downscale, the smart/adaptive algorithm will compress high-bitrate video more and low-bitrate video less to some degree.
We recommend that you set the quality to 60% or higher.
The output size depends on these factors:
- Video dynamics (movements)
- Video controls option (on by default)
- Optimize images for resolution
- Scale presentation
- Player settings (narration video max 1366 x 1024 px)
Audio from video is processed using audio compression settings.