Wednesday, 27 April 2011

Size isn't everything - why uncompressed isn't always best.

I've run into this issue a few times recently so I thought I would write a post about it. When I am creating Watchout shows the media can be delivered in various formats. Audio can be .wav or .mp3, Images can be jpegs, .png's or Photoshop files and video can be MPEG-1 or 2, Windows media files or Quicktimes.

Now of course you want the quality of the show to be perfect, so when you are shooting and editing you work with the highest possible quality. RAW images, uncompressed quicktimes or files encoded with lossless codecs.

These are production formats and as such they are suited to editing and distribution without any loss of quality. However, they are not ideal for final playback of the material. I have had a few occasions where clients have delivered production quality content as the final media. Uncompressed Full HD quicktimes or print resolution Photoshop files.

These files are huge (Uncompressed HD can be up to 200Mb per second, that's 12 Gigabytes per minute!) and although they look fantastic they require extremely fast hardware to play them in real time. You would need a RAID array on every playback machine.

Once the editing is completed the final delivery format for video or graphics can be a compressed format, as long as the settings are correct the picture quality should still be excellent.

For HD video I normally recommend either MPEG-2 at a bit rate of 24Mbps or Quicktime using the H264 codec at around 16Mbps. The MPEG-2 files will be slightly larger (although nowhere near the size of uncompressed) but they require less intensive processing for decompression and so will playback on lower specification hardware. H264 is a great codec for distribution as it provides extremely efficient compression whilst maintaining very high image quality. (H264 is the codec used for Blu-Ray discs) However, it does require more processing power and so it should only be used when the display computers are sufficiently powerful. Some graphics cards have H264 acceleration in hardware so this might affect your choice.

It is a good idea to do a test render of a small part (choose something complex) and experiment with codec settings. Check it looks good on your computer but also test it on the playback system.

Graphics files should be RGB, not CMYK, and should not be too much larger in resolution than the display. If the display computer has to scale a huge image down to the resolution of the projector the performance will suffer.

I normally use JPG's at the exact resolution of the screen for background images and PNG's with alpha for logos and titles that will be overlaid over other content.

This also holds true for other systems than Watchout. There are many different types of media players and they all have their preferred playback formats. If somebody asks you for uncompressed video ask them why? Most media players will accept compressed formats, you just need to make sure you use the right settings.

At a recent show the client spotted a typo in a text animation which was part of an HD video. The production company work with After Effects and Final Cut Pro on a  Mac and they had to make the change and deliver a new version within four hours. They rendered a new version and then drove 100km to deliver a hard drive with an uncompressed version of the video. I have Sony Vegas Pro on my laptop so I rendered their uncompressed version to MPEG-2 and loaded it into the show. The quality was identical but the file size was 20% of the original. We had high speed internet available at the venue so they could have saved themselves the trip :-)

So remember, size isn't everything. Huge files are OK for post production but they can bring a playback computer to it's knees. They are also a pain to move around as the file sizes make ftp or other transfer systems too slow.

Find out which formats will work on the desired playback system and create the media with the best balance between quality and size.

Thanks for reading and I appreciate any questions or comments. Neil

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