fftools: Fix MediaCodec on Android15+

On Android15+ MediaCodec HAL backend was switched from HIDL to AIDL.
As a result, MediaCodec operations started to hang, see:

    https://trac.ffmpeg.org/ticket/11363
    https://github.com/termux/termux-packages/issues/21264
    https://issuetracker.google.com/issues/382831999

To fix that it is necessary to initialize binder thread pool.

Signed-off-by: Dmitrii Okunev <xaionaro@dx.center>

compat/android/binder.c

@@ -0,0 +1,114 @@
+/*
+ * Android Binder handler
+ *
+ * Copyright (c) 2025 Dmitrii Okunev
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+
+#if defined(__ANDROID__)
+
+#include <dlfcn.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "libavutil/log.h"
+#include "binder.h"
+
+#define THREAD_POOL_SIZE 1
+
+static void *dlopen_libbinder_ndk(void)
+{
+    /*
+     * libbinder_ndk.so often does not contain the functions we need, so making
+     * this dependency optional, thus using dlopen/dlsym instead of linking.
+     *
+     * See also: https://source.android.com/docs/core/architecture/aidl/aidl-backends
+     */
+
+    void *h = dlopen("libbinder_ndk.so", RTLD_NOW | RTLD_LOCAL);
+    if (h != NULL)
+        return h;
+
+    av_log(NULL, AV_LOG_WARNING,
+           "android/binder: unable to load libbinder_ndk.so: '%s'; skipping binder threadpool init (MediaCodec likely won't work)\n",
+           dlerror());
+    return NULL;
+}
+
+static void android_binder_threadpool_init(void)
+{
+    typedef int (*set_thread_pool_max_fn)(uint32_t);
+    typedef void (*start_thread_pool_fn)(void);
+
+    set_thread_pool_max_fn set_thread_pool_max = NULL;
+    start_thread_pool_fn start_thread_pool = NULL;
+
+    void *h = dlopen_libbinder_ndk();
+    if (h == NULL)
+        return;
+
+    unsigned thead_pool_size = THREAD_POOL_SIZE;
+
+    set_thread_pool_max =
+        (set_thread_pool_max_fn) dlsym(h,
+                                       "ABinderProcess_setThreadPoolMaxThreadCount");
+    start_thread_pool =
+        (start_thread_pool_fn) dlsym(h, "ABinderProcess_startThreadPool");
+
+    if (start_thread_pool == NULL) {
+        av_log(NULL, AV_LOG_WARNING,
+               "android/binder: ABinderProcess_startThreadPool not found; skipping threadpool init (MediaCodec likely won't work)\n");
+        return;
+    }
+
+    if (set_thread_pool_max != NULL) {
+        int ok = set_thread_pool_max(thead_pool_size);
+        av_log(NULL, AV_LOG_DEBUG,
+               "android/binder: ABinderProcess_setThreadPoolMaxThreadCount(%u) => %s\n",
+               thead_pool_size, ok ? "ok" : "fail");
+    } else {
+        av_log(NULL, AV_LOG_DEBUG,
+               "android/binder: ABinderProcess_setThreadPoolMaxThreadCount is unavailable; using the library default\n");
+    }
+
+    start_thread_pool();
+    av_log(NULL, AV_LOG_DEBUG,
+           "android/binder: ABinderProcess_startThreadPool() called\n");
+}
+
+void android_binder_threadpool_init_if_required(void)
+{
+#if __ANDROID_API__ >= 24
+    if (android_get_device_api_level() < 35) {
+        // the issue with the thread pool was introduced in Android 15 (API 35)
+        av_log(NULL, AV_LOG_DEBUG,
+               "android/binder: API<35, thus no need to initialize a thread pool\n");
+        return;
+    }
+    android_binder_threadpool_init();
+#else
+    // android_get_device_api_level was introduced in API 24, so we cannot use it
+    // to detect the API level in API<24. For simplicity we just assume
+    // libbinder_ndk.so on the system running this code would have API level < 35;
+    av_log(NULL, AV_LOG_DEBUG,
+           "android/binder: is built with API<24, assuming this is not Android 15+\n");
+#endif
+}
+
+#endif                          /* __ANDROID__ */

compat/android/binder.h

@@ -0,0 +1,31 @@
+/*
+ * Android Binder handler
+ *
+ * Copyright (c) 2025 Dmitrii Okunev
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef COMPAT_ANDROID_BINDER_H
+#define COMPAT_ANDROID_BINDER_H
+
+/**
+ * Initialize Android Binder thread pool.
+ */
+void android_binder_threadpool_init_if_required(void);
+
+#endif                          // COMPAT_ANDROID_BINDER_H

configure

@@ -7312,7 +7312,8 @@ enabled mbedtls           && { check_pkg_config mbedtls mbedtls mbedtls/x509_crt
                                check_pkg_config mbedtls mbedtls mbedtls/ssl.h mbedtls_ssl_init ||
                                check_lib mbedtls mbedtls/ssl.h mbedtls_ssl_init -lmbedtls -lmbedx509 -lmbedcrypto ||
                                die "ERROR: mbedTLS not found"; }
-enabled mediacodec        && { enabled jni || die "ERROR: mediacodec requires --enable-jni"; }
+enabled mediacodec        && { enabled jni || die "ERROR: mediacodec requires --enable-jni"; } &&
+                               add_compat android/binder.o
 enabled mmal              && { check_lib mmal interface/mmal/mmal.h mmal_port_connect -lmmal_core -lmmal_util -lmmal_vc_client -lbcm_host ||
                                { ! enabled cross_compile &&
                                  add_cflags -isystem/opt/vc/include/ -isystem/opt/vc/include/interface/vmcs_host/linux -isystem/opt/vc/include/interface/vcos/pthreads -fgnu89-inline &&

fftools/Makefile

@@ -51,6 +51,7 @@ OBJS-ffprobe +=                       \
     fftools/textformat/tw_buffer.o    \
     fftools/textformat/tw_stdout.o    \
 
+OBJS-ffmpeg += $(COMPAT_OBJS:%=compat/%)
 OBJS-ffplay += fftools/ffplay_renderer.o
 
 define DOFFTOOL

fftools/ffmpeg.c

@@ -78,6 +78,9 @@
 #include "libavdevice/avdevice.h"
 
 #include "cmdutils.h"
+#if CONFIG_MEDIACODEC
+#include "compat/android/binder.h"
+#endif
 #include "ffmpeg.h"
 #include "ffmpeg_sched.h"
 #include "ffmpeg_utils.h"
@@ -1019,6 +1022,10 @@ int main(int argc, char **argv)
         goto finish;
     }
 
+#if CONFIG_MEDIACODEC
+    android_binder_threadpool_init_if_required();
+#endif
+
     current_time = ti = get_benchmark_time_stamps();
     ret = transcode(sch);
     if (ret >= 0 && do_benchmark) {