Beitrag (Sammelband oder Tagungsband)
J. Bialkowski, M. Menden, Marcus Barkowsky, A. Kaup
A Fast H.263 to H.264 Inter-Frame Transcoder with Motion Vector Refinement
Picture Coding Symposium (PCS) 2004, San Francisco
Video transcoding techniques supply interoperability of a great variety of devices that can be connected by various communication networks with different data rate requirements. Particularly inhomogeneous video transcoding is the conversion of an existing video bitstream from one standard into a bitstream of another standard, for example the conversion from H.263 data into H.264 data. It may also include parameter adaptations such as bitrate or frame rate reduction. In this work, we present a low-complexity transcoder design for transcoding Interframe macroblocks from H.263 to H.264. The large complexity reduction comes from reusing motion vectors of the input bitstream and from the fact that only a subset of all possible H.264 coding parameters is used. The selection of these parameters is based on statistical investigations of encoded H.264 parameters from a full parameter search on decoded H.263 sequences. Our approach leads to small rate-distortion losses compared to the full parameter encoder below 0.5 dB at comparable data rates, but the computational complexity reduction is over 98% for finding a suitable macroblock decision. Compared to simply copying the motion vectors without post-processing, the rate-distortion gain of our approach is up to 2 dB at equivalent rate.
Subjective and Objective Video Quality Measurement in Low-Bitrate Multimedia Scenarios
In recent years, many distribution channels for low-bitrate video transmissions were setup. The parameter settings for the encoder, the transmission
channel, the decoder and the playback device are manifold. In order to maintain customer satisfaction, it is necessary to carefully select and continuously
tune those parameters and to monitor the resulting video quality at the receiver. This thesis considers the quality measurement by a human observer
and by an automated algorithm.
In the first part of the thesis, several subjective tests are performed in
order to draw conclusions about the choice of transmission parameters. The
experience gained from those experiments led to three psychophysical experiments that focus on isolated aspects of the video quality in lossless or
lossy low-bitrate transmissions. Three distinct algorithms are deduced from
the subjective experiments which deal with the temporal aspects. First, the
visibility of artifacts is modeled when the viewer only has a short period
of time for the examination. Second, the influence of transmission outages
is modeled: The video playback may pause and content may be skipped if
retransmission is not possible. Third, the visual degradation introduced by
a reduction of the frame rate is modeled.
The second part of the thesis is dedicated to the objective measurement.
It is assumed that the reference video sequence is available for comparison
with the degraded sequence. Because the performance of the automated
measurement depends strongly on the correct alignment of the degraded
signal to the reference signal, various algorithms are reviewed, enhanced, and
compared that locate the corresponding reference frame for a given degraded
So far, many algorithms have been published that reliably predict the
visual quality of still images or temporally undistorted video sequences. In
this thesis, a new framework is presented that allows to evaluate the performance of these algorithms for temporally distorted video transmissions.
The processing steps and the signal representations follow the reasoning of
a human observer in a subjective experiment as observed in the first part
of the thesis. The improvements that can be achieved with the newly proposed framework are demonstrated by comparing the objective scores with
the subjective results of the comprehensive Multimedia Phase I database of
the Video Quality Experts Group.
Parity-based Error Detection with Recomputation for Fault-tolerant Spaceborne Computing
In radiation environment (e.g., space, nuclear reactor), electronics can fail due to bitflips in the flipflops of integrated circuits. A common solution is to triplicate the flipflops and connect their outputs to a voter. If one of the three bits is flipped, then the voter outputs the majority value and tolerates the error. This method is called triple modular redundancya (TMR). TMR can cause about 300% area redundancy. An alternative way is error detection with on-demand recomputation, where the recomputation is done by repeating the failed processing request to the processing circuit. The computation is done in consecutive transactions, which we call transaction-based processing. We implemented and evaluated the aforementioned alternative approach using parity checking on the Microsemi ProASIC3 FPGA, which is often used in space applications. The results show that parity-based error detection with our system recovery approach can save up to 54% of the area overhead that would be caused by the TMR, and achieve in most circuits slightly better timing results than TMR on ProASIC3. This area saving can be the key for fitting the application to a space-constrained chip.