fread from asset

[yaggy]

I wonder if it's possible to fread(and f-thing stdio functions) files
in assets folder of apk.
The code below always lose response.

#include <android/asset_manager.h>
#include <android/asset_manager_jni.h>
void myLoadAsset(AAssetManager* mngr){
....
const char imageFilename[] = "image.png";
AAsset* asset = AAssetManager_open(mngr, imageFilename,
AASSET_MODE_UNKNOWN);
FILE* fp = (FILE*)AAsset_getBuffer(asset);
size_t imageSize = AAsset_getRemainingLength(asset);
unsigned char *pImage = (unsigned char*)malloc(sizeof(unsigned
char) * imageSize);
AAsset_seek(asset, 0, SEEK_SET); // or fseek(fp, 0, SEEK_SET);
fread(pImage, 1, imageSize, fp);
....
}

I changed AAsset_seek to fseek but the result was the same.
I've already checked pImage, imageSize and fp have valid values.

[Krystian Bigaj]

AAsset_getBuffer gives you direct pointer to your data in memory, not
a FILE*.

You could use only AAsset_openFileDescriptor() (with seek,read), but
your assets must be not compressed (which for now I see depends on
file extension, google for kNoCompressExt).
Also when using AAsset_openFileDescriptor keep in mind that it gives
you handle/fd to opened .apk file, so seek() is not relative to opened
file, but to .apk file.

Personally I would stick to AAsset_getBuffer+AAsset_getLength (you get
pointer to your whole file data in memory, or as a mmap), or
AAsset_read+AAsset_seek+AAsset_getLength+...

[yaggy]

Thank you for your commnet, Krystian.
Now I understand asset manager is not a bridge to FILE, but totally
another way to handle assets.

My purpose is to load PNG format data with libpng. I'll try it with
mapped image on memory.

yaggy

[Ignacio Vela]

I need to open a file (avi) in ndk.

I can't figure how can I have access to this file that should be in my application files. Can please somebody give an example?

I've read that if I change the extension to mpg the file won't be compressed, but in this case how can I get the file path to open it in C?

Thanks!

[Zoran Angelov]

Hi,

i hope this can help you : http://groups.google.com/group/android-ndk/browse_thread/thread/a69084018e87a5a8/bf9a47737378fe06

And after you get native file descriptor you can change read function of libpng's png_structp with calling png_set_read_fn .

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[Zoran Angelov]

If you place the file in res/raw it won't be compressed.

For reading it with native C file-descriptor functions read the the message-thread link posted previously.

I'm using that method for opening multimedia files with ffmpeg and it works great.

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[Crossle Song]

I use this code, but can not open file in FFmpeg, can you tell me How to open asset video mp4 file in FFmpeg
 
   AAssetManager *mgr = AAssetManager_fromJava(env, assetManager);
    const char *fname = (*env)->GetStringUTFChars(env, name, NULL);
    AAsset *asset = AAssetManager_open(mgr, fname, AASSET_MODE_STREAMING);
  (*env)->ReleaseStringUTFChars(env, name, fname);
    off64_t start, length;
    int fd = AAsset_openFileDescriptor64(asset, &start, &length);
    AAsset_close(asset);

   char str[128];
   snprintf(str, 128, "pipe:%d", fd); // fd:

[emymrin]

@Crossle Song

You can do that by implementing and registering your own URLProtocol.

[Alex Cohn]

On Tuesday, December 17, 2013 11:32:39 AM UTC+2, Crossle Song wrote:

I use this code, but can not open file in FFmpeg, can you tell me How to open asset video mp4 file in FFmpeg
 
   AAssetManager *mgr = AAssetManager_fromJava(env, assetManager);
    const char *fname = (*env)->GetStringUTFChars(env, name, NULL);
    AAsset *asset = AAssetManager_open(mgr, fname, AASSET_MODE_STREAMING);
  (*env)->ReleaseStringUTFChars(env, name, fname);
    off64_t start, length;
    int fd = AAsset_openFileDescriptor64(asset, &start, &length);
    AAsset_close(asset);

   char str[128];
   snprintf(str, 128, "pipe:%d", fd); // fd:

See How to properly pass an asset FileDescriptor to FFmpeg using JNI in Android. TL;NR: ffmpeg pipe does not know about your start; luckily, you can initialize AVFormatContext with non-zero skip_initial_bytes and iformat.

BR,

Alex Cohn