BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Decoding video          BorlandTalk.com Forum Index -> Delphi Multimedia View previous topic :: View next topic   Author Message Jon Lennart Aasenden Guest Posted: Wed May 12, 2004 7:00 am    Post subject: Decoding video Hi guys. I realize that decoding video today, is a two step process: 1. reading the fileformat (and buffering data) 2. sending the data to a codec for decompression 3. displaying the data But just out of curiosity, would it be possible to decode, and display, a video under native pascal without calling DirectX or some external dll? I have heard of native delphi mp3 decoders, that does all the work in pure pascal (and that works), but in theory the same could be done for video right? Have there ever been a codec written in delphi? Jon Lennart Aasenden, Norway Back to top Avatar Zondertau Guest Posted: Wed May 12, 2004 7:17 am    Post subject: Re: Decoding video Quote: I realize that decoding video today, is a two step process: 1. reading the fileformat (and buffering data) 2. sending the data to a codec for decompression 3. displaying the data Two steps? Quote: But just out of curiosity, would it be possible to decode, and display, a video under native pascal without calling DirectX or some external dll? Yes, this would definately be possible, but it would have many disadvantages. First the speed will be a problem if you're not using DirectX or something similar. Second you would have to implement a whole lot of codecs and add new ones each time another codec gains popularity. Normally codecs are installed seperately and they can then be used by any program that wants to play video. Many video file formats (like avi) can handle any of these codecs, so to be able to read all video files stored in that forma you'll have to implement all codecs ever made. Quote: I have heard of native delphi mp3 decoders, that does all the work in pure pascal (and that works), but in theory the same could be done for video right? If you would implement all codecs it would be possible, but this is much more work than mp3, which only uses a single codec. Back to top Jon Lennart Aasenden Guest Posted: Wed May 12, 2004 1:43 pm    Post subject: Re: Decoding video Well, i would not want to create all the codecs, but perhaps set a standard to mpg file format, compressed with the xine codec or somthing. Most video formats seem to use RLE compression? Where only the difference from the last frame is stored as a new frame, right? This is probably why it takes a second when fast forwarding before the frame is displayed, because mediaplayer has to backtrack to get the last keyframe + previous frames to build the correct "current" frame. Any hints to where i can find the C++ source for the xine or divx codecs? Is divX open (it was stolen from Microsoft was it not?) or is it a closed API? Jon Lennart Aasenden "Avatar Zondertau" <avatarzondertau (AT) hotmail (DOT) com> wrote Quote: I realize that decoding video today, is a two step process: 1. reading the fileformat (and buffering data) 2. sending the data to a codec for decompression 3. displaying the data Two steps? But just out of curiosity, would it be possible to decode, and display, a video under native pascal without calling DirectX or some external dll? Yes, this would definately be possible, but it would have many disadvantages. First the speed will be a problem if you're not using DirectX or something similar. Second you would have to implement a whole lot of codecs and add new ones each time another codec gains popularity. Normally codecs are installed seperately and they can then be used by any program that wants to play video. Many video file formats (like avi) can handle any of these codecs, so to be able to read all video files stored in that forma you'll have to implement all codecs ever made. I have heard of native delphi mp3 decoders, that does all the work in pure pascal (and that works), but in theory the same could be done for video right? If you would implement all codecs it would be possible, but this is much more work than mp3, which only uses a single codec. Back to top Avatar Zondertau Guest Posted: Wed May 12, 2004 2:59 pm    Post subject: Re: Decoding video Quote: Well, i would not want to create all the codecs, but perhaps set a standard to mpg file format, compressed with the xine codec or somthing. You could do this, but of course this would mean you'll not be able to play all videos. Quote: Most video formats seem to use RLE compression? Where only the difference from the last frame is stored as a new frame, right? I don't think so. RLE is a lossless form of compression and therefore results huge video files. I don't think it's useage is very common except for, perhaps, small and very short movies. Quote: This is probably why it takes a second when fast forwarding before the frame is displayed, because mediaplayer has to backtrack to get the last keyframe + previous frames to build the correct "current" frame. About every video compression algorithm uses the concept of keyframes. They store the keyframes entirely (probably in some JPEG-like format) and store only some data for other frames to use for interpolation. Quote: Any hints to where i can find the C++ source for the xine or divx codecs? Is divX open (it was stolen from Microsoft was it not?) or is it a closed API? DivX is not open source and AFAIK has nothing to do with Microsoft. XviD (guess where the name came from ...) is a good opensource MPEG4 codec though, which, i think, also supports DivX. Information on the project and sourcecode downloads can be found at: http://www.xvid.org/ Back to top Patrick Guest Posted: Wed May 12, 2004 11:20 pm    Post subject: Re: Decoding video Quote: DivX is not open source and AFAIK has nothing to do with Microsoft. DivX and XVID, used to be the same thing (named DivX; open source). If I understood it right, the DivX-licence has either been sold, or they changed the source sufficient to let it be commercial. After their separation, the original developpers of DivX continued their work under the name XVID. Quote: XviD (guess where the name came from ...) is a good opensource MPEG4 codec though, which, i think, also supports DivX. Information on the project and sourcecode downloads can be found at: http://www.xvid.org/ Yes, it does support DivX. So the best you can do, is use the XVID source to support videos, together with some open-source MP3-decoder. 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