整整一年后，我注意到我从未提供过答案。
在我想检索 3 个缩略图的原始问题中，我最终检索了 5 个。我还提到我不确定 FFmpeg 是否是一个合适的选项，这正是我使用的。
因此，在 中OnCreate，我确保支持 FFmpeg，然后执行以下操作：
if (FFmpeg.getInstance(getApplication()).isSupported()) {
@SuppressLint("SimpleDateFormat")
//ffmpeg expects the time format to be "00:00:00"
Format formatter = new SimpleDateFormat("00:" + "mm:ss.SS");
//Get the duration of the video
long duration = player.getDuration();
//Since I want 5 thumbnails, I divide the duration by 6 to get the first thumbnail position
long img1 = duration / 6;
//I format the first thumbnail time since ffmpeg expects "00:00:00" format
String firstTumbTime = formatter.format(img1);
//Scale the size of the thumbnail output (this can be improved/changed to your liking)
String scaledSize = displayMetrics.widthPixels / 7 + ":" + displayMetrics.heightPixels / 7;
//Set ffmpeg command (notice that I set vframes to one, since I only want 1 thumbnail/image)
String[] a = {"-ss", firstTumbTime, "-i", mStringFilePath, "-vframes", "1", "-s", scaledSize, imageThumbsDirectory + "/" + "thumb1.bmp"};
//start ffmpeg asynctask for the first thumbnail
ExecuteThumbFFMPEG(a);
} else {
Toast.makeText(TestNewPlayer.this, "Your device doesn't support FFMPEG...", Toast.LENGTH_SHORT).show();
}
上面代码中的注释说明了一切，现在这是我的ExecuteThumbFFMPEG方法。
public void ExecuteThumbFFMPEG(String[] command) {
ffmpegImages = FFmpeg.getInstance(this).execute(command, new ExecuteBinaryResponseHandler() {
@Override
public void onStart() {
//ffmpeg started
}
@Override
public void onProgress(String message) {
//get ffmpeg progress
}
@Override
public void onFailure(String message) {
//ffmpeg failed
}
@Override
public void onSuccess(String message) {
//first thumbnail saved successfully, now to get the other 4
//Scale the thumbnail output (Same as above)
String scaledSize = displayMetrics.widthPixels / 7 + ":" + displayMetrics.heightPixels / 7;
try {
//I first set the path/name for each thumbnail, this will also be used to check if the thumbnail is available or if we should get it
String imgPath1 = imageThumbsDirectory + "/" + "thumb1.bmp";
String imgPath2 = imageThumbsDirectory + "/" + "thumb2.bmp";
String imgPath3 = imageThumbsDirectory + "/" + "thumb3.bmp";
String imgPath4 = imageThumbsDirectory + "/" + "thumb4.bmp";
String imgPath5 = imageThumbsDirectory + "/" + "thumb5.bmp";
//Set the format again (same as above)
@SuppressLint("SimpleDateFormat")
Format formatter = new SimpleDateFormat("00:" + "mm:ss.SS");
//Get the length of the video
long duration = Player.getDuration();
//Divide the length of the video by 6 (same as above)
long time = duration / 6;
//Since I want 5 thumbnails evenly distributed throughout the video
//I use the video length divided by 6 to accomplish that
long img2 = time + time;
long img3 = time + time + time;
long img4 = time + time + time + time;
long img5 = time + time + time + time + time;
//Format the time (calculated above) for each thumbnail I want to retrieve
String Img2Timeformat = formatter.format(img2);
String Img3Timeformat = formatter.format(img3);
String Img4Timeformat = formatter.format(img4);
String Img5Timeformat = formatter.format(img5);
//Get reference to the thumbnails (to see if they have been created before)
File fileimgPath1 = new File(imgPath1);
File fileimgPath2 = new File(imgPath2);
File fileimgPath3 = new File(imgPath3);
File fileimgPath4 = new File(imgPath4);
File fileimgPath5 = new File(imgPath5);
//If thumbnail 1 exist and thumbnail 2 doesn't then we need to get thumbnail 2
if (fileimgPath1.exists() && !fileimgPath2.exists()) {
//Get/decode bitmap from the first thumbnail path to be able to set it to our ImageView that should hold the first thumbnail
Bitmap bmp1 = BitmapFactory.decodeFile(imgPath1);
//Set the first thumbnail to our first ImageView
imgone.setImageBitmap(bmp1);
//Set the ffmpeg command to retrieve the second thumbnail
String[] ffmpegCommandForThumb2 = {"-ss", Img2Timeformat, "-i", mStringFilePath, "-vframes", "1", "-s", scaledSize, imageThumbsDirectory + "/" + "thumb2.bmp"};
//Start ffmpeg again, this time we will be getting thumbnail 2
ExecuteThumbFFMPEG(ffmpegCommandForThumb2);
}
//If thumbnail 2 exist and thumbnail 3 doesn't then we need to get thumbnail 3
if (fileimgPath2.exists() && !fileimgPath3.exists()) {
//Get/decode bitmap from the second thumbnail path to be able to set it to our ImageView that should hold the second thumbnail
Bitmap bmp2 = BitmapFactory.decodeFile(imgPath2);
//Set the second thumbnail to our second ImageView
imgTwo.setImageBitmap(bmp2);
//Set the ffmpeg command to retrieve the third thumbnail
String[] ffmpegCommandForThumb3 = {"-ss", Img3Timeformat, "-i", mStringFilePath, "-vframes", "1", "-s", scaledSize, imageThumbsDirectory + "/" + "thumb3.bmp"};
//Start ffmpeg again, this time we will be getting thumbnail 3
ExecuteThumbFFMPEG(ffmpegCommandForThumb3);
}
////If thumbnail 3 exist and thumbnail 4 doesn't then we need to get thumbnail 4
if (fileimgPath3.exists() && !fileimgPath4.exists()) {
//Get/decode bitmap from the third thumbnail path to be able to set it to our ImageView that should hold the third thumbnail
Bitmap bmp3 = BitmapFactory.decodeFile(imgPath3);
//Set the third thumbnail to our third ImageView
imgThree.setImageBitmap(bmp3);
//Set the ffmpeg command to retrieve the fourth thumbnail
String[] ffmpegCommandForThumb4 = {"-ss", Img4Timeformat, "-i", mStringFilePath, "-vframes", "1", "-s", scaledSize, imageThumbsDirectory + "/" + "thumb4.bmp"};
//Start ffmpeg again, this time we will be getting thumbnail 4
ExecuteThumbFFMPEG(ffmpegCommandForThumb4);
}
////If thumbnail 4 exist and thumbnail 5 doesn't then we need to get thumbnail 5
if (fileimgPath4.exists() && !fileimgPath5.exists()) {
//Get/decode bitmap from the first fourth path to be able to set it to our ImageView that should hold the fourth thumbnail
Bitmap bmp4 = BitmapFactory.decodeFile(imgPath4);
//Set the fourth thumbnail to our fourth ImageView
imgFour.setImageBitmap(bmp4);
//Set the ffmpeg command to retrieve the last thumbnail
String[] ffmpegCommandForThumb5 = {"-ss", Img5Timeformat, "-i", mStringFilePath, "-vframes", "1", "-s", scaledSize, imageThumbsDirectory + "/" + "thumb5.bmp"};
//Start ffmpeg again, this time we will be getting thumbnail 5
ExecuteThumbFFMPEG(ffmpegCommandForThumb5);
}
//If thumbnail 5 exist, then we are done and we need to set it to our ImageView
if (fileimgPath5.exists()) {
Bitmap bmp5 = BitmapFactory.decodeFile(imgPath5);
imgFive.setImageBitmap(bmp5);
}
} catch (Exception ex) {
Toast.makeText(Player.this, String.valueOf(ex), Toast.LENGTH_SHORT).show();
}
}
@Override
public void onFinish() {
//ffmpeg is done
}
});
}
当用户退出Activity或被OnDestroy调用时，所有缩略图都应该被删除，我通过调用以下方法来做到这一点：
DeleteThumbs.deleteAllThumbnails(getBaseContext());
这是DeleteThumbs删除所有缩略图/图像的类
class DeleteThumbs {
@SuppressWarnings("unused")
static void deleteAllThumbnails(Context baseContext){
//Directory where all the thumbnails are stored
File imageThumbsDirectory = baseContext.getExternalFilesDir("ThumbTemp");
//Path to each thumbnail
File f1 = new File(imageThumbsDirectory + "/" + "thumb1.bmp");
File f2 = new File(imageThumbsDirectory + "/" + "thumb2.bmp");
File f3 = new File(imageThumbsDirectory + "/" + "thumb3.bmp");
File f4 = new File(imageThumbsDirectory + "/" + "thumb4.bmp");
File f5 = new File(imageThumbsDirectory + "/" + "thumb5.bmp");
boolean d1 = f1.delete();
boolean d2 = f2.delete();
boolean d3 = f3.delete();
boolean d4 = f4.delete();
boolean d5 = f5.delete();
}
}
由于我们知道每个缩略图的名称，因此很容易一次将它们全部删除。
这为我提供了 5 个缩略图图像，这些缩略图图像经过缩放以减少加载到ImageView's 中的时间。因为我将视频的持续时间除以 6，所以我得到了 5 张均匀“分布”在整个视频中的图像。
笔记：
这可以通过将图像缓存到内存中或使用像 picasso 或 glide 之类的库来为我们处理图像加载来改进。