subject: In the wireless network to transmit audio / video - wireless networking, audio, video - Communications Industry [print this page] In the wireless network to transmit audio / video - wireless networking, audio, video - Communications Industry
MPEG-1 with its subset called "constrained parameter bit stream", or the performance of the CPB is widely used. This performance is stored in the CD-ROM Red Book audio standard compliance requirements, the same number of video and audio data and design. This means that a 74 minutes of CD-ROM, you can save a full 74 minutes of video and audio. This standard is known as the White Paper or video CD (VCD). At 44.1kHz sampling rate conditions, the video data rate is set at 1.15Mb / s, audio data rate of 224Kb / s; video size is locked to 352x240 30fps NTSC and 352x280 25fpsPAL (also known as the CIF).
This standard is working well, but only the "standard" television performance of a quarter, and often caused controversy in the television public, but at that time was this is still an amazing technological achievements. About 1.5Mbit / s (125Kbytes / s) bit rate, the existing cable modem can easily transfer MPEG-1CPB flow, but for wireless cellular networks, to reliably do this there is still a long way to go. In addition, MPEG-1 network transmission and the lack of correct re-synchronization errors. MPEG-2 has this functionality, but to the actual implementation of the technology to catch up with the time, MPEG-4 and other streaming format has been displayed in front of people.
MPEG-2 has a higher data transfer rates, which range from 6 to 10Mbit / s. Bit rate 6Mbit / s and 9Mbit / s between the MPEG-2 (720x480 resolution) is ideal for DVD, it has also been selected to do the work; however, that under the bit rate, network traffic should more difficult, but the picture quality can be achieved watching television standards. MPEG-2 also has the packet, fault tolerance and correction, fast forward, rewind and other functions required for broadcasting. Then the MPEG-2 is also suitable for wireless / mobile streaming video equipment? Network channel must be 1MB / s data transfer rate to ensure reliable MPEG-2 video transmission, playback, and can be watched. Therefore, people have been exploring the best of the video stream format. MPEG-4 is the answer.
Why the answer is in the MPEG-4?
Requirements: high compression ratio, high video quality and powerful system layer; MPEG-4 wireless mobile video devices can provide satisfactory performance. (Note: This does not refer to MPEG-3, MPEG-2 directly from the rising to the MPEG-4; often mistaken for the MP3 is MPEG-3 audio is actually MPEG-1 Audio Layer III).
MPEG-4 format 1MBit / s bit rate can achieve the quality of MPEG-2720x480 resolution. If the video reduced to MPEG-1CPB, can be 350KBit / s data rate and reasonable can receive video. Further minimize the ratio may be 100KB / s data rate. Of course, due to the decline in the quality of video is not worth reading. We believe that the resolution of 352x240 or common interchange format (CIF, CommonInterchangeFormat) is the minimum acceptable video clarity. QCIF very interesting and in some network channel is essential. Table 1 lists the common terms of video resolution.
We would not consider the video resolution of the problem, first to see if suitable for wireless transmission using MPEG-4 video streams. To answer this question, we have two ways to study the MPEG-4?? Video compression capabilities and system layer. Existing mobile phone use general packet radio service (GPRS) standard 2.5G technology, the network data transfer rate can reach close to 112kbps. This rate is not fast, not too reliable, and see where you use. 3G network data transfer rate close to 2Mbps, which is a big improvement. Although 2.5Gw/GPRS can support a number of video streams, but until the advent of 3G, mobile phone anytime, anywhere using only universal up to watch the video stream. Of course, the wider the data pipeline, the higher video quality.
We now take a closer look at some data, in order to include them in the article. Most of the broadband network data rate is the number of bits used to represent every few seconds. Since each byte has 8 bits, so we put it more simply expressed as the number of bytes per second or bps divided by 8. So, 2.5Gw/GPRS is 14,000 bytes per second speed of the channel (14kBps. Note: capital B that byte). Accordingly, 3G is the rate 250kBps channel. 1X CD-ROM drive under the speed of transferring data 150kBps. As the 3G bandwidth for the 250kBps, in theory, will be MPEG-1CPB video, audio streams directly to the 3G receiver should be no problem. Of course, we may be only 60% of channels to the video service, but this effect can be a very good video. Since it's compression is much better than MPEG-1, then we can use 3G technology is the effect of what DVD format. On the MPEG-4, the answer was yes.
MPEG-1 data rate required per second 600kBps (4.8Mbps) channel, to achieve full D1 video resolution. This obviously requires less bandwidth 3G budget. DVD (currently using MPEG-2 video compression) constant speed of 6Mbps per second compression. Therefore, in order to experience the video content using the 3G technology, compression technology is not needed is not MPEG-1 MPEG-2. Now we still do not know the implementation of the first generation of 3G technology can make DVD video experience possible; but if possible, that MPEG-4 compression technology and the related can give us a direction. Then the current 3G technology enables the ultimate video performance to what kind of state do, we think that will be CIF. As mentioned above, 30 frames of the CIF image quality is quite clear, was designated as the current video benchmark. So, if the channel transmission rate of 2Mbps, which CPBVCD they adapt to this channel, why not directly use the MPEG-1 do? The reason is simple, in the same bit rate, MPEG-4 compression efficiency is that it's 3 times, and under certain conditions will be more efficient. This means that the transmission rate of 300-400kbps to 1.2Mbps MPEG-4 stream and under the MPEG-1 CPB CI has the same picture quality.
Fujitsu MPEG-4 chip has been added to the mobile media processor (MMP) of the new product line. Fujitsu energy-efficient MPEG-4 core to 2Mbps per second bit rate and speed per second for the CIF 30fps encoding or decoding (see Figure 5), compared to the standard frame rate to 15fps in QCIF for video calling. MPEG-4 core has two noteworthy features. First, the movement of vector technology with adaptive motion estimation computation circuit monitoring system of traditional sports 1 / 20. Second,
