How to convert .mkv to .flv with MKV to FLV Converter?
Upload MKV video to YouTube:
Many friends doubt about that MKV video shot off from Media Player Classic can not upload to YouTube, why? In fact, you have uploaded the incompatible format MKV video to YouTube, in this case, you can take MKV to FLV converter into consideration which is the main video format supported by YouTube.
MKV video to FLV converter:
MKV video to FLV converter can help you converter your favourite MKV video into FLV(YouTube), it also can transfer MKV files to WMV(Windows Movie maker)/AVI/MP4/MPG/MOV/VOB/3GP/RM etc which can be played on Blackberry/iPod/PSP/Apple TV/iPhone/Zune etc. Surely, Audio files with extensions like MP3/M4A/AC3/AAC/WMA /OGG are also can be extracted from MKV video and saved.
Further more, MKV video to FLV converter can preview original and edit the MKV video. You can cut unwanted parts of MKV video by specifing starting time and ending time through Trim, the blackedge can be removed through Crop. you can adjust brightness, contrast and saturation to make your MKV video looks more comfortable through Effect and set the resolution, frame rate, encoder and bitrate to make MKV video more suitable. In fact, you can merge your flies into one as you like and collect the attractive images in the video for collection on your PC by means of using the snapshot function.
MKV and FLV:
MKV(Matroska) is a universal format for storing common multimedia content, like movies or TV shows.
FLV is often used to display streaming media for its high rates of compression and a number of applications. FLV video is widely used on the video-sharing site, such as YouTube, Xinlang blog, Youku, Ku6, Tudou, Yahoo.

Tutorial 1: Convert MKV to FLV with MKV Converter
Step 1: Add your MKV file
You can add several MKV files one by one or load all MKV files from a whole folder at one time.

Step 2: Set the output format
Select the output format MPEG 4 in the profile drop-down list, and specify the output directory.

Step 3: Advanced settings
You can set the AVI video more accurately, including video resolution, frame rate, bit rate, and audio sample rate, channel, etc.

Step 4: Convert MKV to FLV
When all the necessary settings set OK, just press the "Start" button to begin converting your MKV file. 

Tutorial 2: Edit MKV video with MKV Converter
Click "Edit" icon, it pops up an editing dialog, which allows you to customize your personality video effects.
Tip 1: Crop MKV Movie
You can cut out the unwanted MKV video area, like black sides. Select "Full Screen" in Zoom list, tick "Custom Size" option, then you can customize video frame size according to the scale of cropped video.

Tip 2: Cut MKV video
Convert any clips of MKV video which you like most. You can set start/end time by clicking the up and down button in the Set start/end time box and click OK.

Tip 3: Adjust Video Effects
Customize your personality MKV video. Adjust video brightness, contrast, saturation, apply gray, emboss or old film effect, and set horizontal or vertical turning.

Tip 4: Take snapshots of MKV Video
You are allowed to take snapshots of the playing video while previewing by click camera icon under the preview window.

