remux: Fixed opening output file to support faststart option

remux.c

@@ -31,7 +31,10 @@ int main(int argc, char *argv[])
 	if (err = avformat_open_input(&demux, path, 0, 0))
 		job_failed("Opening input file failed: %s", av_err2str(err));
 	avformat_find_stream_info(demux, 0);
-	avformat_alloc_output_context2(&mux, 0, jstr(jlookup(argv[4], "format"), 0), path);
+	err = avformat_alloc_output_context2(&mux,
+			av_guess_format(jstr(jlookup(argv[4], "format"), 0), path, 0), 0, tmp);
+	if (err < 0)
+		job_failed("Error allocating muxer context: %s", av_err2str(err));
 	av_dict_copy(&mux->metadata, demux->metadata, 0);
 	parse_dict(&mux->metadata, jlookup(argv[4], "metadata"));
 	parse_chapters(mux, jlookup(argv[4], "chapters"), demux->duration);
@@ -74,6 +77,7 @@ int main(int argc, char *argv[])
 		if (err = av_interleaved_write_frame(mux, &pkt))
 			job_failed("Could not write frame: %s", av_err2str(err));
 	}
+	avformat_close_input(&demux);
 	av_interleaved_write_frame(mux, 0);
 	if (err = av_write_trailer(mux))
 		job_failed("Error writing trailer to temporary file", av_err2str(err));