Treasured has a built-in Time Calculator that can evaluate the duration of a damaged file based on its size.
- Treasured uses a Profiles table that give a time / size relation for the most common cases.
- Time calculations are always approximate, see Bitrate section below. Repaired duration is in most cases equal or longer than what Treasured predicts.
How to use the Time Calculator tool
399 MB is 3192 Mbits (one byte, 8 bits)
3192000 divided by 4500 gives 711
IMPORTANT: This is just an estimate.
Usually the repaired duration is in the - 20% / + 100 % range.
What is the Bitrate?
In the digital media field, the bitrate is the ratio between data size and duration.
For example, a 10 seconds movie in a 500 kb file has a bitrate of 50 kb/s or 400 kbit/s.
IMPORTANT: Bitrate is usually expressed in multiples of bit/s: kbit/s and mbit/s
1 kb/s is the same as 8 kbit/s since one byte is 8 bits.
Constant, Maximum or Variable Bitrate?
By design, there is an known relation between the duration and the file size.
Since the quantity of information needed to describe a scene can vary from one to ten, between for example a black screen and a detailed, fast-moving scene, the constant bitrate is in fact the maximum bitrate. When the scene needs less information, some padding is added in the file to keep the bitrate constant.
Advanced codecs can increase or decrease the quality of audio and video to optimize the data usage: Less space is waster in padding.
Variable bitrate encoding tries to maintain the same level of quality along the movie. Scenes needing more information will need more space to be encoded. Therefore, there is not a known relation between duration and size.
Bitrate and Quality
A higher bitrate means more data, which translated into a better quality of audio and video. Less quality means less detail and more artifacts on the video.
Modern codecs like H264 are designed to work well in a vast range of bitrates: from very low for mobile devices, to very high for HD applications.
In video applications, the bitrate is a knob that you can adjust to achieve the good balance between quality and file size.
For this reason, it is hard to guess the bitrate used in a damaged file before repairing it.
Factors that determine the Bitrate
- Media type and application: some have a constant bitrate by design. End of story.
- Complexity of scene (level of detail, movement)
- Quality: Many codecs can adjust bitrate by lowering quality.
- Resolution: All other things being equal, the bitrate is proportional to the number of pixels. For example, a 1280x720 frame has 3 more pixels than a 640x480 frame, so bitrate will be 3 times as big.
- Cameras versus computers: Cameras often have a fraction of the processing power of computers and have to work in real-time. Therefore, they tend to produce higher bitrate videos, for example encoding H264 without temporal compression.
- Frame rate: When there is not enough processing power, some frames are dropped, reducing the bitrate
Bitrate can vary a lot from movie to movie, with the same recording set-up.