3． About the functions of Cinepak for SEGASATURN

3.1 Seamless branching

If you want to continuously play a movie that has been split into multiple parts, or if you want to interrupt the movie being played and branch to another movie (branch playback), use the stream system to perform seamless branching (seamless branching is not supported in the file system). (not supported). Seamless branching is achieved by moving the pickup of the CD drive to the next movie to be played while playing movie data that has been read ahead in the CD buffer. Therefore, a certain amount of movie data must be stored in the CD buffer, and the transfer rate of movie data should not exceed 290KB/S (in double speed mode). If the movie data transfer rate is 290KB/S, when the first movie is played for 15 seconds, about 150KB of movie data will be accumulated in the CD buffer, and it will take about 0.5 seconds to play the next movie. There will be a margin. If you can load the next movie's header and first sample data during this margin, you can do a completely seamless branch.

●Continuous playback using seamless branch 1

Figure 3.1 originally shows one movie divided into three parts. By registering movie B as the next movie to play while playing movie A (CPK_EntryNext function), movie B will automatically start playing seamlessly after movie A finishes playing. Movie C is also registered in the same way as movie B is being played. This allows the three split movies to be played exactly the same as the one movie before splitting.

Figure 3.1 Continuous playback 1

●Continuous playback using seamless branch 2

Figure 3.2 shows the case where either Movie B or Movie C is played after Movie A has finished playing. Similar to continuous playback 1, the branch destination is determined while the data necessary for branching remains in the CD buffer, and the next movie to be played is registered (CPK_EntryNext function). Now, after Movie A finishes playing, Movie B or Movie C will start playing seamlessly.

Figure 3.2 Continuous playback 2

●Branch playback using seamless branches

Figure 3.3 shows a case where playback of movie A is interrupted and branched to movie B or movie C. When a branching condition occurs during movie A playback, register the next movie to play (CPK_EntryNext function) and then forcefully switch the playback movie (CPK_Change function). Now, after movie A is interrupted, movie B or movie C will seamlessly start playing.

Figure 3.3 Branch playback

Note

• For movies that perform seamless branching, the sound content (sampling rate, quantization bit number, number of channels) and frame rate must be the same.
  
• Place movies that will be seamlessly branched as close together as possible on the CD-ROM. Also, place them in the order of branching from the inside of the CD-ROM to the outside.
  
• Seamless branching is not available for multimovie playback.

3.2 Multi-movie playback

Cinepak for SEGASATURN can play up to 4 movies simultaneously on the screen. Figure 3.4 shows an image of multi-movie playback. To create a multi-movie movie, follow the same steps as when creating a single regular movie. Sounds can be played independently for each movie at the same time (or you can play only the sound for the movie the user has selected and turn down the volume for other sounds), or you can have just one sound. You can also play other movies with only images.

Multimovie has the following formats:

• Channel interleave multiple movies onto CD and play from CD simultaneously

• Play movies in memory and movies on CD at the same time

• Load multiple movies into memory and play them simultaneously

Figure 3.4 Multimovie playback

Note

• If you want to channel interleave multiple movies on a CD, please specify the data rate (bit rate) of each movie accurately and interleave them (for details, refer to the virtual CD manual).
  
• If multiple movies each have sound, please lower the sampling rate (about 11KHz).
  
• Seamless branching cannot be performed from multi-movie playback.

3.3 Superimpose

Using a movie shot with chroma key, you can superimpose the subject onto another still image or the background of the movie. Superimposition is achieved by making the specific color specified in MovieToSaturn_J transparent when decoding it on SEGASATURN. Therefore, the background you want to make transparent must be a single color. Superimposed movies can be used with or without sound.

Figure 3.5 Superimpose

To superimpose, use Adobe Premiere's Color Replacement filter or Transparency settings. (Please refer to the Adobe Premiere manual for details on "color replacement" and "transparency settings")

●For “color replacement” filter

1. For example, if the movie was shot against a blue background, select the blue background as the target color. Next, set the replacement color to "red = 0, green = 65536, blue = 0" and replace it with pure green. Use the similarity slider and repeat replacement to make the background a pure green color. At this time, be careful that the replacement destination color is not included in the superimposed subject. If it is included, pure red, white, black, etc. can be used instead of green.

2. Once the color replacement is complete, compress the movie using Cinepak.

3. Next, when converting with MovieToSaturn_J, click the "Options" button, select chromakey processing, and enter the color value to be keyed out (Figure 3.6). If the replaced color is pure green, enter "Red=0, Green=255, Blue=0" and convert to SEGASATURN format.

●For “transparency setting”

Place a blue-backed movie on the super track of the construction window, and place a blue-colored still image to be keyed out on the A track. After selecting the Super Track movie, open the transparency settings dialog and select Chroma as the key type. Use the Similarity slider to adjust the background color to make it look nice and transparent. Now you can create a movie with the A track matted.
After that, perform steps 2 and 3 in the same way as for "color replacement".

Figure 3.6 MovieToSaturn_J options dialog

Note	For superimposed movies, the edges of the movie will change from the specified color due to Cinepak compression, making it impossible to key out the movie clearly. In this case, use the CPK_SetKeyOutRange function to adjust the range of colors to key out.

3.4 Keyframe pose

●About key frames

There are two types of movie compression: spatial compression, which compresses data within a frame, and temporal compression, which compresses parts that are unchanged from the previous frame by not having data. Generally, frames that have been compressed in time are called differential frames, whereas frames that have only been compressed in space are called key frames.
Cinepak is a compressor that supports differential frames, and can perform time compression by specifying keyframes during compression. For example, if you set "keyframe every 30 frames", it will consist of 1 keyframe and 29 difference frames (because the Cinepak compressor may automatically insert keyframes, it will actually consist of 1 keyframe and 29 difference frames. (There is no guarantee that there will be a keyframe every 30 frames.) Differential frames have a type of blocking phenomenon in which the time-compressed portions appear to be blocks. If you compress without specifying a keyframe, only the space of each frame will be compressed and there will be no difference frames.

Figure 3.7 Relationship between key frames and difference frames

●Key frame pose

The Cinepak library's pause function (CPK_Pause function) provides parameters for specifying immediate poses and keyframe poses. If you specify a keyframe pose, it will naturally not pause until the keyframe appears after starting the pose. Therefore, if you specify a key frame every 1 second, you will have to wait up to 1 second after starting the pause. This is to ensure synchronization with the sound when unpausing. To avoid this, do not specify keyframes when compressing Cinepak, or shorten the interval between keyframes.

3.5 Still image playback

By loading the movie data into memory in advance and decompressing the specified frame (CPK_DecordeFrame function), you can use the movie frame data as a still image.

Figure 3.8 Flow of still image playback

Note

• For still movies, please compress them with Cinepak without adding sound.
• The frame rate when compressing Cinepak is arbitrary (meaningless).
• Never specify keyframes when compressing with Cinepak.
• All still image movies must be loaded into memory. If the frame size is full screen, it would be appropriate to make the movie file about 10 to 20 frames.