Uninterrupted playback

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Seamless playback (also gapless playback or English gapless playback ) refers to the continuous playback of related consecutive audio files , for example, on a portable MP3 player .

In the score, pieces that should follow one another without a break are notated with Attacca ; a popular example is the transition from the 3rd to the 4th movement in Beethoven's 5th Symphony . It now depends on the publisher whether these are copied onto the CD as a single track or separately. Only in the latter case can a problem arise during playback.

Without interruption-free playback, interruptions between the tracks are always perceptible, which is perceived as annoying when playing corresponding pieces of music or with live albums with the audience continuously listening .

This article primarily deals with problems of uninterrupted playback, which are based on the definition of the underlying file format (e.g. MP3 ) and are therefore based on principle. In addition, there are often deficiencies in the playback software or firmware of the playback device , which lead to uninterrupted playback, even if the underlying media file format actually meets the requirements for uninterrupted playback.

Weaknesses in the file formats

The aforementioned pauses are not part of the original recording, but arise from the fact that audio data formats are based on blocks of fixed duration, the so-called frames. If an audio recording ends before the end of the last frame while creating such a file, the rest of the frame is filled with silence. The duration of a frame is in the range of tens of milliseconds, for example for MP3 files with 44,100 samples per second about 26.1 ms, so that the additional pause is almost as long in the worst case. In addition, the coding process creates a delay that leads to a pause at the beginning of the performance; it is roughly in the region of half a frame duration.

The first audio codec to support gapless playback is ATRAC . The proprietary format was originally developed by Sony exclusively for the MiniDisc . Newer audio formats such as Vorbis , Musepack , Speex and Windows Media Audio as well as all lossless compression methods (e.g. FLAC ) support Gapless Playback by default by storing information about the exact length of the audio data and the encoder delay in addition to the bare audio data .

Earlier audio formats were not yet capable of uninterrupted playback. These include the first MP3 codec from the Fraunhofer-Gesellschaft and AAC . However, there are extensions: In the open source encoder LAME for the MP3 format, a function is implemented that adds information to the generated files for gapless playback. Suitable playback devices or software, for example foobar2000 , VUPlayer or mpg123 , can use this information to remove the filler data from the last frame and compensate for the coding delay, thus enabling gapless playback. This method is not covered by the MP3 standard. The necessary information is stored in a frame at the beginning of the file, which is prepared in such a way that it is decoded into silence. Players who cannot cope with this extension will sometimes play back this frame, which increases the interruption.

Weaknesses in the playback software or firmware

A distinction must be made between the facts mentioned above and the additional pauses in some MP3 players . These arise, for example, from inadequate buffer management, i.e. H. the next track is loaded into memory too late to play.

On the hardware side, very few devices - whether mobile players or DVD players from the home video sector - offer a solution for audio formats that do not support uninterrupted playback by default. Some models support gapless playback by using alternative firmware such as Rockbox . The same applies to the TrekStor Vibez, which, however, belongs to a higher price range. Cheaper devices often only have a hardly usable dissolve function. The seamless playback of AAC and MP3 files on an iPod is realized by processing in the iTunes software used for the transfer.

Compact discs

A similar effect occurs with burned audio CDs if the CDs were written using the Track-At-Once method.

Web links

supporting documents

  1. ↑ gapless playback. In: Hydrogenaudio Knowledgebase. HAK Community, January 12, 2015, accessed June 7, 2015 .
  2. ↑ MP3. VBRI, XING, and LAME headers. In: Hydrogenaudio Knowledgebase. HAK Community, January 29, 2013, accessed June 7, 2015 .