Visual Circuits ReelTime 2, ReelTime 4, ReelTime Series User Manual

ReelTime Series Board Encoding Parameters

User Manual

Visual Circuits Corporation

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Visual Circuits 5155 East River Road, Suite 401 Minneapolis, MN 55421

http://www.visualcircuits.com

Visual Circuits Publication Number: 813-0015a

All specifications are subject to change without notice.

CONTENTS

Encoding Parameters . . . . . . . . . . . . . . . . . . . . . 1

Required Encoding Parameters. . . . . . . . . . . . . . . . . . .1

Encoding Recommendations. . . . . . . . . . . . . . . . . . . . .2

Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . 5

Stuttering files during Playback . . . . . . . . . . . . . . .5

"Latent Images" or "Flashing" during playback . . .6 SMPTE time codes are not recognized properly. . .7

On Screen (GIF) Overlay Information. . . . . . . . . . 9

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Contents

ENCODING PARAMETERS

Required Encoding Parameters

1. Files must be program stream MPEG2 files of audio/video, video only or audio only. Visual Circuits 4ReelTime Pro, 4ReelTime RGB and MPEG Plus products do not currently support transport stream MPEG files decoding.

2. Use 4:2:0, not 4:2:2 encoding.

3. In MPEG-2, both fields should be encoded. Thi s i s t he nor ma l default.

4. The audio track must be MPEG Layer 2. Files with audio and

video tracks cannot be mixed with video only or audio only files on the same channel during playback. It is recommended to encode a “blank” au dio track, if there is no audio is present on the original source tape. This will standardize all MPEG

files and provide easy future management of video content.

5. POPVideo Player – Standard (IDE Hard Drive): Recommended bit r ates for standa rd POPVideo Players a re 4-6 mbps per channel. The total bit rate of a POPVideo Player must not exceed 24 mbps across four channels (i.e. averaging 6 mbps per channel) . Channels may be encoded at different bit rates as long as 24 mbps is not exceeded across a single hard drive, 4-channel Player.

6. POPVideo Player – Upgrade (SCSI Hard Drive): POPvideo Players upgraded with SCSI hard drives will play up to 8 channels at 6 mbps per channel. The total bit rate of a SCSI POPvideo Play er must not exceed 4 8 mbps.

7. Recommended DVP Server (SCSI): Re commended bit rates for standard DVP servers are 6-10 mbps per channel. DVP Servers can support up to 15 mbps per channel and 40 mbps across one 4-channel Visual Circuits MPEG-2 decoder board. Larger, custom servers of 20-24 channels can sustain a maximum bit rate of 6 mbps per channel, regardless of hard disk drive configuration.

Encoding Parameters

Encoding Recommendations

1. Resolution: 720 X 480 or 704 X 480 in NTSC; 704 X 576 in PAL.

2. Closed GOP (Group of Pictures) with an “I-frame” every 15

frames is recommended.

3. The recommended audio bit rate is 384kbps and a sampling rate of 48khz. The audio output voltage of the 4ReelTime Pro/ Plus has a maximum level (without clipping) of 3.75v, or

11.5dBV (refere nce d t o 1v). The noise floor is -67db with files stopped. The noise floor changes to -44db when a file is playing. In our testing, we have found that some MPEG2 encoders ha ve s ome audio los s when encodin g. For e xample, a Vibrint encoder has a 3db audio loss. Some encoders may not have any loss. It is recommended to play back test files using the original source tapes to confirm audi o levels prior to encoding an entire project. This will allow for calibration of the encoding system to obtain the desired audio level.

4. The recommended bit rates are as follows: good quality or for scenes without much motion-- minimum 4 mega bits per second (mbps); for good quality with most content—6 mbps; for good quality with high-motion scenes—8 mbps; for demanding content—10 mbps; and for the highest possible quality with demanding material—15 mbps.

5. When encoding files annotate and store notes on the audio lev els of bot h the sourc e tape a nd input set tings of t he encoder. It then will be possible to verify audio levels of subsequently encoded files. It's desirable to maintain a baseline audio level across all files of a presentation whether at a sing le or multip le locations. If no encoding notes or data is available from previously encoded files, compar e the files. When possible measure audio levels of the source tapes and of the encoded

Encoding Parameters

files. At a minimum, listen to and compare fi les. Even if encoding is done at the same production facility, variances between sessions may occur. Once the MPEGs are encoded, the manipulation of the audio for each individual file is highly impractical.

6. MPEG files are const ructed from int ertwined (i .e. multiple xed) audio and vide o streams. The length of video a nd audio s tream segments within MPEG files should be identical if possible. Ending the audio segment at a .5 second interval (i.e., at an “I- frame”) will ensure identical stream lengt hs, pro vidi ng smooth and seamless looping playback.

7. When encoding SMPTE tracks it is recommended to encode these tracks "hot"--at approximately +6db. This adjustment can compensat e for s ome SMPTE i nform atio n that may be los t during compressio n. Not all encoders will resp ond in the same way. Sample testing should be done with all SMPTE tracks.

8. Crosschannel synchronized playback of files requires the MPEG-2 embedded time codes of each file to start at the same position (in the Group of Pictures- --GOP headers). If possi ble, start all time codes at “0“ for st an dardiz ation and ease o f use i n future ap plications.

9. Standard color bars and audio test tones should be encoded along with the “production” files f or r efere nce a nd calib rati on. These encoded display test/tuning files should be separate files--not headers or footers of the presentation files.

10. To playback still images or computer-based graphics, we recommend software encoders such as DVMPEG (www.darvision.com) Please refer to the separate chapter that addresses still image encoding and playback. Note: Multiplexing a blank audio track on video only files is highly recommended.

Encoding Parameters

TROUBLESHOOTING

Stuttering files during Playback

Irregular playback on single and multiple channels can be caused by a number of conditions:

1. Uneven audio to video track lengths : Confirm the length of the audio track to the length of t he video track . The V isu al Circuits VCC4PRO driver, st andard with all Visual Circ uit s boa rds and digital servers, aggressively synchronizes the audio and video data of the MPEG file to maintain Audio/Visual (AV) Sync. If the MPEG file’s audio and video tracks are uneven in length, the driver’s attempt to synchronize these uneven tracks will result in poor performance. Mismatched AV track lengths will

result in overall degradation of system performance. Often a "bad" file will cause uneven or stuttering playback on other channels of the syst em as well. Through digi tal edit ing, MPEG

2 fil es can be "demulti plex ed" (separ ating t he audio from vide o information). The audio and video tracks ca n t hen be edited to match. The two tr acks can then be "mult iplex ed" back toget her . Always test files individually if a file (or system) is suspected to have playback problems.

2. Mixed video only MPEG f iles with MPEG with video and audio data: Confirm that all files on a particular channel are either video only, audio only , or audio/ video f iles. I t is recommen ded to have a "blank" audio track encoded with all MPEG files-even if no audio is present on the source material. This will ensure compatibility, if MPEGs with audio/video information are introduced at a later date.

3. The bit rate of the MPEG files being played exceed the system capabilities: The Visual Circuit MPEG decoder boards and digital servers all have a maximum sustained bit rate that ca n be delivered. Refer to the system capabiliti es above for basic information. Always, consult your Visual Circuits representative prior to encoding or designing your installation if there are any questions.

Troubleshooting

4. Cross channel synchronization requires equal playback duration of MPEG files: For cross channel s ync all MPEG f il es

must have equal playback duration. If in a synchronized group of channels, files vary in length, the driver will attemp t to synchronize these unevenly matched files and cause "stuttering". Check file lengths and bit rates. It is recommended to encode files with equal bit rates whenever possible and files lengths that are exact.

"Latent Images" or "Flashing" during playback

1. Incorrect timecodes or improperly closed encoding session. If the incorrect timecode is given for a particular file it is possible to actually encode a frame or two of the trailer or header information from the source. Often this "extr a" frame is seen only briefly and may appear as a "flash" on the screen. Review the original source of the encoding and determine if the timecodes are correct or if the encoding session was actually closed on the proper frame.

2. Playing MPEG 1 and MPEG2 files back to back: The resolution switch from MPEG 1 files (342X240) to MPEG2 files (720X480) causes a "l atent image" or a "q uadrant displ ay" of the last played file ’s image. The only way to perform seamless playback when using a playlist of files is to insert an encoded "black file" with blank audio track, between MPEG 1 and MPEG 2 files. The black MPEG file preceding the playback fi le shoul d be of the same standa rd. In other wo rds , prior to an MPEG 1 file the "black file"--again with a blank audio track--should be MPEG 1 and vice versa. Changing the driver parameter "InitOnOpen" to "1" may also remedy this problem, as long as back to back "seamless" playback is not desired. Each file must be "loaded" individually prior to playing. (You can use th e Visual Circuits Dri v er editing utility "VccReg.exe" for changing this parameter.) However, testing should be done with this driver sett ing, as with all parameter

Troubleshooting

changes, to verify the overall effect on the presentation, especially in regards to cross channel synchronization. Incorporating a delay between files or calling the "mpgblack" command, which is actually a function call on the decoder card, will not solve the problem.

SMPTE time codes are not recognized properly

Some SMPTE tracks loose information during compression and may not "trigger" events as required. It is recommended to encode these tracks "hot"--adding approximately +6 db to the track while encoding. Again, testing is essential to account for variances in encoders and SMPTE devices involved. Note: Simple audio filters, used at the installation site, are also useful in eliminating "noise" and cleaning up the SMPTE signal.

Troubleshooting

ON SCREEN (GIF) OVERLAY INFORMATION

Graphic Interchange Format (GIF) files are created with standard graphics authoring programs. The following are basic creation guidelines and playback tips:

1. The width, or "X" axis, f the GIF’s resolution must be a multiple of 16 pixels.

2. GIF must be 16-color non-interlaced format. A palette of exactly 16 c olors (any colors) can be used.

3. Animated GIFS are not supported.

4. The GIF file should not go off the edge of the screen.

5. There must be an MPEG file underneath the GIF in order for the GIF to display properly. The MPEG does not have to be playing.

6. MPEG files using a GIF overlay, should be a minimum of 8 seconds in duration to ensure properly timed GIF display.

For further GIF creation tips and GIF display troubleshooting information refer to the "On Screen Display Guidelines" technical document.

NOTE

These guidelines serve only as recommendations and by no means represent technical data pertinent to any specific encoding device or process. It is recommended that prior to beginning any encoding project, sample files are played back on the systems to be used to ensure proper display quality.

Visual Circuits does provide encoding services. Visual Circuits cannot guarantee any third party encoding.