Testing sites agree that the 4K video from the Sony FDR X1000V has noticeably higher resolution than that from the GoPro Hero 4 Black, and that this is in part due to the higher bitrate (100Mbps versus 50 or 60 Mbps).

The Sony also has other advantages over the GoPro:

1. You can use it without the waterproof case, and it still has water resistance. The body has a standard tripod hole. The GoPro outside the waterproof case cannot be mounted on anything without an extra cost frame, and it is not weather resistant at all.

2. The Sony built-in mic is stereo, and the audio recording in XAVC S mode is uncompressed and higher (in specs) than CD quality. The fact that you can use the camera without the waterproof housing, even in the rain, also means that the audio will not be muffled.

3. Digital stabilization in HD mode.

4. Buit-in GPS (accurate time automatically).

5. Time code.

The attributes that are worse:

1. Lower dynamic range, although this has not been as systematically tested, with most reviewers using the default Sony ‘Vivid’ color setting, which ups saturation and contrast (crushed blacks). It may be that in “Natural’ mode the dynamic range is better.

2. Bluish tint (as opposed to the GoPro yellow tint).

I have also found that the Sony, like all darn Sony cameras, overexposes. That can contribute to blown highlights and video that looks like it has low dynamic range.

Indeed, the out-of-camera 4K video does not look very good, precisely because of overexposure and the blue. But both can be corrected, either in post or by using AE shift in the camera along with manual WB.

I shot a test video in 4K at 100Mbps using the Sony in its default modes. I was horrified by the video. But, by merely reducing luminance and correcting WB in post (using a white reference) I thought the resulting video looked very good. The video was shot while it was raining and used without the waterproof case (you can hear the drops and see in one clip a droplet on the lens). The audio quality can be assessed as well, with passing cars (l to r) and bird calls and songs.

Here is the test video I shot and edited (as described above - no grading, just correcting):

To give an idea of the difference between the ooc video and the end result, here are two frame grabs: one from the ooc video and the other corrected in post (from the uploaded video):

ooc:

http://i849.photobucket.com/albums/ab56/markr041/Sony%20Action%20Cam%202_zpsn7eo6xbo.jpg

Corrected:

http://i849.photobucket.com/albums/ab56/markr041/Sony%20Action%20Cam%202a_zpsyozelqlr.jpg