Fastest way to load and display a jpeg on a SurfaceView?

Question

This is a bit of a followup to my last question: Canvas is drawing too slowly

Now that I can draw images more quickly, the problem I am faced with is that the actual loading of the images takes far too long.

In the app I am working on, the user is able to play back video frames (jpegs) in succession, as though he is viewing the video in realtime. I have been using BitmapFactory.decodeFile() to load each jpeg in a Bitmap. I'm unable to load all images at once since there are about 240 of them, and that would use up all of my heap space. What I have been doing is preloading up to 6 at a time into an array by way of a separate thread in order to cut down on the time it takes for each image to display.

Unfortunately, it takes somewhere between 50 and 90ms to load an image, and I need to show an image every 42ms. Is there a faster way to load images possibly?

For clarification, these images are in a folder on the SD card, and they are all 720x480 jpegs. I am sampling them at half that size to cut down on memory usage.

Answer 1

I ended up doing this quite a bit differently than I had originally envisioned. There was quite a bit to it, but here's the gist of how I achieved my goal:

1. All images are stored on SD card and written to one file (each image takes up X bytes in the file)
2. Use native code to read from and write to the image file
3. When requesting an image, I pass the index of the image in the list and a bitmap object (RGB_565) to the native code using a JNI wrapper
4. The native code locks the bitmap surface, writes pixel data (as a uint8_t**) directly to the bitmap, then unlocks it
5. The image is rendered to the screen

By doing it this way, I only needed to store one image in memory at a time, and I was able to bypass garbage collection (since the bitmap was only created once and then repopulated natively). I hope someone else might find this strategy useful.