Video file comparisons

I recorded a 31-second screen cast introducing myself. The original recording was made at 30 frames per second (fps) with 24-bit video and 16-bit sound sampling at 44.1khz. It was 800 x 600 pixels.

Next I saved the video and audio separately. As you see, the video file (9,779 KB) is more than 3 times as large as the audio file (2,697 KB).

Then I reduced the quality, cutting the video stream to 15 fps with 16-bit pixels and cutting the audio sampling rate to 22 kHz. That reduced the AVI file size to 3,771 KB -- around 32% of the original file.

For my next test, I saved is as a flash (SWF) file. The video specs were the same, but it used 64 kbps mp3 for the audio stream. That further reduced the file size to 1,996 KB -- around 17% of the original file.

For the next two tests, I reduced the image size from the original 800 x 600 to 640 x 480. As you see, the AVI and SWF file sizes were 7,490 and 1,474 KB, approximately 64% and 13% of the original. While the SWF file size is quite small, the video quality is compromised.

Each test to this point used the original 800 x 600 recording, but, for the next test, I started with a 640 x 480 recording. When I saved that as an SWF file, the file size was 1,727 KB, but the quality was significantly better than the reduced 800 x 600 version.

Finally, I saved the 800 x 600 version for a 176 x 144 telephone screen. That required only 184 KB, but the quality is poor.

Description Screen size File size File type

30 fps, 24-bit video, 44.1 kHz, 16-bit sound 800 x 600 11,791 KB AVI

The original recording without audio 800 x 600 9,779 KB AVI

Audio from the original recording none 2,697 KB WAV

15 fps, 16-bit video, 22 kHz 16-bit sound 800 x 600 3,771 KB AVI

15 fps, 16-bit video, 64 kb/s MP3 audio 800 x 600 1,966 KB SWF

30 fps, 24-bit video, 44.1 kHz, 16-bit sound 640 x 480 7,490 KB AVI

30 fps, 32-bit video, 64kb/s mp3 from 800 x 600 original 640 x 480 1,474 KB SWF

30 fps, 32-bit video, 64kb/s mp3 from 640 x 480 original 640 x 480 1,727 KB SWF

Cell phone size, 15 fps 176 x 144 184 KB MP4

Description	Screen size	File size	File type
30 fps, 24-bit video, 44.1 kHz, 16-bit sound	800 x 600	11,791 KB	AVI
The original recording without audio	800 x 600	9,779 KB	AVI
Audio from the original recording	none	2,697 KB	WAV
15 fps, 16-bit video, 22 kHz 16-bit sound	800 x 600	3,771 KB	AVI
15 fps, 16-bit video, 64 kb/s MP3 audio	800 x 600	1,966 KB	SWF
30 fps, 24-bit video, 44.1 kHz, 16-bit sound	640 x 480	7,490 KB	AVI
30 fps, 32-bit video, 64kb/s mp3 from 800 x 600 original	640 x 480	1,474 KB	SWF
30 fps, 32-bit video, 64kb/s mp3 from 640 x 480 original	640 x 480	1,727 KB	SWF
Cell phone size, 15 fps	176 x 144	184 KB	MP4

For me, the key lessons from these tests are:

SWF is a good format to use for Web distribution of relatively static video like a screencast, since the 64 kbps MPG audio is fine for voice narration and the video quality is acceptable.
Different settings and formats would be appropriate for other types of video, for example an action movie with music as well as voice.
As the last test shows, one should record at the same screen size as the final output, if that is possible. Resizing cuts video quality and adds to rendering time.

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