How to get device vender ID

To get the vendor ID of a USB device on Linux "lsusb" will tell you what's what:

steve@media:~/android-sdk-linux/tools$ lsusb
Bus 002 Device 003: ID 045e:0040 Microsoft Corp. Wheel Mouse Optical
Bus 002 Device 002: ID 046d:c315 Logitech, Inc. Classic New Touch Keyboard
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 011: ID 18d1:4e12
Bus 001 Device 006: ID 04b8:011f Seiko Epson Corp. Perfection 1670
Bus 001 Device 003: ID 1058:1003 Western Digital Technologies, Inc.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

How to say n^m

N的2次方: N Squared
N的3次方: N Cubed
N的M次方: N the M power

N开M次方: the M root of N

CheckJNI of NewStringUTF

In file Check dalvik/vm/checkjni.c

This is the function which check the input string of NewStringUTF is a valid UTF8 or not.
If not valid, the check function will abort the VM.
That caused our application got crashed when there are some mal-formated UTF8 string.

/*
* Verify that "bytes" points to valid "modified UTF-8" data.
*/
static void checkUtfString(JNIEnv* env, const char* bytes, bool nullOk,
    const char* func)
{
    const char* origBytes = bytes;
    if (bytes == NULL) {
        if (!nullOk) {
            LOGW("JNI WARNING: unexpectedly null UTF string\n");
            goto fail;
        }
        return;
    }
    while (*bytes != '\0') {
        u1 utf8 = *(bytes++);
        // Switch on the high four bits.
        switch (utf8 >> 4) {
            case 0x00:
            case 0x01:
            case 0x02:
            case 0x03:
            case 0x04:
            case 0x05:
            case 0x06:
            case 0x07: {
                // Bit pattern 0xxx. No need for any extra bytes.
                break;
            }
            case 0x08:
            case 0x09:
            case 0x0a:
            case 0x0b:
            case 0x0f: {
                /*
                 * Bit pattern 10xx or 1111, which are illegal start bytes.
                 * Note: 1111 is valid for normal UTF-8, but not the
                 * modified UTF-8 used here.
                 */
                LOGW("JNI WARNING: illegal start byte 0x%x\n", utf8);
                goto fail;
            }
            case 0x0e: {
                // Bit pattern 1110, so there are two additional bytes.
                utf8 = *(bytes++);
                if ((utf8 & 0xc0) != 0x80) {
                    LOGW("JNI WARNING: illegal continuation byte 0x%x\n", utf8);
                    goto fail;
                }
                // Fall through to take care of the final byte.
            }
            case 0x0c:
            case 0x0d: {
                // Bit pattern 110x, so there is one additional byte.
                utf8 = *(bytes++);
                if ((utf8 & 0xc0) != 0x80) {
                    LOGW("JNI WARNING: illegal continuation byte 0x%x\n", utf8);
                    goto fail;
                }
                break;
            }
        }
    }
    return;
fail:
    LOGW("             string: '%s'\n", origBytes);
    showLocation(dvmGetCurrentJNIMethod(), func);
    abortMaybe();
}

Android CheckJNI

CheckJNI can catch a number of common errors.

A simple way to enable or disable JNI:
adb remount
adb pull /system/build.prop .

delete or add line ro.kernel.android.checkjni=1

adb push build.prop /system/.
adb shell reboot


Reference:
http://android-developers.blogspot.com/2011/07/debugging-android-jni-with-checkjni.html

FFmpeg build and run

How to build and run ffmpeg 0.8

1. download 0.8 ffmepg

2. Install libsdl libsdl-mix, using synaptic package manager

3 ./configure --enable-gpl --enable-nonfree --enable-pthreads --enable-shared --disable-yasm --enable-debug=3 --disable-stripping --prefix=/home/xgu/ffmpeg

4. make; make install;

5. cd /home/xgu/ffmpeg/bin

6. LD_LIBRARY_PATH=../lib ./ffmpeg -s 640x480 -f video4linux2 -i /dev/video0 -f mpegts -vcodec mpeg2video out1.mpeg

7. LD_LIBRARY_PATH=../lib ./ffplay  Some_Video_File

Video Audio Capture in Linux

Video
Webcam support in Linux is mainly provided by the Linux UVC Project's UVC driver.

The UVC driver implements the Video4Linux 2 (V4L2) API

The specification of V4L2 API can be found at http://v4l2spec.bytesex.org/

Example:
In ffmpeg, file libavdevice/v4l2.c
http://v4l2spec.bytesex.org/v4l2spec/capture.c

Command:
#To capture video
ffmpeg -f video4linux2 -i /dev/video0 out.mpeg


Audio
Ubuntu is using ALSA for audio input output

Command:
#To capture audio
ffmpeg -f alsa -ac 2 -i hw:0 alsaout.wav

#To get hardware info
arecord -l



Reference:
http://ffmpeg.org/ffmpeg-doc.html
http://www.ideasonboard.org/uvc/
https://help.ubuntu.com/community/Webcam
https://help.ubuntu.com/community/UVC
http://v4l2spec.bytesex.org/
http://www.alsa-project.org/

Encode PCM to M4A

ffmpeg -i audiobo.aiff -strict experimental  -acodec aac  -ab 64k -ar 22050 a.m4a