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Speech Coding for Wireless Communications
Published in Jerry D. Gibson, Mobile Communications Handbook, 2017
When different codecs are used in different but interconnected networks, or when the speech signal must be decoded at network interfaces or switches, the problem of tandem connections of speech codecs can arise. The term “asynchronous tandeming” originally referred to a series connection of speech coders that requires digital to analog conversion followed by resampling and reencoding. Today, and within the context of this chapter, tandeming refers to where the speech samples must be reconstructed and then reencoded by the next codec. Tandem connections of speech codecs can lead to a significant loss in quality, and of course, incur additional delays due to decoding and reencoding. Another possible approach to tandem connections of different speech codecs is to map the parameters of one codec into the parameters of the following codec without reconstructing the speech samples themselves. This is usually referred to as transcoding. Transcoding produces some quality loss and delay as well. Tandem connections of speech codecs are often tested as part of the overall codec performance evaluation process.
Media Systems Integration
Published in Al Kovalick, Video Systems in an IT Environment, 2013
The more choices MXF allows for (and there are plenty), the less likely that any two-party transaction will succeed without some format manipulation. The gateway performs at least four different kinds of operations per Figure 7.12: Case 1. MXF import/export is compatible and compliant to both sides. In this case the GW does no format changes. This is the trivial case.Case 2. MXF is compliant on both sides, but the MXF essence layers are not compatible. For example, the GW may need to transcode from MPEG to DV. Another possible change is from OP-3a to OP-1a. This step may cause quality degradation and delay the transfer due to slow transcoding.Case 3. The external wrapper is not MXF compliant (may be AVI), but the essence, say DV, is compatible. The GW unwraps the DV and rewraps it under MXF. This is a fast transaction, with no quality loss, but metadata may be lost when going from MXF to a non-MXF format.Case 4. The external wrapper layer is not MXF compliant, and the essence layer is not compatible. This is the worst case and costs in quality and time. Avoid if possible.
Multimedia conferencing
Published in Steve Heath, Multimedia and Communications Technology, 1999
The immediate problem with transcoding is the additional processing that is needed and the time delay involved. With an MPEG 1 bitstream and its future and past motion estimation algorithms that require access to past and future frames, a considerable delay is involved. This is not necessarily a problem with an answering machine: the delay can be tolerated and the transcoding between the H.320 data and the recording MPEG1 format performed after the call has been ended to reduce the processing power needed. If the call involves any interactive activity, e.g. a live voice commentary, with the MPEG1 video describing the scenes, the problems in synchronising the delays become immense: the transcoding takes time and therefore the audio must be delayed to compensate. This incurs another delay in the H.320 process and the result is a call, where the delay and synchronisation reduce the intelligibility of the call.
An investigation on adaptive HTTP media streaming Quality-of-Experience (QoE) and agility using cloud media services
Published in International Journal of Computers and Applications, 2021
Selvaraj Kesavan, E. Saravana Kumar, Abhishek Kumar, K. Vengatesan
Cloud encoding/transcoding services are provided by cloud-based companies to which upload source video files and set appropriate parameters to get the output encoded/transcoded media. Transcoding service has the ability to take multimedia content from a live source and to transcode it to the required content output format with given specifications (bit rate, quality) as per the client player request.