576i#PAL speed-up

PAL acceleration (English PAL speed -up ) refers to a technique of standards conversion, which is used to convert movies that are usually produced at 24 frames per second in the PAL format instead of 25 frames or 50 fields operates per second.

When converting movies ( 24 frames / s ) to the NTSC format ( 29.97 frames / second or 59.94 fields / s ) is also a change of the playback speed necessary; this is described in the 3:2 pull-down method.

Media and formats, which can save movies at 24 frames per second, such as the Blu- ray Disc, which are not naturally affected. In television, the problem remains, however, also largely preserved with HDTV, as the transmitter, the PAL (analog) and SD ( digital) have sent at 50 Hz, which continue even in HD.

• 2.1 pitch
• 2.2 TV series on Blu- Ray Disc
• 2.3 Special Case Music Video
• 2.4 PAL acceleration and interface version

Technical Background

Predecessor: standards conversion to NTSC

Historical predecessor of PAL acceleration is still used 3:2 pulldown for conversion of conventional films (24 frames / sec ) in the U.S. television standard NTSC ( 29.97 frames / second or 59.94 fields / s ).

This conversion from the silver screen in the NTSC standard is done by the film images by a slowdown to a rate of 23,976 B / s alternately three and two fields occupy ( 2:3 pull-up ); However, this does not change the running speed of now 23,976 B / s, but there are images repeated after a predetermined rhythm or divided into different fields to come on for the NTSC television standard required 59.94 fields / s.

A disadvantage of this method is the occurrence of jerky movements acting in slow panning - is an advantage, however, the almost correct playback speed.

PAL acceleration

For PAL has 25 frames per second conversion using drop -down would be far less practical, since the numbers 24 and 25 ( other than 23.976 and 59.94 ) have no common divisor; Therefore, the disadvantage of accelerated playback in favor of a simple 1:1 conversion method is accepted.

The so-called PAL acceleration now the current with 24 B / s starting material for the PAL standard is simply played back at 25 frames per second, the frame rate is increased to the specified in the standard 25 frames per second. Due to the acceleration typically occurs a pitch change of about one -half to one semitone, which is compensated by the acceleration in recent times by artificially lowering the pitch of the original sound frequency (see also the following section pitch).

Due to the change of the frame rate that the default is to convert the different television standards, a movie automatically has ( absolute Identical content once assumed) a PAL by about 4% (100/ 24 * 25) shorter and NTSC by 0.1 % (100/ 24 * 23,976 ) longer run length.

A comparison of the run length of a film in its NTSC or PAL variant is calculated in accordance with 23.976 frames per second, or 95.904 %. Examples:

• The running time of a movie changed from 120 minutes to 96% of the term, ie 115 minutes and 12 seconds.

• Conversely, a movie on a PAL DVD with a running length of 120 minutes in the original total of 125 minutes.

Confines

A PAL - acceleration is not in question, when the starting material

• From an NTSC video camera comes = 59.94 fields per second
• Of a progressive NTSC source originates = 29.97 frames per second

In this case, the images are in the standard conversion distributes time accurately weighted on the 50 fields per second the PAL format (mostly using Deinterlacing either by interpolation, ie calculation of the gaps, or by blending, ie merging of the two fields, on both see Deinterlacing ).

In the standard conversion from NTSC to PAL also a slowdown of 29.97 to 25 B / s would be possible, but would require extensive post-processing of the clay next to a much larger difference in the speed of visible movement, since in a 2 hour movie almost 24 min run-length difference arise. The difference in the actual speed would be here with about 19.88 % ( 29.97 / 25 ) is far greater than in the 0.1 to 4 % under the previous standards of 24 ( film), 23.976 ( pull down for NTSC ) and 25 B / s ( PAL). Therefore, in the standard conversion from NTSC to PAL is no such slowdown.

Converts to the NTSC to PAL source material as if it had 30 B / s instead of the actual 29.97 B / s, a simple converting the images is possible. In a 2-hour film gives a Tonverkürzung by 7.2 s, ie the sound can not be simply assumed.

Pulldown for PAL

It also happens that a TV station wants the original length of a film or series without PAL acceleration. Then, similarly as in NTSC, worked with mixing images, however, this method is not 3:2 pull-up, but 2:2:2:2:2:2:2:2:2:2:2:3 - pull-up ( 11 * 2 3 = 25 pull- ups). ( Full screen 24 > fields 48, 49, 48 frame 12 > fields 23, 24, 23 ) where every second is the field with the even line of frame 12 and the field with the even scan lines of frame 24 as the third field repeatedly. The copy from field 23 to field 25 and the copy from field 48 to field 50 is advantage is that the original speed and pitch can be maintained without further processing.

A disadvantage is that by this method panning the camera twice the image short stops in the second, the Ruckeleffekt but lower than in the NTSC -2 :3- pull-up. In video movies added that before the beginning of the 1990s did not exist the technical possibility for productions to make the pull-down to reverse ( inverse telecine ). Therefore, the blending often provided the only way dar.

Problems

Pitch

Technically the film at 1/24 ( 4.17% ) is played faster and also the sound is increased by 1/24, which is about 71 cents. This may strike people who have perfect pitch - such people take for example the difference of film music in comparison with, for example, a CD as a " tune in to " true, as the moving all sounds " off the mark ". The acceleration of the image is hardly perceived by humans, just as the pitch change the language if the theatrical version the viewer is not known.

To work around the pitch problem, partly in series and very rare in films a pitch correction is performed by the digital time stretch method. A disadvantage here is that the use of inferior converter software (eg in video editing software ) sound artifacts in the form of distortion and tiny sound interruptions occur. Such artifacts are more significant when attempting to change the velocity or barrel length while maintaining the pitch ( corresponding settings with inferior conversion algorithm found, for example in Adobe Premiere Pro). Basically, it is therefore recommended to make the digital pitch correction in specialized audio programs. The simple change of the sound is not the same as the distortion artifacts of an inferior converter.

In synchronized television productions are identified:

• Synchronization before the PAL Acceleration: The tessitura of the voice actors is also raised. This is often the case with old productions of the case in which, after the first performance again a new, better-quality standards conversion was made. Mostly this is done in conjunction with a DVD release.
• Synchronization after the PAL acceleration: Only the music and sound tracks are lifted. This type of processing is increasingly used in new productions, more recently, partly in the cinema (if there is not played at 24 frames / s).
• New scoring after PAL acceleration: music, noise and synchronous tracks retain their natural sound. This type of processing is increasingly used in ( U.S. ) series that are shown on TV.

TV Shows on Blu- Ray Disc

TV series that were produced at 24 frames / second, are generally accelerated for the European market first to 25 frames / second and then synchronized. Was in the conversion no pitch correction, the music and sound tracks, the synchronous gauge are increased in pitch, do not. On a Blu -ray Disc, the synchronized soundtrack is slowed back down to 24 frames / second. The result is that the music and sound tracks sound back to normal, however, the sync track sounds too deep.

While the problem of different pitches retrospectively by a pitch correction can be corrected only the voice track, a correction of distortion artifacts due to inferior converter is as good as impossible.

To circumvent these problems, the sync track should either be basically created at 24 frames / second ( see synchronization before the PAL acceleration), or at any speed conversion done a quality pitch correction to maintaining the original pitch.

Special case Music Video

In music videos, which are produced in the U.S. space on film, the cut is usually after sampling in the NTSC standard; as in television series, a film copy is sent to Europe for a PAL scanning mostly. With music videos from movie soundtracks with excerpts from the corresponding movie from it, however, results in a rights issue, as figures for the music video no copy or Abtastrechte for a total copy of the feature film, and a separate copy and PAL sampling of individual film scenes were mostly too expensive.

In practice, one makes do mostly with a standardized film scanning of pure music video material to PAL, then the previously scanned with the NTSC and PAL usually inferior to the converted movie scenes cut together. The disadvantage consists in an unsightly ~ 10 Hz Rucklereffekt as well ( due to the lower lines of resolution of NTSC) a basic blur in movie scenes in the music video.

PAL acceleration and interface version

On the question of whether a DVD release is cut or uncut, the PAL acceleration often creates confusion. Comparing only the run- time information collected from Kino-/NTSC-Fassung and PAL version of a film is formed on the basis of about four percent difference quickly the impression of a substantive reduction. In fact, this is but might not even exist. To avoid having to make any detailed content direct comparison can simply a conversion of the Kino or NTSC to be made the PAL runtime.

To counter (also market economy detrimental ) confusion, exhibited for example, the company Kino world on the director's cut DVD cover of the movie Saw explicitly states that its PAL runtime of about 99 minutes, about 103 minutes long NTSC or Theatrical version corresponds fully content.