Well, what I can say is what the admin already said elsewhere: the JXD 951 has great hardware, but the firmware stains the overall quality of the player...
The construction quality is solid. The buttons at first, seemed a bit loose but they're quite responsive. The reset button is located at the bottom of the player and can be pressed easily (and you will use it quite often, believe me). The player has 1 on/off button, Vol+ and Vol- buttons, Snapshot button (located at the top), play/pause button, forward and back buttons, Menu button, Esc button (located next to the screen) and the already mentioned reset button.
When you connect it to the pc, you see that it already has 5 folders: DCIM (which contains the 100MEDIA folder, where you put your photos and videos), EBOOK (txt files for reading), FLASH (swf files, flash videos), GAME (NES rom files) and MP3 (music).
The menu layout is good and the player is simple to use, although I guess some options are not in the manual (like the fast forward / rewind option, that I happened to discover by chance). The menu contains:
For video playback its quality is very, very good. It's smooth and you can play the videos on it's native resolution without need of converting (I only tried AVIs yet - also the avi needs to be at a constant bit rate. VBR avi's have a jerky playback. It will also play all your Rockchip converted movies, if you had one. This player has a bookmark feature. When you stop a movie, it will ask you if you want to store your current time, so you can pick up where you left the next time you open the video player. But this only works for one movie, so you can't have more than one bookmark. Also, as I said, to use the fast forward / rewind function you need to push the Snapshot button once first and then the forward / back buttons. You have 2x, 4x and 8x speeds but it's slow and the videos tend to get out of sync (at least AVIs do, asf don't seem to suffer from this problem).
Music playback is good. You cannot have your music in folders or else the player will not find them, you need to transfer them to the MP3 folder in the player. You also have 4 EQ modes: Classic, Pop, Bass, Rock. As far as I can tell this player can't read OGG as I thought it should, but I don't know if it was the codec I used. Probably it wont read OGG at all.
For viewing pictures. The screen quality once again is useful here.
For taking pictures. The resolution goes from 320x240 to 1600x1200 but above 1024x768 you start to get pictures with some artifacts. But if you don't go above that, the quality of the pictures is very good, in fact I was surprised. You can choose the quality (high, middle, low), 6 effects and change the contrast. The player also has an option to put a date label in your photos (but you can turn that off) and a 4x digital zoom.
Record videos with the camera. This was one of the aspects of the player I was most disapointed with. You can record at 720x480 but the compression used is not very good even in the best setting and the audio recording is bad. The 320x240 videos are a bit better in terms of FPS but the audio is the same.
Record Audio with Mic or Line-In. Another function badly developed. If you choose to record using the Mic, the quality is 32Kbps at 8KHz. Using the Line-In option (choose it with the volume buttons) is 64Kbps at 32KHz. I was expecting the player to be capable of recording at 128kbps but if it does I haven't found the option to change the bit rates. (If anybody knows, please tell me).
Plays 2 built in games and NES roms. Although the player has a NES emulator, the key layout makes it impossible to play games. I guess they implemented this feature just because the chip is capable of it.
Contains an English-Chinese dictionary and the E-Book function. In some words of the dictionary, you can see a speaker, so I guess you can hear the word but until now I didn't find out how. Maybe the speaker doesn't mean nothing.
Contains a Calendar, Calculator, Notepad (the same as E-Book), a memory option (where you can change between the flash memory and the SD card and format the flash memory) and the upgrade feature. I read elsewhere that you shouldn't use the player to format SD cards because they become unusable. Don't know if it's true but I never tried this.
Where you can configure the player. Language, TV-Out, Default (reset to default options), Sound, Auto-Off, Style (2 skins), Time and Volume.
Where you can view Flash files. I haven't used this much but the swf file I tested worked although the image quality was not so good and not fullscreen.
Where you can use the AV In feature. You can record at two resolutions (320x240 and 640x480) and choose between 2 file formats: AVI and ASF. From what I noticed the ASF takes just a bit more disk space. The video quality is not very good but it's not bad either and the video is always at 30 fps. I guess if the firmware was a bit better the recordings would also be better. If you choose to record at 640x480 you can record 2h45 mins of video (if you don't have nothing stored in the memory) and at 320x240 you can record 4h and a half more or less. Now for the worst part: every time I tried to record at 640x480 and the recording time exceeded 1 hour, the player freezes the moment you press stop. You then have to reset the player and the file is lost, even though it still uses disk space. You have to format the player if you want to remove it. I don't know how much time you can record at 640x480 without the player freezing because I always recorded movies with 1h30 min, but I also recorded 10 min clips that worked just fine. When recording at 320x240 I was able to record 2h30 mins with no problem. I just pressed stop and everything was fine. I hope that JXD will release a new firmware to fix this :\
I'll try to add some pictures soon