The document provides an extensive overview of multimedia transcoding techniques used in streaming digital content, emphasizing the necessity for effective video format adjustments based on device capabilities and network conditions. It discusses various architectures and classifications of transcoding, the significance of quality of experience (QoE), and challenges faced in maintaining user experience during video transmission. The paper highlights the shift towards transactional transcoding to optimize video delivery for diverse devices and improve operational efficiency.

1. Poster Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
An Overview on Multimedia Transcoding Techniques
on Streaming Digital Contents
Shakti Awaghad1 and Sanjay Pokle2
1
Research Scholar, Dept of Electronics & Communication Engineering., G. H. Raisoni College of Engg, Nagpur, India
Shakti_awaghad@yahoo.co.in
2
Professor & Head, Dept. of Electronics & Communication Engineering, R.C.O.E.M, Nagpur, India
sanjaypokle@yahoo.in
cessing is done (like adding logo or commercial to the video).
This process requires a high computational power and data
flow. During the transmission of the videos there are limitations of the network bandwidth available and problems concerning transmission errors. Some techniques [2] allow recovery of the video from errors occurred on the end-user
side or during transmission. On the end-user side there are
different kinds of devices. Depending on the device limitations are in processing power, display resolution, codecs
available, etc. Transcoding is used in various multimedia
systems like conferencing, telemedicine, education and military. In these systems, audio and video needs to be delivered
smoothly without interruptions. Quality of user experience
must meet the prescribed level of quality of experience for
that system.
The paper presents an exclusive review of the
phenomenon for multimedia transcoding. Section 2 highlights
the significance of using transcoding process in multimedia.
Section 3 discusses about illustrating architectures of
transcoding followed by classification of transcoding in
Section 4. The past research work and conclusions is
discussed in Section 5.
Abstract— The current IT infrastructure as well as various
commercial applications are directly formulated based on
deployment in multimedia system e.g. education, marketing,
risk management, tele-medicines, military etc. One of the
challenges found in using such application is to deliver
uninterrupted stream of video between multiple terminals
e.g. smart-phone, PDAs, laptops, IPTV etc. The research shows
that there is a stipulated need of designing novel mechanism
of bit rate adjustment as well as format conversion policy so
that the source stream may stream well in diverse end devices
with multiple configuration of processor, memory, decoding
etc. This paper discusses various eminent points from
literature that will throw better highlights in understanding
a schema of direct digital-to-digital data conversion of one
encoding to another termed as transcoding. Although
multimedia transcoding has covered more than a decade in
the area of research, but unfortunately, there is a huge tradeoff between the application, service, resource constraint, and
hardware design that gives rise to QoS issues.
Keywords-component; M ultimedia Transcoding, Video
Transcoding, data-format conversion.
I. INTRODUCTION
The amount of video content on the Internet has rapidly
grown during the last decade. Introduction of video services
such as YouTube has enabled users to generate their own
content and upload it to online video services. In 2007 more
than 500.000 user-generated content was uploaded daily on
those video services [1]. This created a huge amount of multimedia content which needs to be available to users on the
Internet. All the multimedia content needs to be transformed
into right format for every user. For example, someone is using a desktop computer who wants to watch a high definition
video or users who wants to watch video on their mobile
phone with a small screen needs video that is optimized for
their low resolution screen and limited network bandwidth.
This means that every video must be transcoded into the
right resolution, frame rate, bit rate and codec. In multimedia
system there should be an original video recorded by a camera or created on the computer and encoded into a compressed
format. After that the video is uploaded onto an Internet
server where the whole transcoding process begins. When a
user requests a video, server needs to transcode the video
into the desired format and send it to the user. The video
from the server is transcoded into a format with desired resolution, bit-rate, frame-rate, codec, and all other specific pro© 2013 ACEEE
DOI: 03.LSCS.2013.2.42
II. SIGNIFICANCE
Quality of experience is used to measure the real efficiency of the transcoding algorithms and video coding algorithms in general. User experience is dependent on both the
video and audio quality of the streamed content. Depending
on the content type (news shows, sport games, movies, etc.)
people react differently to the proportion of video/audio quality. In particular lower video quality is acceptable in a news
show if audio is of good quality. Opposite to that lower audio
quality with good video would be acceptable for some sport
games [3]. Delay time is also important factor that needs to
be carefully planned not to degrade the QOE. After requesting a stream from a server and defining its capabilities, end
user has to wait some time for the transcoding process to
begin and for the transmission of the content to his device.
With some perceptual tricks like displaying the channel logo,
waiting time can be shorten, but just perceptually [4].
Transcoding algorithms should be able to provide a lower
bandwidth video when degradation occurs on the available
network bandwidth. This will help from video being stopped
and it will be played at lower quality. Unfortunately this approach won’t help if the bit-error or jitter is high. Researches
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2. Poster Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
of QOE for the standard devices like desktop computers,
video consoles and television has been done but further
researches is needed to see the difference concerning mobile
devices.The first and most important challenge in the context of a video conferencing is to provide transcoding on the
fly with real-time speed and without any interruption of video
flow [5], [6]. There are three basic requirements in transcoding
[7]: 1) the information in the original bitstream should be
exploited as much as possible; 2) the resulting video quality
of the new bitstream should be as high as possible, or as
close as possible to the bitstream created by coding the original source video at the reduced rate; 3) in real-time applications, the transcoding delay and memory requirement should
be minimized to meet real-time constraints. A video transcoder
can provide several functions, including adjustment of bit
rate and format conversion. We illustrate these functionalities
and their classification in Fig. 1.
from normal video to a video containing only the region of
interest.
III. UNDERSTANDING TRANSCODING ARCHITECTURES
The most straightforward transcoding architecture is to
cascade the decoder and encoder directly. In this architecture,
the incoming source video stream (Vs) is fully decoded, and
then re-encoded the decoded video into the target video
stream (VT) with desirable bit-rate or format, with no
degradation in the visual quality due to transcoding. Spatialdomain transcoding architecture (SDTA) that can perform
dynamic bit-rate adaptation via the rate-control at the encoder
side. This architecture is flexible since the decoder-loop and
the encoder-loop can be totally independent of each other
(e.g., they can operate at different bit-rates, frame-rates,
picture resolutions, coding modes, and even different
standards). This architecture is drift-free, but its
computational complexity is high for real-time applications.
TABLE I. ACRONYM
VLC
VLD
Qs-1
Qr
Qr-1
DCT
IDCT
R
ME
MC
Figure 1 Different Transcoding techniques
USED
Variable Length Coding
Variable Length Decoding
Inverse quantization of the source
Quantization of the target video
Inverse quantization of the source
Discrete Cosine Transform
Inverse DCT
Reference Frame
Motion Estimation
Motion Compensation
Exploiting the structural redundancy of the architecture
and the linearity of the DCT/IDCT, structurally simpler but
functionally equivalent frequency-domain transcoding
architecture is possible, which can be further simplified as
shown in Fig. 2.
Homogeneous transcoding performs conversion between
video bitstreams of the same standard. A simple technique to
transcode a video to lower bit rate is to increase the quantization step at the encoder part in the transcoder [8], [9]. Spatial
resolution can be done in a number of ways (see Fig. 3) [10].
One possibility is to transcode from normal video to a video
containing only the region of interest. Fig. 4 illustrates that a
transcoder can down-sample a scene to the object of interest
(determined through meta information). This may be done
using some meta information. In subsampling, filtering and
pixel averaging to reduce spatial resolution [10] problems
arise when passing motion vectors directly from the decoder
to the encoder. Thus, motion vectors need to be refined.
Frame-rate conversion is needed when the end-system supports only a lower frame-rate. With dropped frames, the incoming motion information is invalid because they point to
the frames that do not exist in the transcoded bitstream. A
heterogeneous video transcoder provides conversions between existing and future video coding standards. It provides syntax conversion between these standards. Further, a
heterogeneous video transcoder may also provide the
functionalities of homogeneous transcoding. Transcoding
Figure. 2. Frequency domain transcoder architecture (FDTA)
may include additional functions such as error-resilience and
In this architecture, only VLD and inverse quantization
logo or watermark insertion. These functions will be described
are performed to get DCT value of each block in the decoder
in the paper subsequently.One possibility is to transcode
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© 2013 ACEEE
DOI: 03.LSCS.2013.2. 42

3. Poster Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
end. At the encoder end, the motion compensated residue
errors are encoded through re-quantization, and VLC. The
reference frame memory in the encoder end stores the DCT
values after inverse quantization, that are then fed to the
frequency-domain MC module to reduce drift error. This is
referred to as frequency-domain transcoding architecture
(FDTA).
allow the problem of creating content to be separated from
the problem of creating different presentations. Dynamic
transcoding shown below as figure.4. consists of a set of
techniques for tailoring the information generated for a user
to match the specific presentation requirements of a given
user on a given device on a given level of network service.The
mechanism used by Dynamic Transcoding can be used across
a wide variety of content for a wide variety of devices, they
reduce the overall development and maintenance costs of
Web applications.
IV. CLASSIFICATION
Transcoding is process of decoding video from some
format to usually uncompressed format and encoding it to
desired format. For example during transcoding an MPEG-2
video would be decoded to RAW format and then encoded
into H.264 format. This process is an intensive computation
process for server processor. Most intensive part of
transcoding is motion estimation. This is because during
motion estimation we must find how some blocks of picture
move from one frame to another.
A. Types of Transcoding
The proliferation of wireless devices with very different
form factors multiplies the costs associated with Web
applications. Different devices require pages to be presented
in different markup languages, such as HyperText Markup
Language (HTML), compact HTML (including a version
called imode that is popular in Japan), Unwired Planet’s
Handheld Devices Markup Language (HDML), Wireless
Markup Language (WML), and VoiceXML. There are two
main approaches to handling the need to present the content
delivered by an application differently in different
circumstances, for different
devices, and for different levels of network service.
Static transcoding: With static transcoding of static
content, different versions of the same content are produced
by a designer as shown in figure.3, generally using various
studio tools, and stored in the file system of the Web server.
With static transcoding of dynamic content, either different
versions of the application are provided or the application
contains logic that produces different versions of the content.
Figure 4 Dynamic Transcoding
Spatial And Temporal Transcoding: The heterogeneity of
communication networks and network access terminals often
demand the conversion of compressed video not only in the
bit rates, but also in the spatial/temporal resolutions. One of
the challenging tasks in spatial/temporal transcoding is how
to efficiently re-estimate (or map) the target motion vectors
from the input motion vectors. Many works on the motion reestimation for spatial transcoding consider the simple case
of 2 1 downscaling. For transcoding with temporal resolution
changes, due to the frame dropping, one has to derive a new
set of motion vectors that do not exist in the input video.
Video services used transcoding in a way that they pretranscoded an original video and stored it in one or more
formats that they later used for streaming to end user. Lately
number of different formats of multimedia streams requested
by users is growing with number of new devices having
different capabilities (in terms of resolution, processing power
and network bandwidth). These trend increases number of
different files needed for every single multimedia content.
Increase in number of transcoded files requires more
processing power for transcoding and more storage space
for storing those files. Even doe storage space is taken as a
low cost resource, this increase in space is significant and
requires new ways of transcoding. IDC proposes a different
approach in transcoding called transactional transcoding [1].
In transactional transcoding multimedia content is transcoded
when there is a need for transcoding. Original multimedia
content is kept only in original format or some format that is
more appropriate for transcoding. When a transcoding
request comes from the end user, transcoding starts. User
can request which format of multimedia he needs. The
transcoding technique in this literature is briefly classified
into two phases as illustrated below:
1.Homogeneous Video Transcoding: Homogeneous
transcoding performs conversion between video bit streams
of the same standard. A high quality source video may be
Figure. 3 Static Transcoding
The primary disadvantage of static transcoding is the
number of different pages and applications that have to be
created, tested, organized, and maintained. As the number of
devices increases, the burden of hand generating different
versions of each application or page for different
presentations will become onerous.
Dynamic transcoding: Dynamic transcoding promises to
© 2013 ACEEE
DOI: 03.LSCS.2013.2.42
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4. Poster Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
Figure.5 Heterogeneous video transcoder
transcoded to a target video bitstream of lower quality, with
different spatial/temporal resolutions, and different bit rates.
Some of the research issues found in this type of transcoding
techniques are reducing bits with fixed resolution, spatial
resolution reduction, temporal resolution reduction, and
transcoding between multiple and single Layers
2. Heterogeneous Video Transcoding: A heterogeneous
video transcoder as shown in figure.5, provides conversions
between various standards, for instance, MPEG-2 to H.263
transcoder, MPEG-2 to MPEG-4 transcoder, H.263 to MPEG4 transcoder, etc.
In this architecture, syntax conversion (SC) is needed to
convert the syntax of source video to that of the target video.
A higher resolution decoder decodes the incoming bitstream.
The extracted MVs are then post-processed according to the
desired output encoding structure, and if required, they are
properly scaled down to suit the lower spatial-temporal
resolution encoder. In case post-processing is not sufficient,
the extracted MVs are refined to improve the encoding
efficiency. The decoded pictures are accordingly downsampled spatially or temporally, and the down-sampled images
are encoded with the new MVs. Since the incoming MVs are
re-employed, and other encoding decisions, such as
macroblock types can be extracted from the incoming
bitstream, the architecture of this transcoder can be further
simplified.
the multimedia. Some videos might still be streamed in the
old way by pre-transcoding, but majority of videos will need
to be streamed in a novel way of transactional transcoding.
Transactional transcoding will allow video to be optimized
for the end user to gain the best possible quality of experience.
Also it will provide the means of extra monetization features
like delivering ads targeted using location based services.
REFERENCES
[1] G. Ireland and L. Ward, “Transcoding Internet and Mobile
Video: Solutions for the Long Tail”, IDC, 2007
[2] L. Superiori, O. Nemethova, M. Rupp, “An H.264/AVC Error
Detection Algorithm Based on Syntax Analysis”, In: A. M. A.
Ahmad and I. K. Ibrahim, “Multimedia Transcoding in Mobile
and Wireless Networks”, Information Science Reference,
London, 2009, pp. 215 – 234.
[3] H. Knoche and M. A. Ssse, “Getting the Big Picture on Small
Screens: Quality of Experience in Mobile TV”, In: A. M. A.
Ahmad and I. K. Ibrahim, “Multimedia Transcoding in Mobile
and Wireless Networks”, Information Science Reference,
London, 2009, pp. 31-46.
[4] N. Roma and L. Sousa, “Insertation of irregular-shaped logos
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[5] G. Keesman, R. Hellinghuizen, F. Hoeksema, and G. Heideman,
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V. CONCLUSION
Multimedia content is taking a primary role in Internet.
From the beginning of Internet when text with small amount
of images was the leading element, in this decade primary
role is being taken by multimedia content. Progress has been
empowered by higher network speeds and better processing
power of end user devices. Also development and outspread
of mobile devices capable of playing multimedia opened new
approaches to video experience. All this together with vast
amount of user generated videos being uploaded and watched
every day is contributing to research in the field of
transcoding. To keep up with the increasing amount of user
generated videos and diversity of devices for watching
videos, providers will need to change the way of transcoding
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DOI: 03.LSCS.2013.2. 42
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