Newbie Video Quality Question

[tabutcher]

Hi there,

I have an avi video file that is 140mb and I'd like to convert it to a format that is compatible with portable media players(ipod, archos etc.).

my questions are:
1. When converting I can specify the output file size and audio bit-rate; how will I be able to determine what values to set the file size and audio bit-rate? that will allow me to retain the video quality.

2. If the video bit-rate of the converted file is the same as the source does that mean: the quality is the same? the file-size is the same?

I'd like to retain quality but decrease file size.

thank-you

[guns1inger]

1. You can use a bitrate calculator to work out what values will give you the file size you are after. What values will give what quality is something that comes with experience.

2. If you re-encode a video using a different codec but exactly the same bitrate you should get the same filesize (give or take a little, as each encoder will have a little bit of drift). Will the quality be the same ? Most likely not.

You basically have three types of codec.

Uncompressed - no compression. The video is as was shot. Produces very large files.

Lossless Compression - either completely lossless - think zip file - where the video is compressed without losing any data, or visually lossless, where data is removed, but only where it has no impact on the visual quality of the video. Can reduce the size by 30 - 40%, or higher. Examples are Huffyuv, Lagarith or MSU Lossless.

Lossy Compression - The most common form of compression. Produces very small files compared to Uncompressed or Lossy Compressed. Does so by removing a lot of data while attempting to minimise the visual loss. Allows for a wider range of settings in order to get smaller files, however each reduction brings a reduction in quality. Lossy compression also compounds data loss. If you use a lossy compression on a video that has already been compressed using a lossy compression you are throwing away data that has already been stripped down. This means that the likelihood of visual artifacts appearing is far higher on a second encode, and even higher on subsequent encodes. Using the same values as the original encode will still attempt to remove data, and therefore cause loss of visual quality, even if the filesize does not change.

AVI is a container format. It says nothing about the video or audio held within. The codec used to compress the video and audio determine the size, quality, and what will play it back. Use something like mediainfo to determine what compression has been used, to see if it matches the format you need. You may find that the codecs are what you need, but the container needs to be changed for your device to play it back.

[yoda313]

Also please note that due to screen resolution and file format requirements its almost impossible to convert a video to a single file and have that play on more than 1 type of media player. For example a video for a zune won't automatically play on a ipod. You have to match the requirements and file types for each player.

Programs like super, xvid4psp, and format factory have multiple output settings and preset modes for video conversions. One of them should work for what you need. Though you may need to convert the original video more than once for you intended player. Please always use the original video to convert with instead of the converted file. That will ensure optimal conversion.

But as guns1inger said you can't expect to get exact quality on your output. It can look very good but will probably not look identical to your original video.

[tabutcher]

thank you so much

I appreciate the time you took in answering my questions.

bye for now