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Why do video capture cards drop frames?

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Author : PURPLELEC
Update time : 2023-09-14 09:47:38
  The reasons for frame loss of video capture cards can be divided into two categories. One is caused by unreasonable and unmatched configuration of computer software and hardware, and the other is caused by low quality of video source. These reasons account for the majority.
  1. Computer software and hardware configuration:
  CPU: Some soft-compression capture cards require the computing power of the CPU to complete video encoding and compression. If capturing a small size such as 352x288 does not drop frames, but capturing a resolution of 720x576 does lose frames, the CPU may not be fast enough. quick. If you use VirtualDub software to collect, you can observe the CPU usage. If it reaches 100%, it is easy to lose frames. Generally speaking, the current mainstream CPUs are very fast and can more than handle ordinary collection, so most of the causes of frame loss are not caused by the CPU.
  Hard disk: Almost all current hard disks are DMA/33 or above. Even if they are 5400 rpm, they have a continuous writing speed of no less than 6MB/S. Therefore, the hard disk itself can meet most collection tasks. If you are running the Windows 98 operating system, you need to turn on the DMA of the hard disk, otherwise the reading and writing of the hard disk will occupy a lot of CPU usage or even 100%, so that the CPU does not have enough ability to encode the video information, resulting in frame loss. In addition, if possible, use a separate hard disk exclusively for collection, which can better ensure stable reading and writing of files.
  Software settings: Excluding video source factors, many reasons for frame loss are basically caused by improper software settings. Usually, Windows reads and writes to the hard disk through memory, so that when writing fragmented data, it can be broken into whole pieces, reducing the number of reads and writes to the hard disk and improving the overall operating efficiency. However, the amount of data collected by the video is large and continuous, so the Windows memory buffer must be canceled. Otherwise, when the data in the memory buffer is full, a large amount of data will not have time to be written to the hard disk, causing frame loss.
  If you use VirtualDub to collect, first switch to the Capture state, click the menu Capture->Disk I/O, confirm the Disable Windows write buffering setting and put a "√" in front of it, so that VirtualDub replaces the Windows buffering. When collecting, set the normal hard disk instructions. The light flashes continuously.
  If the frame loss is caused by poor compatibility of the whole machine, it will be more troublesome. Try installing various chip drivers that come with the computer motherboard, or even go to the motherboard manufacturer's homepage to download the latest BIOS and refresh the motherboard. If it doesn't work, you may need to change your computer.
video capture cards
  2. Video source:
  Excluding reasons related to computer configuration speed, the vast majority of frame drops are caused by the signal source. Under amateur conditions, common video sources include VHS/SVHS, Hi8/D8 and DV. Home VHS/SVHS is most likely to cause frame loss due to its own limitations.
  Tape mildew: VHS tapes are prone to mildew after being stored for a long time. During playback, the mold powder falls off and blocks the magnetic heads, causing video signal interruption and serious frame loss. The phenomenon on TV is generally that the image becomes unclear, the snowflakes are serious, the image is distorted, and finally there is a snowflake and no image.
  Solution: Find a way to clean the mold and frost off the video tape, and clean the video tape head frequently.
  Dust pollution: environmental dust pollution and trace amounts of magnetic powder falling off, sandwiched between the gap between the magnetic head and the tape, the video signal is occasionally lost, mainly due to the loss of the synchronization signal of line and field scanning, resulting in frame loss, and the image occasionally has bright spots and Lines and other interference. This kind of frame loss is usually accidental and relatively minor.
  Solution: Try to use new high-quality video tapes, keep them clean, especially outdoors and on open-air vehicles to prevent dust from invading the inside of the camera.
  High tape running resistance: The video tape is tight, causing the tape recorder's capstan tape to have high resistance, making the speed slow and unstable, and thus the frequency of the synchronization signal is also unstable. Viewed on a TV, the image tumbles or is distorted horizontally. The resulting frame loss is sometimes severe.
  Solution: Before shooting, make sure that the video tape can be rewinded easily. You can use the video recorder to smoothly rewind and rewind the video tape. You can also do this before playing.
  Track error: The track error between the external video tape and the local one is too large, and adjusting the track cannot solve the problem. As a result, the movement trajectory of the magnetic head never coincides with the video tape track. During playback, the TV screen appears to roll or distort at intervals. The resulting frame loss is sometimes so serious that it cannot even be collected.
  Solution: You can use the camera that shot this video tape to play it. If you can't get the original video tape, you can slightly adjust the tape transport mechanism of the video tape by yourself (if you are not sure, ask someone knowledgeable to do it). Open the casing of the video recorder and find the two adjustable guide posts at the front and rear of the drum of the video player. Use a special screwdriver with a notch in the middle (you can break off one end of the hacksaw blade from the fixing hole instead) and slightly adjust one of them. Guide the screws above and remember the angle of the screws before adjusting. This will slightly change the angle of the tape package on the drum until the TV picture is stable. Remember to restore it to its original state after use.
  The problem of frame loss in video capture cards is complex. We need to analyze the reasons, find out the main contradictions, and prescribe the right medicine to minimize frame loss as much as possible.