6 ответов в этой теме

[maksimus]

Собственно вопрос в теме.
Ясно что алгоритм сжатия другой, но какой?
Если можно ссылку или обьясните.

[Ancle Fedor]

Максим, извини, но IMHO тебе никто не ответит.
Очень всё "закрыто".
Пока.
Олег.

[MetroidZ]

На английском можно найти.
Reduce MPEG size
This will reduce bitrate of the mpeg file and its size using DCT-Domain Transcoder (DCT = Discrete Cosine Transformation). DCT is not a full file transcoding, it reuses the existing Motion vectors and therefore the recompression is extremely fast. The reasonable resizing is up to 70%. The DCT transcoder will try to resize as much as possible to the desired new size, however this may not be actually realistic for sizes below 50% of original size. or for short movies. It works on elementary streams only.


DCT-Transcoder should be used only in extreme cases when you need quickly reduce file size/bitrate. A full mpeg transcoding will produce better result.

DCT. Discrete cosine transform. Дискретное косинусное преобразование. Математический алгоритм, используемый для генерации частотного представления блока видеопикселов. DCT — это обратимое дискретное ортогональное преобразование между пространственной и временной областями. Есть прямое дискретное косинусное преобразование (forward discrete cosine transform, FDCT) и обратное дискретное косинусное преобразование (inverse discrete cosine transform, IDCT).


DCT-based video downscaling transcoder using split and merge technique
Abstract
For a conventional downscaling video transcoder, a video server has firstly to decompress the video, perform downscaling operations in the pixel domain, and then recompress it. This is computationally intensive. However, it is difficult to perform video downscaling in the discrete cosine transform (DCT)-domain since the prediction errors of each frame are computed from its immediate past higher resolution frames. Recently, a fast algorithm for DCT domain image downsampling has been proposed to obtain the downsampled version of DCT coefficients with low computational complexity. However, there is a mismatch between the downsampled version of DCT coefficients and the resampled motion vectors. In other words, significant quality degradation is introduced when the derivation of the original motion vectors and the resampled motion vector is large. In this paper, we propose a new architecture to obtain resampled DCT coefficients in the DCT domain by using the split and merge technique. Using our proposed video transcoder architecture, a macroblock is splitted into two regions: dominant region and the boundary region. The dominant region of the macroblock can be transcoded in the DCT domain with low computational complexity and re-encoding error can be avoided. By transcoding the boundary region adaptively, low computational complexity can also be achieved. More importantly, the re-encoding error introduced in the boundary region can be controlled more dynamically. Experimental results show that our proposed video downscaling transcoder can lead to significant computational savings as well as videos with high quality as compared with the conventional approach. The proposed video transcoder is useful for video servers that provide quality service in real-time for heterogeneous clients.

DCT
http://compression.graphicon.ru/download/v..._streaming.html

http://compression.graphicon.ru/download/a...scaling_pdf.rar
318 кбайт

google

Сообщение отредактировано MetroidZ: 23 фев 2006 - 14:54

[maksimus]

Спасибо за инфу.
Понял что ничего не понял :-)
все так заумно.

[Ancle Fedor]

Игорь, извини, в английском не очень силен.
Можно чуть-чуть по русски (в своих словах) про разницу между кодировщиками DVD Lab и DVD Shrink. Или я не понял поднятый вопрос?

[maksimus]

Я не имел в виду разницы между ними. Мне сдается что у них алгоритм один. Вот хочется понять, а в инглише ( тем более техническом) - бум-бум ( точнее НЕ БУМ)

[Ancle Fedor]

Ну значит я немного непонял.