Fix compatibility with old FFmpeg

V4L2 sink used a "url" field format AVFormatContext which has been
introduced in lavf 58.7.100.

Fixes #2382 <https://github.com/Genymobile/scrcpy/issues/2382>

Refs <https://github.com/FFmpeg/FFmpeg/commit/ea3672b7d67c432724bdbc8de0221f869b6a04c6>
Refs <https://github.com/FFmpeg/FFmpeg/commit/fa8308d3d4f27d6fb38ac2069887a7b259f1c6ab>

README.md

@@ -709,15 +709,15 @@ There is no visual feedback, a log is printed to the console.
 
 #### Push file to device
 
-To push a file to `/sdcard/Download/` on the device, drag & drop a (non-APK)
+To push a file to `/sdcard/` on the device, drag & drop a (non-APK) file to the
-file to the _scrcpy_ window.
+_scrcpy_ window.
 
 There is no visual feedback, a log is printed to the console.
 
 The target directory can be changed on start:
 
 ```bash
-scrcpy --push-target=/sdcard/Movies/
+scrcpy --push-target=/sdcard/Download/
 ```
 
 

app/scrcpy.1

@@ -133,7 +133,7 @@ but breaks the expected behavior of alpha keys in games (typically WASD).
 .BI "\-\-push\-target " path
 Set the target directory for pushing files to the device by drag & drop. It is passed as\-is to "adb push".
 
-Default is "/sdcard/Download/".
+Default is "/sdcard/".
 
 .TP
 .BI "\-r, \-\-record " file

app/src/cli.c

@@ -129,7 +129,7 @@ scrcpy_print_usage(const char *arg0) {
         "    --push-target path\n"
         "        Set the target directory for pushing files to the device by\n"
         "        drag & drop. It is passed as-is to \"adb push\".\n"
-        "        Default is \"/sdcard/Download/\".\n"
+        "        Default is \"/sdcard/\".\n"
         "\n"
         "    -r, --record file.mp4\n"
         "        Record screen to file.\n"

app/src/file_handler.c

@@ -6,7 +6,7 @@
 #include "adb.h"
 #include "util/log.h"
 
-#define DEFAULT_PUSH_TARGET "/sdcard/Download/"
+#define DEFAULT_PUSH_TARGET "/sdcard/"
 
 static void
 file_handler_request_destroy(struct file_handler_request *req) {

app/src/v4l2_sink.c

@@ -181,16 +181,16 @@ sc_v4l2_sink_open(struct sc_v4l2_sink *vs) {
     // <https://github.com/FFmpeg/FFmpeg/commit/0694d8702421e7aff1340038559c438b61bb30dd>
     vs->format_ctx->oformat = (AVOutputFormat *) format;
 #ifdef SCRCPY_LAVF_HAS_AVFORMATCONTEXT_URL
-    vs->format_ctx->url = strdup(vs->device_name);
+# define CTX_URL_FIELD url
+#else
+# define CTX_URL_FIELD filename
+#endif
+    vs->format_ctx->CTX_URL_FIELD = strdup(vs->device_name);
     if (!vs->format_ctx->url) {
         LOGE("Could not strdup v4l2 device name");
         goto error_avformat_free_context;
         return false;
     }
-#else
-    strncpy(vs->format_ctx->filename, vs->device_name,
-            sizeof(vs->format_ctx->filename));
-#endif
 
     AVStream *ostream = avformat_new_stream(vs->format_ctx, encoder);
     if (!ostream) {